| Message ID | 20210726163700.2092768-1-roberto.sassu@huawei.com |
|---|---|
| Headers | show |
| Series | integrity: Introduce DIGLIM | expand |
Em Mon, 26 Jul 2021 18:36:49 +0200 Roberto Sassu <roberto.sassu@huawei.com> escreveu: > Add an overview of DIGLIM to Documentation/security/diglim/introduction.rst > and the architecture to Documentation/security/diglim/architecture.rst > > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com> > --- > .../security/diglim/architecture.rst | 45 ++ > Documentation/security/diglim/index.rst | 11 + > .../security/diglim/introduction.rst | 631 ++++++++++++++++++ > Documentation/security/index.rst | 1 + > MAINTAINERS | 9 + > 5 files changed, 697 insertions(+) > create mode 100644 Documentation/security/diglim/architecture.rst > create mode 100644 Documentation/security/diglim/index.rst > create mode 100644 Documentation/security/diglim/introduction.rst > > diff --git a/Documentation/security/diglim/architecture.rst b/Documentation/security/diglim/architecture.rst > new file mode 100644 > index 000000000000..a54fe2453715 > --- /dev/null > +++ b/Documentation/security/diglim/architecture.rst > @@ -0,0 +1,45 @@ > +.. SPDX-License-Identifier: GPL-2.0 > + > +Architecture > +============ > + > +This section introduces the high level architecture of DIGLIM. > + > +:: > + > + 5. add/delete from hash table and add refs to digest list > + +---------------------------------------------+ > + | +-----+ +-------------+ +--+ > + | | key |-->| digest refs |-->...-->| | > + V +-----+ +-------------+ +--+ > + +-------------+ +-----+ +-------------+ > + | digest list | | key |-->| digest refs | > + | (compact) | +-----+ +-------------+ > + +-------------+ +-----+ +-------------+ > + ^ 4. copy to | key |-->| digest refs | > + | kernel memory +-----+ +-------------+ kernel space > + -------------------------------------------------------------------------- > + ^ ^ user space > + |<----------------+ 3b. upload | > + +-------------+ +------------+ | 6. query digest > + | digest list | | user space | 2b. convert > + | (compact) | | parser | > + +-------------+ +------------+ > + 1a. upload ^ 1b. read > + | > + +------------+ > + | RPM header | > + +------------+ > + > + > +As mentioned before, digest lists can be uploaded directly if they are in "before"? This is at the beginning of this document ;-) You should probably add a reference to introduction.rst here, like: As mentioned at Documentation/security/diglim/introduction.rst, ... > +the compact format (step 1a) or can be uploaded indirectly by the user > +space parser if they are in an alternative format (steps 1b-3b). > + > +During upload, the kernel makes a copy of the digest list to the kernel > +memory (step 4), and creates the necessary structures to index the digests > +(hash table and a linked list of digest list references to locate the > +digests in the digest list) (step 5). > + > +Finally, digests can be searched from user space through a securityfs file > +(step 6) or by the kernel itself. This probably applies to Documentation/security as a hole, but the best is to split the documents on two separate parts: - the kAPI and internals; - the admin-guide part. The audience for the admin-guide is distribution pagagers and syssadmins. > diff --git a/Documentation/security/diglim/index.rst b/Documentation/security/diglim/index.rst > new file mode 100644 > index 000000000000..0fc5ab019bc0 > --- /dev/null > +++ b/Documentation/security/diglim/index.rst > @@ -0,0 +1,11 @@ > +.. SPDX-License-Identifier: GPL-2.0 > + > +====================================== > +Digest Lists Integrity Module (DIGLIM) > +====================================== > + > +.. toctree:: > + :maxdepth: 1 > + > + introduction > + architecture > diff --git a/Documentation/security/diglim/introduction.rst b/Documentation/security/diglim/introduction.rst > new file mode 100644 > index 000000000000..d8d8b2a17222 > --- /dev/null > +++ b/Documentation/security/diglim/introduction.rst > @@ -0,0 +1,631 @@ > +.. SPDX-License-Identifier: GPL-2.0 > + > +Introduction > +============ > + > +Digest Lists Integrity Module (DIGLIM) is a new component added to the > +integrity subsystem in the kernel, primarily aiming to aid Integrity I would replace: "is a new component added to" -> "is a component of" As this is the kind of text that tends to be outdated with time... Imagine someone reading this paragraph maybe 10 years in the future ;-) > +Measurement Architecture (IMA) in the process of checking the integrity of > +file content and metadata. It accomplishes this task by storing reference > +values coming from software vendors and by reporting whether or not the > +digest of file content or metadata calculated by IMA (or EVM) is found > +among those values. In this way, IMA can decide, depending on the result of > +a query, if a measurement should be taken or access to the file should be > +granted. The `Security Assumptions`_ section explains more in detail why > +this component has been placed in the kernel. > + > +The main benefits of using IMA in conjunction with DIGLIM are the ability > +to implement advanced remote attestation schemes based on the usage of a > +TPM key for establishing a TLS secure channel [1][2], and to reduce the > +burden on Linux distribution vendors to extend secure boot at OS level to > +applications. > + > +DIGLIM does not have the complexity of feature-rich databases. In fact, its > +main functionality comes from the hash table primitives already in the > +kernel. It does not have an ad-hoc storage module, it just indexes data in > +a fixed format (digest lists, a set of concatenated digests preceded by a > +header), copied to kernel memory as they are. Lastly, it does not support > +database-oriented languages such as SQL, but only accepts a digest and its > +algorithm as a query. > + > +The only digest list format supported by DIGLIM is called ``compact``. > +However, Linux distribution vendors don't have to generate new digest lists > +in this format for the packages they release, as already available > +information, such as RPM headers and DEB package metadata, can be already > +used as a source for reference values (they already include file digests), -ETOMANY_already as "already" available... can be "already" ... "already" include... I would simplify the above text removing such redundancy. > +with a user space parser taking care of the conversion to the compact > +format. > + > +Although one might perceive that storing file or metadata digests for a > +Linux distribution would significantly increase the memory usage, this does > +not seem to be the case. As an anticipation of the evaluation done in the > +`Preliminary Performance Evaluation`_ section, protecting binaries and > +shared libraries of a minimal Fedora 33 installation requires 208K of > +memory for the digest lists plus 556K for indexing. > + > +In exchange for a slightly increased memory usage, DIGLIM improves the > +performance of the integrity subsystem. In the considered scenario, IMA > +measurement and appraisal with digest lists requires respectively less than > +one quarter and less than half the time, compared to the current solution. I found this paragraph a little bit confusing to understand. Could you please improve the description? I mean: what improved by one quarter? what improved by "less than half of the time"? > + > +DIGLIM also keeps track of whether digest lists have been processed in some > +way (e.g. measured or appraised by IMA). This is important for example for > +remote attestation, so that remote verifiers understand what has been > +uploaded to the kernel. > + > +DIGLIM behaves like a transactional database, i.e. it has the ability to > +roll back to the beginning of the transaction if an error occurred during > +the addition of a digest list (the deletion operation always succeeds). I don't think it makes sense to compare it with a transactional database. I would say, instead, something like: The inserts on DIGLIM are atomic: if an error occurs during the addition of a digest list, it rolls back the entire insert operation. > +This capability has been tested with an ad-hoc fault injection mechanism > +capable of simulating failures during the operations. > + > +Finally, DIGLIM exposes to user space, through securityfs, the digest lists > +currently loaded, the number of digests added, a query interface and an > +interface to set digest list labels. > + > +[1] LSS EU 2019 > + > +- slides: > + https://static.sched.com/hosted_files/lsseu2019/bd/secure_attested_communication_channels_lss_eu_2019.pdf > +- video: https://youtu.be/mffdQgkvDNY > + > +[2] FutureTPM EU project, final review meeting demo > + > +- slides: > + https://futuretpm.eu/images/07-3-FutureTPM-Final-Review-Slides-WP6-Device-Management-Use-Case-HWDU.pdf > +- video: https://vimeo.com/528251864/4c1d55abcd The above won't generate any cross-references with Sphinx. For it correct syntax, see: https://www.sphinx-doc.org/en/master/usage/restructuredtext/basics.html#citations > + > + > +Binary Integrity > +---------------- > + > +Integrity is a fundamental security property in information systems. > +Integrity could be described as the condition in which a generic > +component is just after it has been released by the entity that created it. Sounds a weird description for me. (ISC)2 defines integrity on its glossary[1] as: "Guarding against improper information modification or destruction and includes ensuring information non-repudiation and authenticity." [1] https://www.isc2.org/Certifications/CISSP/CISSP-Student-Glossary > +One way to check whether a component is in this condition (called binary > +integrity) is to calculate its digest and to compare it with a reference > +value (i.e. the digest calculated in controlled conditions, when the > +component is released). > + > +IMA, a software part of the integrity subsystem, can perform such > +evaluation and execute different actions: > + > +- store the digest in an integrity-protected measurement list, so that it > + can be sent to a remote verifier for analysis; > +- compare the calculated digest with a reference value (usually protected > + with a signature) and deny operations if the file is found corrupted; > +- store the digest in the system log. > + > + > +Contribution > +------------ I would rename this chapter to "Benefits". > + > +DIGLIM further enhances the capabilities offered by IMA-based solutions > +and, at the same time, makes them more practical to adopt by reusing > +existing sources as reference values for integrity decisions. > + > +Possible sources for digest lists are: > + > +- RPM headers; > +- Debian repository metadata. > + > + > +Benefits for IMA Measurement > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > + > +One of the issues that arises when files are measured by the OS is that, > +due to parallel execution, the order in which file accesses happen cannot > +be predicted. Since the TPM Platform Configuration Register (PCR) extend > +operation, executed after each file measurement, cryptographically binds > +the current measurement to the previous ones, the PCR value at the end of a > +workload cannot be predicted too. > + > +Thus, even if the usage of a TPM key, bound to a PCR value, should be > +allowed when only good files were accessed, the TPM could unexpectedly deny > +an operation on that key if files accesses did not happen as stated by the > +key policy (which allows only one of the possible sequences). > + > +DIGLIM solves this issue by making the PCR value stable over the time and > +not dependent on file accesses. The following figure depicts the current > +and the new approaches: > + > +:: > + > + IMA measurement list (current) > + > + entry# 1st boot 2nd boot 3rd boot > + +----+---------------+ +----+---------------+ +----+---------------+ > + 1: | 10 | file1 measur. | | 10 | file3 measur. | | 10 | file2 measur. | > + +----+---------------+ +----+---------------+ +----+---------------+ > + 2: | 10 | file2 measur. | | 10 | file2 measur. | | 10 | file3 measur. | > + +----+---------------+ +----+---------------+ +----+---------------+ > + 3: | 10 | file3 measur. | | 10 | file1 measur. | | 10 | file4 measur. | > + +----+---------------+ +----+---------------+ +----+---------------+ > + > + PCR: Extend != Extend != Extend > + file1, file2, file3 file3, file2, file1 file2, file3, file4 > + > + > + PCR Extend definition: > + > + PCR(new value) = Hash(Hash(meas. entry), PCR(previous value)) > + > +A new entry in the measurement list is created by IMA for each file access. > +Assuming that ``file1``, ``file2`` and ``file3`` are files provided by the > +software vendor, ``file4`` is an unknown file, the first two PCR values > +above represent a good system state, the third a bad system state. The PCR > +values are the result of the PCR extend operation performed for each > +measurement entry with the digest of the measurement entry as an input. > + > +:: > + > + IMA measurement list (with DIGLIM) > + > + dlist > + +--------------+ > + | header | > + +--------------+ > + | file1 digest | > + | file2 digest | > + | file3 digest | > + +--------------+ > + > +``dlist`` is a digest list containing the digest of ``file1``, ``file2`` > +and ``file3``. In the intended scenario, it is generated by a software > +vendor at the end of the building process, and retrieved by the > +administrator of the system where the digest list is loaded. > + > +:: > + > + entry# 1st boot 2nd boot 3rd boot > + +----+---------------+ +----+---------------+ +----+---------------+ > + 0: | 11 | dlist measur. | | 11 | dlist measur. | | 11 | dlist measur. | > + +----+---------------+ +----+---------------+ +----+---------------+ > + 1: < file1 measur. skip > < file3 measur. skip > < file2 measur. skip > > + > + 2: < file2 measur. skip > < file2 measur. skip > < file3 measur. skip > > + +----+---------------+ > + 3: < file3 measur. skip > < file1 measur. skip > | 11 | file4 measur. | > + +----+---------------+ > + > + PCR: Extend = Extend != Extend > + dlist dlist dlist, file4 > + > + > +The first entry in the measurement list contains the digest of the digest > +list uploaded to the kernel at kernel initialization time. > + > +When a file is accessed, IMA queries DIGLIM with the calculated file digest > +and, if it is found, IMA skips the measurement. > + > +Thus, the only information sent to remote verifiers are: the list of > +files that could possibly be accessed (from the digest list), but not if > +they were accessed and when; the measurement of unknown files. > + > +Despite providing less information, this solution has the advantage that > +the good system state (i.e. when only ``file1``, ``file2`` and ``file3`` > +are accessed) now can be represented with a deterministic PCR value (the > +PCR is extended only with the measurement of the digest list). Also, the > +bad system state can still be distinguished from the good state (the PCR is > +extended also with the measurement of ``file4``). > + > +If a TPM key is bound to the good PCR value, the TPM would allow the key to > +be used if ``file1``, ``file2`` or ``file3`` are accessed, regardless of > +the sequence in which they are accessed (the PCR value does not change), > +and would revoke the permission when the unknown ``file4`` is accessed (the > +PCR value changes). If a system is able to establish a TLS connection with > +a peer, this implicitly means that the system was in a good state (i.e. > +``file4`` was not accessed, otherwise the TPM would have denied the usage > +of the TPM key due to the key policy). > + > + > +Benefits for IMA Appraisal > +~~~~~~~~~~~~~~~~~~~~~~~~~~ > + > +Extending secure boot to applications means being able to verify the > +provenance of files accessed. IMA does it by verifying file signatures with > +a key that it trusts, which requires Linux distribution vendors to > +additionally include in the package header a signature for each file that > +must be verified (there is the dedicated ``RPMTAG_FILESIGNATURES`` section > +in the RPM header). > + > +The proposed approach would be instead to verify data provenance from > +already available metadata (file digests) in existing packages. IMA would > +verify the signature of package metadata and search file digests extracted > +from package metadata and added to the hash table in the kernel. > + > +For RPMs, file digests can be found in the ``RPMTAG_FILEDIGESTS`` section > +of ``RPMTAG_IMMUTABLE``, whose signature is in ``RPMTAG_RSAHEADER``. For > +DEBs, file digests (unsafe to use due to a weak digest algorithm) can be > +found in the ``md5sum`` file, which can be indirectly verified from > +``Release.gpg``. > + > +The following figure highlights the differences between the current and the > +proposed approach. > + > +:: > + > + IMA appraisal (current solution, with file signatures): > + > + appraise > + +-----------+ > + V | > + +-------------------------+-----+ +-------+-----+ | > + | RPM header | | ima rpm | file1 | sig | | > + | ... | | plugin +-------+-----+ +-----+ > + | file1 sig [to be added] | sig |--------> ... | IMA | > + | ... | | +-------+-----+ +-----+ > + | fileN sig [to be added] | | | fileN | sig | > + +-------------------------+-----+ +-------+-----+ > + > +In this case, file signatures must be added to the RPM header, so that the > +``ima`` rpm plugin can extract them together with the file content. The RPM > +header signature is not used. > + > +:: > + > + IMA appraisal (with DIGLIM): > + > + kernel hash table > + with RPM header content > + +---+ +--------------+ > + | |--->| file1 digest | > + +---+ +--------------+ > + ... > + +---+ appraise (file1) > + | | <--------------+ > + +----------------+-----+ +---+ | > + | RPM header | | ^ | > + | ... | | digest_list | | > + | file1 digest | sig | rpm plugin | +-------+ +-----+ > + | ... | |-------------+--->| file1 | | IMA | > + | fileN digest | | +-------+ +-----+ > + +----------------+-----+ | > + ^ | > + +------------------------------------+ > + appraise (RPM header) > + > +In this case, the RPM header is used as it is, and its signature is used > +for IMA appraisal. Then, the ``digest_list`` rpm plugin executes the user > +space parser to parse the RPM header and add the extracted digests to an > +hash table in the kernel. IMA appraisal of the files in the RPM package > +consists in searching their digest in the hash table. > + > +Other than reusing available information as digest list, another advantage > +is the lower computational overhead compared to the solution with file > +signatures (only one signature verification for many files and digest > +lookup, instead of per file signature verification, see `Preliminary > +Performance Evaluation`_ for more details). > + > + > +Lifecycle > +--------- > + > +The lifecycle of DIGLIM is represented in the following figure: > + > +:: You could just use: The lifecycle of DIGLIM is represented in the following figure:: > + > + Vendor premises (release process with modifications): > + > + +------------+ +-----------------------+ +------------------------+ > + | 1. build a | | 2. generate and sign | | 3. publish the package | > + | package |-->| a digest list from |-->| and digest list in | > + | | | packaged files | | a repository | > + +------------+ +-----------------------+ +------------------------+ > + | > + | > + User premises: | > + V > + +---------------------+ +------------------------+ +-----------------+ > + | 6. use digest lists | | 5. download the digest | | 4. download and | > + | for measurement |<--| list and upload to |<--| install the | > + | and/or appraisal | | the kernel | | package | > + +---------------------+ +------------------------+ +-----------------+ > + > +The figure above represents all the steps when a digest list is > +generated separately. However, as mentioned in `Contribution`_, in most > +cases existing packages can be already used as a source for digest lists, > +limiting the effort for software vendors. > + > +If, for example, RPMs are used as a source for digest lists, the figure > +above becomes: > + > +:: Same here. > + > + Vendor premises (release process without modifications): > + > + +------------+ +------------------------+ > + | 1. build a | | 2. publish the package | > + | package |-->| in a repository |---------------------+ > + | | | | | > + +------------+ +------------------------+ | > + | > + | > + User premises: | > + V > + +---------------------+ +------------------------+ +-----------------+ > + | 5. use digest lists | | 4. extract digest list | | 3. download and | > + | for measurement |<--| from the package |<--| install the | > + | and/or appraisal | | and upload to the | | package | > + | | | kernel | | | > + +---------------------+ +------------------------+ +-----------------+ > + > +Step 4 can be performed with the ``digest_list`` rpm plugin and the user > +space parser, without changes to rpm itself. > + > + > +Security Assumptions > +-------------------- > + > +As mentioned in the `Introduction`_, DIGLIM will be primarily used in > +conjunction with IMA to enforce a mandatory policy on all user space > +processes, including those owned by root. Even root, in a system with a > +locked-down kernel, cannot affect the enforcement of the mandatory policy > +or, if changes are permitted, it cannot do so without being detected. > + > +Given that the target of the enforcement are user space processes, DIGLIM > +cannot be placed in the target, as a Mandatory Access Control (MAC) design > +is required to have the components responsible to enforce the mandatory > +policy separated from the target. > + > +While locking-down a system and limiting actions with a mandatory policy is > +generally perceived by users as an obstacle, it has noteworthy benefits for > +the users themselves. > + > +First, it would timely block attempts by malicious software to steal or > +misuse user assets. Although users could query the package managers to > +detect them, detection would happen after the fact, or it wouldn't happen > +at all if the malicious software tampered with package managers. With a > +mandatory policy enforced by the kernel, users would still be able to > +decide which software they want to be executed except that, unlike package > +managers, the kernel is not affected by user space processes or root. > + > +Second, it might make systems more easily verifiable from outside, due to > +the limited actions the system allows. When users connect to a server, not > +only they would be able to verify the server identity, which is already > +possible with communication protocols like TLS, but also if the software > +running on that server can be trusted to handle their sensitive data. > + > + > +Adoption > +-------- > + > +A former version of DIGLIM is used in the following OSes: > + > +- openEuler 20.09 > + https://github.com/openeuler-mirror/kernel/tree/openEuler-20.09 > + > +- openEuler 21.03 > + https://github.com/openeuler-mirror/kernel/tree/openEuler-21.03 > + > +Originally, DIGLIM was part of IMA (known as IMA Digest Lists). In this > +version, it has been redesigned as a standalone module with an API that > +makes its functionality accessible by IMA and, eventually, other > +subsystems. > + > +User Space Support > +------------------ > + > +Digest lists can be generated and managed with ``digest-list-tools``: > + > +https://github.com/openeuler-mirror/digest-list-tools > + > +It includes two main applications: > + > +- ``gen_digest_lists``: generates digest lists from files in the > + filesystem or from the RPM database (more digest list sources can be > + supported); > +- ``manage_digest_lists``: converts and uploads digest lists to the > + kernel. > + > +Integration with rpm is done with the ``digest_list`` plugin: > + > +https://gitee.com/src-openeuler/rpm/blob/master/Add-digest-list-plugin.patch > + > +This plugin writes the RPM header and its signature to a file, so that the > +file is ready to be appraised by IMA, and calls the user space parser to > +convert and upload the digest list to the kernel. > + > + > +Simple Usage Example (Tested with Fedora 33) > +-------------------------------------------- > + > +1. Digest list generation (RPM headers and their signature are copied to > + the specified directory): > + > +.. code-block:: bash > + > + # mkdir /etc/digest_lists > + # gen_digest_lists -t file -f rpm+db -d /etc/digest_lists -o add > + > +2. Digest list upload with the user space parser: > + > +.. code-block:: bash > + > + # manage_digest_lists -p add-digest -d /etc/digest_lists > + > +3. First digest list query: > + > +.. code-block:: bash > + > + # echo sha256-$(sha256sum /bin/cat) > /sys/kernel/security/integrity/diglim/digest_query > + # cat /sys/kernel/security/integrity/diglim/digest_query > + sha256-[...]-0-file_list-rpm-coreutils-8.32-18.fc33.x86_64 (actions: 0): version: 1, algo: sha256, type: 2, modifiers: 1, count: 106, datalen: 3392 > + > +4. Second digest list query: > + > +.. code-block:: bash > + > + # echo sha256-$(sha256sum /bin/zip) > /sys/kernel/security/integrity/diglim/digest_query > + # cat /sys/kernel/security/integrity/diglim/digest_query > + sha256-[...]-0-file_list-rpm-zip-3.0-27.fc33.x86_64 (actions: 0): version: 1, algo: sha256, type: 2, modifiers: 1, count: 4, datalen: 128 > + > + > +Preliminary Performance Evaluation > +---------------------------------- > + > +This section provides an initial estimation of the overhead introduced by > +DIGLIM. The estimation has been performed on a Fedora 33 virtual machine > +with 1447 packages installed. The virtual machine has 16 vCPU (host CPU: > +AMD Ryzen Threadripper PRO 3955WX 16-Cores) and 2G of RAM (host memory: > +64G). The virtual machine also has a vTPM with libtpms and swtpm as > +backend. > + > +After writing the RPM headers to files, the size of the directory > +containing them is 36M. > + > +After converting the RPM headers to the compact digest list, the size of > +the data being uploaded to the kernel is 3.6M. > + > +The time to load the entire RPM database is 0.628s. > + > +After loading the digest lists to the kernel, the slab usage due to > +indexing is (obtained with slab_nomerge in the kernel command line): > + > +:: > + > + OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME > + 118144 118144 100% 0,03K 923 128 3692K digest_list_item_ref_cache > + 102400 102400 100% 0,03K 800 128 3200K digest_item_cache > + 2646 2646 100% 0,09K 63 42 252K digest_list_item_cache > + > +The stats, obtained from the ``digests_count`` interface, introduced later, > +are: > + > +:: > + > + Parser digests: 0 > + File digests: 99100 > + Metadata digests: 0 > + Digest list digests: 1423 > + > +On this installation, this would be the worst case in which all files are > +measured and/or appraised, which is currently not recommended without > +enforcing an integrity policy protecting mutable files. Infoflow LSM is a > +component to accomplish this task: > + > +https://patchwork.kernel.org/project/linux-integrity/cover/20190818235745.1417-1-roberto.sassu@huawei.com/ > + > +The first manageable goal of IMA with DIGLIM is to use an execution policy, > +with measurement and/or appraisal of files executed or mapped in memory as > +executable (in addition to kernel modules and firmware). In this > +case, the digest list contains the digest only for those files. The numbers > +above change as follows. > + > +After converting the RPM headers to the compact digest list, the size of > +the data being uploaded to the kernel is 208K. > + > +The time to load the digest of binaries and shared libraries is 0.062s. > + > +After loading the digest lists to the kernel, the slab usage due to > +indexing is: > + > +:: > + > + OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME > + 7168 7168 100% 0,03K 56 128 224K digest_list_item_ref_cache > + 7168 7168 100% 0,03K 56 128 224K digest_item_cache > + 1134 1134 100% 0,09K 27 42 108K digest_list_item_cache > + > + > +The stats, obtained from the ``digests_count`` interface, are: > + > +:: > + > + Parser digests: 0 > + File digests: 5986 > + Metadata digests: 0 > + Digest list digests: 1104 > + > + > +Comparison with IMA > +~~~~~~~~~~~~~~~~~~~ > + > +This section compares the performance between the current solution for IMA > +measurement and appraisal, and IMA with DIGLIM. > + > + > +Workload A (without DIGLIM): > + > +#. cat file[0-5985] > /dev/null > + > + > +Workload B (with DIGLIM): > + > +#. echo $PWD/0-file_list-compact-file[0-1103] > <securityfs>/integrity/diglim/digest_list_add > +#. cat file[0-5985] > /dev/null > + > + > +Workload A execution time without IMA policy: > + > +:: > + > + real 0m0,155s > + user 0m0,008s > + sys 0m0,066s > + > + > +Measurement > +........... > + > +IMA policy: > + > +:: > + > + measure fowner=2000 func=FILE_CHECK mask=MAY_READ use_diglim=allow pcr=11 ima_template=ima-sig > + > +``use_diglim`` is a policy keyword not yet supported by IMA. > + > + > +Workload A execution time with IMA and 5986 files with signature measured: > + > +:: > + > + real 0m8,273s > + user 0m0,008s > + sys 0m2,537s > + > + > +Workload B execution time with IMA, 1104 digest lists with signature > +measured and uploaded to the kernel, and 5986 files with signature accessed > +but not measured (due to the file digest being found in the hash table): > + > +:: > + > + real 0m1,837s > + user 0m0,036s > + sys 0m0,583s > + > + > +Appraisal > +......... > + > +IMA policy: > + > +:: > + > + appraise fowner=2000 func=FILE_CHECK mask=MAY_READ use_diglim=allow > + > +``use_diglim`` is a policy keyword not yet supported by IMA. > + > + > +Workload A execution time with IMA and 5986 files with file signature > +appraised: > + > +:: > + > + real 0m2,197s > + user 0m0,011s > + sys 0m2,022s > + > + > +Workload B execution time with IMA, 1104 digest lists with signature > +appraised and uploaded to the kernel, and with 5986 files with signature > +not verified (due to the file digest being found in the hash table): > + > +:: > + > + real 0m0,982s > + user 0m0,020s > + sys 0m0,865s > diff --git a/Documentation/security/index.rst b/Documentation/security/index.rst > index 16335de04e8c..6c3aea41c55b 100644 > --- a/Documentation/security/index.rst > +++ b/Documentation/security/index.rst > @@ -17,3 +17,4 @@ Security Documentation > tpm/index > digsig > landlock > + diglim/index > diff --git a/MAINTAINERS b/MAINTAINERS > index 6c8be735cc91..c914dadd7e65 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -5452,6 +5452,15 @@ L: linux-gpio@vger.kernel.org > S: Maintained > F: drivers/gpio/gpio-gpio-mm.c > > +DIGLIM > +M: Roberto Sassu <roberto.sassu@huawei.com> > +L: linux-integrity@vger.kernel.org > +S: Supported > +T: git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity.git > +F: Documentation/security/diglim/architecture.rst > +F: Documentation/security/diglim/index.rst > +F: Documentation/security/diglim/introduction.rst > + > DIOLAN U2C-12 I2C DRIVER > M: Guenter Roeck <linux@roeck-us.net> > L: linux-i2c@vger.kernel.org Thanks, Mauro
> From: Mauro Carvalho Chehab [mailto:mchehab+huawei@kernel.org] > Sent: Wednesday, July 28, 2021 1:10 PM > Em Mon, 26 Jul 2021 18:36:49 +0200 > Roberto Sassu <roberto.sassu@huawei.com> escreveu: > > > Add an overview of DIGLIM to > Documentation/security/diglim/introduction.rst > > and the architecture to Documentation/security/diglim/architecture.rst > > > > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com> > > --- > > .../security/diglim/architecture.rst | 45 ++ > > Documentation/security/diglim/index.rst | 11 + > > .../security/diglim/introduction.rst | 631 ++++++++++++++++++ > > Documentation/security/index.rst | 1 + > > MAINTAINERS | 9 + > > 5 files changed, 697 insertions(+) > > create mode 100644 Documentation/security/diglim/architecture.rst > > create mode 100644 Documentation/security/diglim/index.rst > > create mode 100644 Documentation/security/diglim/introduction.rst > > > > diff --git a/Documentation/security/diglim/architecture.rst > b/Documentation/security/diglim/architecture.rst > > new file mode 100644 > > index 000000000000..a54fe2453715 > > --- /dev/null > > +++ b/Documentation/security/diglim/architecture.rst > > @@ -0,0 +1,45 @@ > > +.. SPDX-License-Identifier: GPL-2.0 > > + > > +Architecture > > +============ > > + > > +This section introduces the high level architecture of DIGLIM. > > + > > +:: > > + > > + 5. add/delete from hash table and add refs to digest list > > + +---------------------------------------------+ > > + | +-----+ +-------------+ +--+ > > + | | key |-->| digest refs |-->...-->| | > > + V +-----+ +-------------+ +--+ > > + +-------------+ +-----+ +-------------+ > > + | digest list | | key |-->| digest refs | > > + | (compact) | +-----+ +-------------+ > > + +-------------+ +-----+ +-------------+ > > + ^ 4. copy to | key |-->| digest refs | > > + | kernel memory +-----+ +-------------+ kernel space > > + -------------------------------------------------------------------------- > > + ^ ^ user space > > + |<----------------+ 3b. upload | > > + +-------------+ +------------+ | 6. query digest > > + | digest list | | user space | 2b. convert > > + | (compact) | | parser | > > + +-------------+ +------------+ > > + 1a. upload ^ 1b. read > > + | > > + +------------+ > > + | RPM header | > > + +------------+ > > + > > + > > +As mentioned before, digest lists can be uploaded directly if they are in > > "before"? This is at the beginning of this document ;-) > > You should probably add a reference to introduction.rst here, like: > > As mentioned at Documentation/security/diglim/introduction.rst, ... Hi Mauro ok. > > +the compact format (step 1a) or can be uploaded indirectly by the user > > +space parser if they are in an alternative format (steps 1b-3b). > > + > > +During upload, the kernel makes a copy of the digest list to the kernel > > +memory (step 4), and creates the necessary structures to index the digests > > +(hash table and a linked list of digest list references to locate the > > +digests in the digest list) (step 5). > > + > > +Finally, digests can be searched from user space through a securityfs file > > +(step 6) or by the kernel itself. > > This probably applies to Documentation/security as a hole, but the > best is to split the documents on two separate parts: > - the kAPI and internals; > - the admin-guide part. > > The audience for the admin-guide is distribution pagagers and > syssadmins. Ok. I will create an admin-guide. > > diff --git a/Documentation/security/diglim/index.rst > b/Documentation/security/diglim/index.rst > > new file mode 100644 > > index 000000000000..0fc5ab019bc0 > > --- /dev/null > > +++ b/Documentation/security/diglim/index.rst > > @@ -0,0 +1,11 @@ > > +.. SPDX-License-Identifier: GPL-2.0 > > + > > +====================================== > > +Digest Lists Integrity Module (DIGLIM) > > +====================================== > > + > > +.. toctree:: > > + :maxdepth: 1 > > + > > + introduction > > + architecture > > diff --git a/Documentation/security/diglim/introduction.rst > b/Documentation/security/diglim/introduction.rst > > new file mode 100644 > > index 000000000000..d8d8b2a17222 > > --- /dev/null > > +++ b/Documentation/security/diglim/introduction.rst > > @@ -0,0 +1,631 @@ > > +.. SPDX-License-Identifier: GPL-2.0 > > + > > +Introduction > > +============ > > + > > +Digest Lists Integrity Module (DIGLIM) is a new component added to the > > +integrity subsystem in the kernel, primarily aiming to aid Integrity > > I would replace: > > "is a new component added to" -> "is a component of" > > As this is the kind of text that tends to be outdated with time... > Imagine someone reading this paragraph maybe 10 years in the future ;-) Ok. > > +Measurement Architecture (IMA) in the process of checking the integrity of > > +file content and metadata. It accomplishes this task by storing reference > > +values coming from software vendors and by reporting whether or not the > > +digest of file content or metadata calculated by IMA (or EVM) is found > > +among those values. In this way, IMA can decide, depending on the result > of > > +a query, if a measurement should be taken or access to the file should be > > +granted. The `Security Assumptions`_ section explains more in detail why > > +this component has been placed in the kernel. > > + > > +The main benefits of using IMA in conjunction with DIGLIM are the ability > > +to implement advanced remote attestation schemes based on the usage of > a > > +TPM key for establishing a TLS secure channel [1][2], and to reduce the > > +burden on Linux distribution vendors to extend secure boot at OS level to > > +applications. > > + > > +DIGLIM does not have the complexity of feature-rich databases. In fact, its > > +main functionality comes from the hash table primitives already in the > > +kernel. It does not have an ad-hoc storage module, it just indexes data in > > +a fixed format (digest lists, a set of concatenated digests preceded by a > > +header), copied to kernel memory as they are. Lastly, it does not support > > +database-oriented languages such as SQL, but only accepts a digest and its > > +algorithm as a query. > > + > > +The only digest list format supported by DIGLIM is called ``compact``. > > +However, Linux distribution vendors don't have to generate new digest lists > > +in this format for the packages they release, as already available > > +information, such as RPM headers and DEB package metadata, can be > already > > +used as a source for reference values (they already include file digests), > > -ETOMANY_already > > as "already" available... can be "already" ... "already" include... > > I would simplify the above text removing such redundancy. Ok. > > +with a user space parser taking care of the conversion to the compact > > +format. > > + > > +Although one might perceive that storing file or metadata digests for a > > +Linux distribution would significantly increase the memory usage, this does > > +not seem to be the case. As an anticipation of the evaluation done in the > > +`Preliminary Performance Evaluation`_ section, protecting binaries and > > +shared libraries of a minimal Fedora 33 installation requires 208K of > > +memory for the digest lists plus 556K for indexing. > > + > > > > +In exchange for a slightly increased memory usage, DIGLIM improves the > > +performance of the integrity subsystem. In the considered scenario, IMA > > +measurement and appraisal with digest lists requires respectively less than > > +one quarter and less than half the time, compared to the current solution. > > I found this paragraph a little bit confusing to understand. Could you > please improve the description? > > I mean: > > what improved by one quarter? > what improved by "less than half of the time"? Ok. I didn't want to make the text too heavy. The tests are described in the Preliminary Performance Evaluation section. > > + > > +DIGLIM also keeps track of whether digest lists have been processed in > some > > +way (e.g. measured or appraised by IMA). This is important for example for > > +remote attestation, so that remote verifiers understand what has been > > +uploaded to the kernel. > > + > > > +DIGLIM behaves like a transactional database, i.e. it has the ability to > > +roll back to the beginning of the transaction if an error occurred during > > +the addition of a digest list (the deletion operation always succeeds). > > I don't think it makes sense to compare it with a transactional database. > > I would say, instead, something like: > > The inserts on DIGLIM are atomic: if an error occurs during the > addition > of a digest list, it rolls back the entire insert operation. Ok, better. > > +This capability has been tested with an ad-hoc fault injection mechanism > > +capable of simulating failures during the operations. > > + > > +Finally, DIGLIM exposes to user space, through securityfs, the digest lists > > +currently loaded, the number of digests added, a query interface and an > > +interface to set digest list labels. > > + > > +[1] LSS EU 2019 > > + > > +- slides: > > + > https://static.sched.com/hosted_files/lsseu2019/bd/secure_attested_commu > nication_channels_lss_eu_2019.pdf > > +- video: https://youtu.be/mffdQgkvDNY > > + > > +[2] FutureTPM EU project, final review meeting demo > > + > > +- slides: > > + https://futuretpm.eu/images/07-3-FutureTPM-Final-Review-Slides-WP6- > Device-Management-Use-Case-HWDU.pdf > > +- video: https://vimeo.com/528251864/4c1d55abcd > > The above won't generate any cross-references with Sphinx. > > For it correct syntax, see: > https://www.sphinx- > doc.org/en/master/usage/restructuredtext/basics.html#citations Ok, will fix it. > > + > > + > > +Binary Integrity > > +---------------- > > + > > +Integrity is a fundamental security property in information systems. > > > +Integrity could be described as the condition in which a generic > > +component is just after it has been released by the entity that created it. > > Sounds a weird description for me. (ISC)2 defines integrity on its > glossary[1] as: > > "Guarding against improper information modification or destruction > and > includes ensuring information non-repudiation and authenticity." > > [1] https://www.isc2.org/Certifications/CISSP/CISSP-Student-Glossary Ok, I meant integrity in the context of trusted computing. https://trustedcomputinggroup.org/wp-content/uploads/IWG_ArchitecturePartII_v1.0.pdf In general the term "integrity" is used to denote the pristine state of a component (page 13). > > +One way to check whether a component is in this condition (called binary > > +integrity) is to calculate its digest and to compare it with a reference > > +value (i.e. the digest calculated in controlled conditions, when the > > +component is released). > > + > > +IMA, a software part of the integrity subsystem, can perform such > > +evaluation and execute different actions: > > + > > +- store the digest in an integrity-protected measurement list, so that it > > + can be sent to a remote verifier for analysis; > > +- compare the calculated digest with a reference value (usually protected > > + with a signature) and deny operations if the file is found corrupted; > > +- store the digest in the system log. > > + > > + > > > > +Contribution > > +------------ > > I would rename this chapter to "Benefits". Ok. > > + > > +DIGLIM further enhances the capabilities offered by IMA-based solutions > > +and, at the same time, makes them more practical to adopt by reusing > > +existing sources as reference values for integrity decisions. > > + > > +Possible sources for digest lists are: > > + > > +- RPM headers; > > +- Debian repository metadata. > > + > > + > > +Benefits for IMA Measurement > > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > + > > +One of the issues that arises when files are measured by the OS is that, > > +due to parallel execution, the order in which file accesses happen cannot > > +be predicted. Since the TPM Platform Configuration Register (PCR) extend > > +operation, executed after each file measurement, cryptographically binds > > +the current measurement to the previous ones, the PCR value at the end of > a > > +workload cannot be predicted too. > > + > > +Thus, even if the usage of a TPM key, bound to a PCR value, should be > > +allowed when only good files were accessed, the TPM could unexpectedly > deny > > +an operation on that key if files accesses did not happen as stated by the > > +key policy (which allows only one of the possible sequences). > > + > > +DIGLIM solves this issue by making the PCR value stable over the time and > > +not dependent on file accesses. The following figure depicts the current > > +and the new approaches: > > + > > +:: > > + > > + IMA measurement list (current) > > + > > + entry# 1st boot 2nd boot 3rd boot > > + +----+---------------+ +----+---------------+ +----+---------------+ > > + 1: | 10 | file1 measur. | | 10 | file3 measur. | | 10 | file2 measur. | > > + +----+---------------+ +----+---------------+ +----+---------------+ > > + 2: | 10 | file2 measur. | | 10 | file2 measur. | | 10 | file3 measur. | > > + +----+---------------+ +----+---------------+ +----+---------------+ > > + 3: | 10 | file3 measur. | | 10 | file1 measur. | | 10 | file4 measur. | > > + +----+---------------+ +----+---------------+ +----+---------------+ > > + > > + PCR: Extend != Extend != Extend > > + file1, file2, file3 file3, file2, file1 file2, file3, file4 > > + > > + > > + PCR Extend definition: > > + > > + PCR(new value) = Hash(Hash(meas. entry), PCR(previous value)) > > + > > +A new entry in the measurement list is created by IMA for each file access. > > +Assuming that ``file1``, ``file2`` and ``file3`` are files provided by the > > +software vendor, ``file4`` is an unknown file, the first two PCR values > > +above represent a good system state, the third a bad system state. The PCR > > +values are the result of the PCR extend operation performed for each > > +measurement entry with the digest of the measurement entry as an input. > > + > > +:: > > + > > + IMA measurement list (with DIGLIM) > > + > > + dlist > > + +--------------+ > > + | header | > > + +--------------+ > > + | file1 digest | > > + | file2 digest | > > + | file3 digest | > > + +--------------+ > > + > > +``dlist`` is a digest list containing the digest of ``file1``, ``file2`` > > +and ``file3``. In the intended scenario, it is generated by a software > > +vendor at the end of the building process, and retrieved by the > > +administrator of the system where the digest list is loaded. > > + > > +:: > > + > > + entry# 1st boot 2nd boot 3rd boot > > + +----+---------------+ +----+---------------+ +----+---------------+ > > + 0: | 11 | dlist measur. | | 11 | dlist measur. | | 11 | dlist measur. | > > + +----+---------------+ +----+---------------+ +----+---------------+ > > + 1: < file1 measur. skip > < file3 measur. skip > < file2 measur. skip > > > + > > + 2: < file2 measur. skip > < file2 measur. skip > < file3 measur. skip > > > + +----+---------------+ > > + 3: < file3 measur. skip > < file1 measur. skip > | 11 | file4 measur. | > > + +----+---------------+ > > + > > + PCR: Extend = Extend != Extend > > + dlist dlist dlist, file4 > > + > > + > > +The first entry in the measurement list contains the digest of the digest > > +list uploaded to the kernel at kernel initialization time. > > + > > +When a file is accessed, IMA queries DIGLIM with the calculated file digest > > +and, if it is found, IMA skips the measurement. > > + > > +Thus, the only information sent to remote verifiers are: the list of > > +files that could possibly be accessed (from the digest list), but not if > > +they were accessed and when; the measurement of unknown files. > > + > > +Despite providing less information, this solution has the advantage that > > +the good system state (i.e. when only ``file1``, ``file2`` and ``file3`` > > +are accessed) now can be represented with a deterministic PCR value (the > > +PCR is extended only with the measurement of the digest list). Also, the > > +bad system state can still be distinguished from the good state (the PCR is > > +extended also with the measurement of ``file4``). > > + > > +If a TPM key is bound to the good PCR value, the TPM would allow the key > to > > +be used if ``file1``, ``file2`` or ``file3`` are accessed, regardless of > > +the sequence in which they are accessed (the PCR value does not change), > > +and would revoke the permission when the unknown ``file4`` is accessed > (the > > +PCR value changes). If a system is able to establish a TLS connection with > > +a peer, this implicitly means that the system was in a good state (i.e. > > +``file4`` was not accessed, otherwise the TPM would have denied the usage > > +of the TPM key due to the key policy). > > + > > + > > +Benefits for IMA Appraisal > > +~~~~~~~~~~~~~~~~~~~~~~~~~~ > > + > > +Extending secure boot to applications means being able to verify the > > +provenance of files accessed. IMA does it by verifying file signatures with > > +a key that it trusts, which requires Linux distribution vendors to > > +additionally include in the package header a signature for each file that > > +must be verified (there is the dedicated ``RPMTAG_FILESIGNATURES`` > section > > +in the RPM header). > > + > > +The proposed approach would be instead to verify data provenance from > > +already available metadata (file digests) in existing packages. IMA would > > +verify the signature of package metadata and search file digests extracted > > +from package metadata and added to the hash table in the kernel. > > + > > +For RPMs, file digests can be found in the ``RPMTAG_FILEDIGESTS`` section > > +of ``RPMTAG_IMMUTABLE``, whose signature is in > ``RPMTAG_RSAHEADER``. For > > +DEBs, file digests (unsafe to use due to a weak digest algorithm) can be > > +found in the ``md5sum`` file, which can be indirectly verified from > > +``Release.gpg``. > > + > > +The following figure highlights the differences between the current and the > > +proposed approach. > > + > > +:: > > + > > + IMA appraisal (current solution, with file signatures): > > + > > + appraise > > + +-----------+ > > + V | > > + +-------------------------+-----+ +-------+-----+ | > > + | RPM header | | ima rpm | file1 | sig | | > > + | ... | | plugin +-------+-----+ +-----+ > > + | file1 sig [to be added] | sig |--------> ... | IMA | > > + | ... | | +-------+-----+ +-----+ > > + | fileN sig [to be added] | | | fileN | sig | > > + +-------------------------+-----+ +-------+-----+ > > + > > +In this case, file signatures must be added to the RPM header, so that the > > +``ima`` rpm plugin can extract them together with the file content. The > RPM > > +header signature is not used. > > + > > +:: > > + > > + IMA appraisal (with DIGLIM): > > + > > + kernel hash table > > + with RPM header content > > + +---+ +--------------+ > > + | |--->| file1 digest | > > + +---+ +--------------+ > > + ... > > + +---+ appraise (file1) > > + | | <--------------+ > > + +----------------+-----+ +---+ | > > + | RPM header | | ^ | > > + | ... | | digest_list | | > > + | file1 digest | sig | rpm plugin | +-------+ +-----+ > > + | ... | |-------------+--->| file1 | | IMA | > > + | fileN digest | | +-------+ +-----+ > > + +----------------+-----+ | > > + ^ | > > + +------------------------------------+ > > + appraise (RPM header) > > + > > +In this case, the RPM header is used as it is, and its signature is used > > +for IMA appraisal. Then, the ``digest_list`` rpm plugin executes the user > > +space parser to parse the RPM header and add the extracted digests to an > > +hash table in the kernel. IMA appraisal of the files in the RPM package > > +consists in searching their digest in the hash table. > > + > > +Other than reusing available information as digest list, another advantage > > +is the lower computational overhead compared to the solution with file > > +signatures (only one signature verification for many files and digest > > +lookup, instead of per file signature verification, see `Preliminary > > +Performance Evaluation`_ for more details). > > + > > + > > +Lifecycle > > +--------- > > + > > +The lifecycle of DIGLIM is represented in the following figure: > > + > > +:: > > You could just use: > > The lifecycle of DIGLIM is represented in the following figure:: > > > + > > + Vendor premises (release process with modifications): > > + > > + +------------+ +-----------------------+ +------------------------+ > > + | 1. build a | | 2. generate and sign | | 3. publish the package | > > + | package |-->| a digest list from |-->| and digest list in | > > + | | | packaged files | | a repository | > > + +------------+ +-----------------------+ +------------------------+ > > + | > > + | > > + User premises: | > > + V > > + +---------------------+ +------------------------+ +-----------------+ > > + | 6. use digest lists | | 5. download the digest | | 4. download and | > > + | for measurement |<--| list and upload to |<--| install the | > > + | and/or appraisal | | the kernel | | package | > > + +---------------------+ +------------------------+ +-----------------+ > > + > > +The figure above represents all the steps when a digest list is > > +generated separately. However, as mentioned in `Contribution`_, in most > > +cases existing packages can be already used as a source for digest lists, > > +limiting the effort for software vendors. > > + > > +If, for example, RPMs are used as a source for digest lists, the figure > > +above becomes: > > + > > +:: > > Same here. Ok. Thanks Roberto HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Li Peng, Li Jian, Shi Yanli > > + > > + Vendor premises (release process without modifications): > > + > > + +------------+ +------------------------+ > > + | 1. build a | | 2. publish the package | > > + | package |-->| in a repository |---------------------+ > > + | | | | | > > + +------------+ +------------------------+ | > > + | > > + | > > + User premises: | > > + V > > + +---------------------+ +------------------------+ +-----------------+ > > + | 5. use digest lists | | 4. extract digest list | | 3. download and | > > + | for measurement |<--| from the package |<--| install the | > > + | and/or appraisal | | and upload to the | | package | > > + | | | kernel | | | > > + +---------------------+ +------------------------+ +-----------------+ > > + > > +Step 4 can be performed with the ``digest_list`` rpm plugin and the user > > +space parser, without changes to rpm itself. > > + > > + > > +Security Assumptions > > +-------------------- > > + > > +As mentioned in the `Introduction`_, DIGLIM will be primarily used in > > +conjunction with IMA to enforce a mandatory policy on all user space > > +processes, including those owned by root. Even root, in a system with a > > +locked-down kernel, cannot affect the enforcement of the mandatory > policy > > +or, if changes are permitted, it cannot do so without being detected. > > + > > +Given that the target of the enforcement are user space processes, DIGLIM > > +cannot be placed in the target, as a Mandatory Access Control (MAC) > design > > +is required to have the components responsible to enforce the mandatory > > +policy separated from the target. > > + > > +While locking-down a system and limiting actions with a mandatory policy > is > > +generally perceived by users as an obstacle, it has noteworthy benefits for > > +the users themselves. > > + > > +First, it would timely block attempts by malicious software to steal or > > +misuse user assets. Although users could query the package managers to > > +detect them, detection would happen after the fact, or it wouldn't happen > > +at all if the malicious software tampered with package managers. With a > > +mandatory policy enforced by the kernel, users would still be able to > > +decide which software they want to be executed except that, unlike > package > > +managers, the kernel is not affected by user space processes or root. > > + > > +Second, it might make systems more easily verifiable from outside, due to > > +the limited actions the system allows. When users connect to a server, not > > +only they would be able to verify the server identity, which is already > > +possible with communication protocols like TLS, but also if the software > > +running on that server can be trusted to handle their sensitive data. > > + > > + > > +Adoption > > +-------- > > + > > +A former version of DIGLIM is used in the following OSes: > > + > > +- openEuler 20.09 > > + https://github.com/openeuler-mirror/kernel/tree/openEuler-20.09 > > + > > +- openEuler 21.03 > > + https://github.com/openeuler-mirror/kernel/tree/openEuler-21.03 > > + > > +Originally, DIGLIM was part of IMA (known as IMA Digest Lists). In this > > +version, it has been redesigned as a standalone module with an API that > > +makes its functionality accessible by IMA and, eventually, other > > +subsystems. > > + > > +User Space Support > > +------------------ > > + > > +Digest lists can be generated and managed with ``digest-list-tools``: > > + > > +https://github.com/openeuler-mirror/digest-list-tools > > + > > +It includes two main applications: > > + > > +- ``gen_digest_lists``: generates digest lists from files in the > > + filesystem or from the RPM database (more digest list sources can be > > + supported); > > +- ``manage_digest_lists``: converts and uploads digest lists to the > > + kernel. > > + > > +Integration with rpm is done with the ``digest_list`` plugin: > > + > > +https://gitee.com/src-openeuler/rpm/blob/master/Add-digest-list- > plugin.patch > > + > > +This plugin writes the RPM header and its signature to a file, so that the > > +file is ready to be appraised by IMA, and calls the user space parser to > > +convert and upload the digest list to the kernel. > > + > > + > > +Simple Usage Example (Tested with Fedora 33) > > +-------------------------------------------- > > + > > +1. Digest list generation (RPM headers and their signature are copied to > > + the specified directory): > > + > > +.. code-block:: bash > > + > > + # mkdir /etc/digest_lists > > + # gen_digest_lists -t file -f rpm+db -d /etc/digest_lists -o add > > + > > +2. Digest list upload with the user space parser: > > + > > +.. code-block:: bash > > + > > + # manage_digest_lists -p add-digest -d /etc/digest_lists > > + > > +3. First digest list query: > > + > > +.. code-block:: bash > > + > > + # echo sha256-$(sha256sum /bin/cat) > > /sys/kernel/security/integrity/diglim/digest_query > > + # cat /sys/kernel/security/integrity/diglim/digest_query > > + sha256-[...]-0-file_list-rpm-coreutils-8.32-18.fc33.x86_64 (actions: 0): > version: 1, algo: sha256, type: 2, modifiers: 1, count: 106, datalen: 3392 > > + > > +4. Second digest list query: > > + > > +.. code-block:: bash > > + > > + # echo sha256-$(sha256sum /bin/zip) > > /sys/kernel/security/integrity/diglim/digest_query > > + # cat /sys/kernel/security/integrity/diglim/digest_query > > + sha256-[...]-0-file_list-rpm-zip-3.0-27.fc33.x86_64 (actions: 0): version: 1, > algo: sha256, type: 2, modifiers: 1, count: 4, datalen: 128 > > + > > + > > +Preliminary Performance Evaluation > > +---------------------------------- > > + > > +This section provides an initial estimation of the overhead introduced by > > +DIGLIM. The estimation has been performed on a Fedora 33 virtual machine > > +with 1447 packages installed. The virtual machine has 16 vCPU (host CPU: > > +AMD Ryzen Threadripper PRO 3955WX 16-Cores) and 2G of RAM (host > memory: > > +64G). The virtual machine also has a vTPM with libtpms and swtpm as > > +backend. > > + > > +After writing the RPM headers to files, the size of the directory > > +containing them is 36M. > > + > > +After converting the RPM headers to the compact digest list, the size of > > +the data being uploaded to the kernel is 3.6M. > > + > > +The time to load the entire RPM database is 0.628s. > > + > > +After loading the digest lists to the kernel, the slab usage due to > > +indexing is (obtained with slab_nomerge in the kernel command line): > > + > > +:: > > + > > + OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME > > + 118144 118144 100% 0,03K 923 128 3692K > digest_list_item_ref_cache > > + 102400 102400 100% 0,03K 800 128 3200K digest_item_cache > > + 2646 2646 100% 0,09K 63 42 252K digest_list_item_cache > > + > > +The stats, obtained from the ``digests_count`` interface, introduced later, > > +are: > > + > > +:: > > + > > + Parser digests: 0 > > + File digests: 99100 > > + Metadata digests: 0 > > + Digest list digests: 1423 > > + > > +On this installation, this would be the worst case in which all files are > > +measured and/or appraised, which is currently not recommended without > > +enforcing an integrity policy protecting mutable files. Infoflow LSM is a > > +component to accomplish this task: > > + > > +https://patchwork.kernel.org/project/linux- > integrity/cover/20190818235745.1417-1-roberto.sassu@huawei.com/ > > + > > +The first manageable goal of IMA with DIGLIM is to use an execution policy, > > +with measurement and/or appraisal of files executed or mapped in memory > as > > +executable (in addition to kernel modules and firmware). In this > > +case, the digest list contains the digest only for those files. The numbers > > +above change as follows. > > + > > +After converting the RPM headers to the compact digest list, the size of > > +the data being uploaded to the kernel is 208K. > > + > > +The time to load the digest of binaries and shared libraries is 0.062s. > > + > > +After loading the digest lists to the kernel, the slab usage due to > > +indexing is: > > + > > +:: > > + > > + OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME > > + 7168 7168 100% 0,03K 56 128 224K digest_list_item_ref_cache > > + 7168 7168 100% 0,03K 56 128 224K digest_item_cache > > + 1134 1134 100% 0,09K 27 42 108K digest_list_item_cache > > + > > + > > +The stats, obtained from the ``digests_count`` interface, are: > > + > > +:: > > + > > + Parser digests: 0 > > + File digests: 5986 > > + Metadata digests: 0 > > + Digest list digests: 1104 > > + > > + > > +Comparison with IMA > > +~~~~~~~~~~~~~~~~~~~ > > + > > +This section compares the performance between the current solution for > IMA > > +measurement and appraisal, and IMA with DIGLIM. > > + > > + > > +Workload A (without DIGLIM): > > + > > +#. cat file[0-5985] > /dev/null > > + > > + > > +Workload B (with DIGLIM): > > + > > +#. echo $PWD/0-file_list-compact-file[0-1103] > > <securityfs>/integrity/diglim/digest_list_add > > +#. cat file[0-5985] > /dev/null > > + > > + > > +Workload A execution time without IMA policy: > > + > > +:: > > + > > + real 0m0,155s > > + user 0m0,008s > > + sys 0m0,066s > > + > > + > > +Measurement > > +........... > > + > > +IMA policy: > > + > > +:: > > + > > + measure fowner=2000 func=FILE_CHECK mask=MAY_READ > use_diglim=allow pcr=11 ima_template=ima-sig > > + > > +``use_diglim`` is a policy keyword not yet supported by IMA. > > + > > + > > +Workload A execution time with IMA and 5986 files with signature > measured: > > + > > +:: > > + > > + real 0m8,273s > > + user 0m0,008s > > + sys 0m2,537s > > + > > + > > +Workload B execution time with IMA, 1104 digest lists with signature > > +measured and uploaded to the kernel, and 5986 files with signature > accessed > > +but not measured (due to the file digest being found in the hash table): > > + > > +:: > > + > > + real 0m1,837s > > + user 0m0,036s > > + sys 0m0,583s > > + > > + > > +Appraisal > > +......... > > + > > +IMA policy: > > + > > +:: > > + > > + appraise fowner=2000 func=FILE_CHECK mask=MAY_READ > use_diglim=allow > > + > > +``use_diglim`` is a policy keyword not yet supported by IMA. > > + > > + > > +Workload A execution time with IMA and 5986 files with file signature > > +appraised: > > + > > +:: > > + > > + real 0m2,197s > > + user 0m0,011s > > + sys 0m2,022s > > + > > + > > +Workload B execution time with IMA, 1104 digest lists with signature > > +appraised and uploaded to the kernel, and with 5986 files with signature > > +not verified (due to the file digest being found in the hash table): > > + > > +:: > > + > > + real 0m0,982s > > + user 0m0,020s > > + sys 0m0,865s > > diff --git a/Documentation/security/index.rst > b/Documentation/security/index.rst > > index 16335de04e8c..6c3aea41c55b 100644 > > --- a/Documentation/security/index.rst > > +++ b/Documentation/security/index.rst > > @@ -17,3 +17,4 @@ Security Documentation > > tpm/index > > digsig > > landlock > > + diglim/index > > diff --git a/MAINTAINERS b/MAINTAINERS > > index 6c8be735cc91..c914dadd7e65 100644 > > --- a/MAINTAINERS > > +++ b/MAINTAINERS > > @@ -5452,6 +5452,15 @@ L: linux-gpio@vger.kernel.org > > S: Maintained > > F: drivers/gpio/gpio-gpio-mm.c > > > > +DIGLIM > > +M: Roberto Sassu <roberto.sassu@huawei.com> > > +L: linux-integrity@vger.kernel.org > > +S: Supported > > +T: git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity.git > > +F: Documentation/security/diglim/architecture.rst > > +F: Documentation/security/diglim/index.rst > > +F: Documentation/security/diglim/introduction.rst > > + > > DIOLAN U2C-12 I2C DRIVER > > M: Guenter Roeck <linux@roeck-us.net> > > L: linux-i2c@vger.kernel.org > > > > Thanks, > Mauro
Em Mon, 26 Jul 2021 18:36:52 +0200 Roberto Sassu <roberto.sassu@huawei.com> escreveu: > Introduce the methods requires to manage the three objects defined. > > - digest_item methods: > - digest_add() > - digest_del() > - __digest_lookup() > - diglim_digest_get_info() > > - digest_list_item_ref methods: > - digest_list_ref_add() > - digest_list_ref_del() > > - digest_list_item methods: > - digest_list_add() > - digest_list_del() > > More information about these functions can be found in > Documentation/security/diglim/implementation.rst. > > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com> > --- > .../security/diglim/implementation.rst | 9 + > MAINTAINERS | 2 + > include/linux/diglim.h | 28 + > security/integrity/Kconfig | 1 + > security/integrity/Makefile | 1 + > security/integrity/diglim/Kconfig | 11 + > security/integrity/diglim/Makefile | 8 + > security/integrity/diglim/diglim.h | 20 +- > security/integrity/diglim/methods.c | 499 ++++++++++++++++++ > 9 files changed, 578 insertions(+), 1 deletion(-) > create mode 100644 include/linux/diglim.h > create mode 100644 security/integrity/diglim/Kconfig > create mode 100644 security/integrity/diglim/Makefile > create mode 100644 security/integrity/diglim/methods.c > > diff --git a/Documentation/security/diglim/implementation.rst b/Documentation/security/diglim/implementation.rst > index 6002049612a1..54af23b2f5f1 100644 > --- a/Documentation/security/diglim/implementation.rst > +++ b/Documentation/security/diglim/implementation.rst > @@ -200,3 +200,12 @@ Similarly: > the digest can be obtained by summing the address of the digest list buffer > with ``digest_offset`` (except for the digest lists, where the digest is > stored in the ``digest`` field of the ``digest_list_item`` structure). > + > + > +Methods > +------- > + > +This section introduces the methods requires to manage the three objects > +defined. > + > +.. kernel-doc:: security/integrity/diglim/methods.c > diff --git a/MAINTAINERS b/MAINTAINERS > index f7592d41367d..9e085a36654a 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -5461,8 +5461,10 @@ F: Documentation/security/diglim/architecture.rst > F: Documentation/security/diglim/implementation.rst > F: Documentation/security/diglim/index.rst > F: Documentation/security/diglim/introduction.rst > +F: include/linux/diglim.h > F: include/uapi/linux/diglim.h > F: security/integrity/diglim/diglim.h > +F: security/integrity/diglim/methods.c > > DIOLAN U2C-12 I2C DRIVER > M: Guenter Roeck <linux@roeck-us.net> > diff --git a/include/linux/diglim.h b/include/linux/diglim.h > new file mode 100644 > index 000000000000..d4b4548a288b > --- /dev/null > +++ b/include/linux/diglim.h > @@ -0,0 +1,28 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +/* > + * Copyright (C) 2017-2021 Huawei Technologies Duesseldorf GmbH > + * > + * Author: Roberto Sassu <roberto.sassu@huawei.com> > + * > + * DIGLIM functions available for use by kernel subsystems. > + */ > + > +#ifndef __DIGLIM_H > +#define __DIGLIM_H > + > +#include <crypto/hash_info.h> > +#include <uapi/linux/diglim.h> > + > +#ifdef CONFIG_DIGLIM > +extern int diglim_digest_get_info(u8 *digest, enum hash_algo algo, > + enum compact_types type, u16 *modifiers, > + u8 *actions); > +#else > +static inline int diglim_digest_get_info(u8 *digest, enum hash_algo algo, > + enum compact_types type, > + u16 *modifiers, u8 *actions) > +{ > + return -ENOENT; > +} > +#endif /*CONFIG_DIGLIM*/ > +#endif /*__DIGLIM_H*/ > diff --git a/security/integrity/Kconfig b/security/integrity/Kconfig > index 71f0177e8716..8f94f4dcc052 100644 > --- a/security/integrity/Kconfig > +++ b/security/integrity/Kconfig > @@ -98,5 +98,6 @@ config INTEGRITY_AUDIT > > source "security/integrity/ima/Kconfig" > source "security/integrity/evm/Kconfig" > +source "security/integrity/diglim/Kconfig" > > endif # if INTEGRITY > diff --git a/security/integrity/Makefile b/security/integrity/Makefile > index 7ee39d66cf16..d6166550a6b8 100644 > --- a/security/integrity/Makefile > +++ b/security/integrity/Makefile > @@ -19,3 +19,4 @@ integrity-$(CONFIG_LOAD_PPC_KEYS) += platform_certs/efi_parser.o \ > platform_certs/keyring_handler.o > obj-$(CONFIG_IMA) += ima/ > obj-$(CONFIG_EVM) += evm/ > +obj-$(CONFIG_DIGLIM) += diglim/ > diff --git a/security/integrity/diglim/Kconfig b/security/integrity/diglim/Kconfig > new file mode 100644 > index 000000000000..436a76a14337 > --- /dev/null > +++ b/security/integrity/diglim/Kconfig > @@ -0,0 +1,11 @@ > +# SPDX-License-Identifier: GPL-2.0-only > +# Digest Lists Integrity Module (DIGLIM) > +# > +config DIGLIM > + bool "Digest Lists Integrity Module (DIGLIM)" > + select SECURITYFS > + select CRYPTO > + select CRYPTO_HASH_INFO > + help > + DIGLIM provides reference values for file content and metadata, > + that can be used for measurement and appraisal with IMA. > diff --git a/security/integrity/diglim/Makefile b/security/integrity/diglim/Makefile > new file mode 100644 > index 000000000000..b761ed8cfb3e > --- /dev/null > +++ b/security/integrity/diglim/Makefile > @@ -0,0 +1,8 @@ > +# SPDX-License-Identifier: GPL-2.0 > +# > +# Makefile for building Digest Lists Integrity Module (DIGLIM). > +# > + > +obj-$(CONFIG_DIGLIM) += diglim.o > + > +diglim-y := methods.o > diff --git a/security/integrity/diglim/diglim.h b/security/integrity/diglim/diglim.h > index 578253d7e1d1..25851e7d4906 100644 > --- a/security/integrity/diglim/diglim.h > +++ b/security/integrity/diglim/diglim.h > @@ -20,7 +20,7 @@ > #include <linux/audit.h> > #include <crypto/hash_info.h> > #include <linux/hash_info.h> > -#include <uapi/linux/diglim.h> > +#include <linux/diglim.h> > > #define MAX_DIGEST_SIZE 64 > #define HASH_BITS 10 > @@ -81,6 +81,8 @@ static inline unsigned int hash_key(u8 *digest) > return (digest[0] | digest[1] << 8) % DIGLIM_HTABLE_SIZE; > } > > +extern struct h_table htable[COMPACT__LAST]; > + it sounds somewhat risky to use just "htable" for a var declared as external. > static inline struct compact_list_hdr *get_hdr( > struct digest_list_item *digest_list, > loff_t hdr_offset) > @@ -131,4 +133,20 @@ static inline u8 *get_digest_ref(struct digest_list_item_ref *ref) > > return ref->digest_list->buf + ref->digest_offset; > } > + > +struct digest_item *__digest_lookup(u8 *digest, enum hash_algo algo, > + enum compact_types type, u16 *modifiers, > + u8 *actions); > +struct digest_item *digest_add(u8 *digest, enum hash_algo algo, > + enum compact_types type, > + struct digest_list_item *digest_list, > + loff_t digest_offset, loff_t hdr_offset); > +void digest_del(u8 *digest, enum hash_algo algo, enum compact_types type, > + struct digest_list_item *digest_list, loff_t digest_offset, > + loff_t hdr_offset); > +struct digest_item *digest_list_add(u8 *digest, enum hash_algo algo, > + loff_t size, u8 *buf, u8 actions, > + const char *label); > +void digest_list_del(u8 *digest, enum hash_algo algo, u8 actions, > + struct digest_list_item *digest_list); > #endif /*__DIGLIM_INTERNAL_H*/ > diff --git a/security/integrity/diglim/methods.c b/security/integrity/diglim/methods.c > new file mode 100644 > index 000000000000..7ed61399cfe8 > --- /dev/null > +++ b/security/integrity/diglim/methods.c > @@ -0,0 +1,499 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * Copyright (C) 2005,2006,2007,2008 IBM Corporation > + * Copyright (C) 2017-2021 Huawei Technologies Duesseldorf GmbH > + * > + * Author: Roberto Sassu <roberto.sassu@huawei.com> > + * > + * Functions to manage digest lists. > + */ > + > +#include <linux/vmalloc.h> > +#include <linux/module.h> > +#include <linux/fault-inject.h> > + > +#include "diglim.h" > +#include "../integrity.h" > + > +/* Define a cache for each object type. */ > +static struct kmem_cache *digest_list_item_cache __read_mostly; > +static struct kmem_cache *digest_list_item_ref_cache __read_mostly; > +static struct kmem_cache *digest_item_cache __read_mostly; > + > +/* Define a hash table for each digest type. */ > +struct h_table htable[COMPACT__LAST] = {{ > + .queue[0 ... DIGLIM_HTABLE_SIZE - 1] = HLIST_HEAD_INIT > +}}; > + > +#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS > +static DECLARE_FAULT_ATTR(fail_diglim); > + > +static int __init fail_diglim_debugfs(void) > +{ > + struct dentry *dir = fault_create_debugfs_attr("fail_diglim", NULL, > + &fail_diglim); > + > + return PTR_ERR_OR_ZERO(dir); > +} > + > +static inline bool should_fail_diglim(void) > +{ > + return should_fail(&fail_diglim, 1); > +} > + > +late_initcall(fail_diglim_debugfs); > +#else > +static inline bool should_fail_diglim(void) > +{ > + return false; > +} > +#endif I guess this is a matter of personal preference, but, IMO, it is a lot better to place the debugfs stuff on a separate source file, avoiding ugly #ifdefs in the middle of the code. Ok, the current code is too small to deserve a separate file, but if later patches would add more stuff, then I would opt to have this on a separate file. > + > +/** > + * __digest_lookup - lookup digest and return associated modifiers and actions > + * @digest: digest to lookup > + * @algo: digest algorithm > + * @type: type of digest to lookup (e.g. file, metadata) > + * @modifiers: modifiers (attributes) associated to the found digest > + * @actions: actions performed by IMA on the digest list containing the digest > + * > + * This function searches the given digest in the hash table depending on the > + * passed type and sets the modifiers and actions associated to the digest, if > + * the pointers are not NULL. > + * > + * This function is not intended for external use, as the returned digest item > + * could be freed at any time after it has been returned. > + * diglim_digest_get_info() should be used instead by external callers, as it > + * only returns the modifiers and the actions associated to the digest at the > + * time the digest is searched. > + * > + * RCU protects both the hash table and the linked list of references to the > + * digest lists containing the found digest. > + * > + * Return: a digest_item structure if the digest is found, NULL otherwise. > + */ > +struct digest_item *__digest_lookup(u8 *digest, enum hash_algo algo, > + enum compact_types type, u16 *modifiers, > + u8 *actions) > +{ > + struct digest_item *d = NULL; > + struct digest_list_item_ref *ref; > + int digest_len = hash_digest_size[algo]; > + unsigned int key = hash_key(digest); > + bool found = false; > + > + rcu_read_lock(); > + hlist_for_each_entry_rcu(d, &htable[type].queue[key], hnext) { > + list_for_each_entry_rcu(ref, &d->refs, list) { > + if (get_algo_ref(ref) != algo || > + memcmp(get_digest_ref(ref), digest, digest_len)) > + break; > + > + found = true; > + > + /* There is no need to scan all digest list refs. */ > + if (!modifiers || !actions) > + break; > + > + /* > + * The resulting modifiers and actions are the OR of the > + * modifiers and actions for each digest list. > + */ > + *modifiers |= get_hdr_ref(ref)->modifiers; > + *actions |= ref->digest_list->actions; > + } > + > + if (found) > + break; > + } > + > + rcu_read_unlock(); > + return d; > +} > + > +/** > + * diglim_digest_get_info - lookup digest and return modifiers and actions > + * @digest: digest to lookup > + * @algo: digest algorithm > + * @type: type of digest to lookup (e.g. file, metadata) > + * @modifiers: modifiers (attributes) associated to the found digest > + * @actions: actions performed by IMA on the digest lists containing the digest > + * > + * This function searches the given digest in the hash table depending on the > + * passed type and sets the modifiers and actions associated to the digest, if > + * the pointers are not NULL. > + * > + * This function is safe for external use, as it does not return pointers of > + * objects that can be freed without the caller notices it. > + * > + * Return: 0 if the digest is found, -ENOENT otherwise. > + */ > +int diglim_digest_get_info(u8 *digest, enum hash_algo algo, > + enum compact_types type, u16 *modifiers, u8 *actions) > +{ > + struct digest_item *d; > + > + d = __digest_lookup(digest, algo, type, modifiers, actions); > + if (!d) > + return -ENOENT; > + > + return 0; > +} > + > +/** > + * digest_list_ref_add - add reference to a digest list > + * @d: digest a new reference is added to > + * @digest_list: digest list whose reference is being added > + * @digest_offset: offset of the digest in the buffer of the digest list > + * @hdr_offset: offset of the header within the digest list the digest refers to > + * > + * This function adds a new reference to an existing digest list for a given > + * digest. The reference is described by the digest_list_item_ref structure and > + * consists of a pointer of the digest list, the offset of the digest to the > + * beginning of the digest list buffer and the offset of the header the digest > + * refers to (each digest list might be composed of several digest blocks, each > + * prefixed by a header describing the attributes of those digests). > + * > + * Return: 0 if a new digest list reference was successfully added, a negative > + * value otherwise. > + */ > +static int digest_list_ref_add(struct digest_item *d, > + struct digest_list_item *digest_list, > + loff_t digest_offset, loff_t hdr_offset) > +{ > + struct digest_list_item_ref *new_ref = NULL; > + u8 *digest = get_digest(digest_list, digest_offset, hdr_offset); > + enum hash_algo algo = get_algo(digest_list, digest_offset, hdr_offset); > + int digest_len = hash_digest_size[algo]; > + > + /* Allocate a new reference. */ > + if (!should_fail_diglim()) > + new_ref = kmem_cache_alloc(digest_list_item_ref_cache, > + GFP_KERNEL); > + if (!new_ref) { > + print_hex_dump(KERN_ERR, "digest list ref allocation failed: ", > + DUMP_PREFIX_NONE, digest_len, 1, digest, > + digest_len, true); > + return -ENOMEM; > + } > + > + /* Set the new reference. */ > + new_ref->digest_list = digest_list; > + /* Converting loff_t -> u32 is fine as long as the digest list < 4G. */ > + new_ref->digest_offset = digest_offset; > + new_ref->hdr_offset = hdr_offset; > + > + list_add_tail_rcu(&new_ref->list, &d->refs); > + > + print_hex_dump_debug("add digest list ref: ", DUMP_PREFIX_NONE, > + digest_len, 1, digest, digest_len, true); > + return 0; > +} > + > +/** > + * digest_list_ref_del - del reference to a digest list > + * @d: digest a reference is deleted from > + * @digest_list: digest list whose reference is being deleted > + * @digest_offset: offset of the digest in the buffer of the digest list > + * @hdr_offset: offset of the header within the digest list the digest refers to > + * > + * This function searches the reference to an already loaded digest list in the > + * linked list of references stored for each digest item. If the reference is > + * found (if not, it is a bug), the function deletes it from the linked list. > + */ > +static void digest_list_ref_del(struct digest_item *d, > + struct digest_list_item *digest_list, > + loff_t digest_offset, loff_t hdr_offset) > +{ > + struct digest_list_item_ref *ref; > + u8 *digest = get_digest(digest_list, digest_offset, hdr_offset); > + enum hash_algo algo = get_algo(digest_list, digest_offset, hdr_offset); > + int digest_len = hash_digest_size[algo]; > + > + /* Search for a digest list reference. */ > + list_for_each_entry(ref, &d->refs, list) > + if (ref->digest_list == digest_list) > + break; > + > + if (!ref) { > + print_hex_dump(KERN_ERR, "digest list ref not found: ", > + DUMP_PREFIX_NONE, digest_len, 1, digest, > + digest_len, true); > + return; > + } > + > + list_del_rcu(&ref->list); > + kmem_cache_free(digest_list_item_ref_cache, ref); > + > + print_hex_dump_debug("del digest list ref: ", DUMP_PREFIX_NONE, > + digest_len, 1, digest, digest_len, true); > +} > + > +/** > + * digest_add - add a new digest > + * @digest: digest in binary form > + * @algo: digest algorithm > + * @type: digest type > + * @digest_list: digest list the new digest belongs to > + * @digest_offset: offset of the digest in the buffer of the digest list > + * @hdr_offset: offset of the header within the digest list the digest refers to > + * > + * This function first searches if the digest is already in the hash table for > + * the given type. The digest is searched by comparing the passed digest and > + * algorithm with the digest obtained from the first digest list reference > + * (buffer + digest_offset), or from the digest field of a digest list item, > + * for a digest list. > + * > + * If the digest exists, only a new reference is added (there might be multiple > + * references to the same digest list). > + * > + * If the digest is not found, a new digest item is allocated and a reference to > + * the passed digest list is added to that item. The digest item is finally > + * added to the hash table for the given type. > + * > + * Proper locking must be provided by the caller. > + * > + * Return: a new or the found digest item on success, an error pointer > + * otherwise. > + */ > +struct digest_item *digest_add(u8 *digest, enum hash_algo algo, > + enum compact_types type, > + struct digest_list_item *digest_list, > + loff_t digest_offset, loff_t hdr_offset) > +{ > + int digest_len = hash_digest_size[algo]; > + struct digest_item *d; > + int ret; > + > + /* Search the digest. */ > + d = __digest_lookup(digest, algo, type, NULL, NULL); > + if (d) { > + /* > + * Add a new digest list reference to the existing digest item. > + */ > + ret = digest_list_ref_add(d, digest_list, digest_offset, > + hdr_offset); > + if (ret < 0) > + return ERR_PTR(ret); > + > + print_hex_dump_debug("digest add duplicate: ", DUMP_PREFIX_NONE, > + digest_len, 1, digest, digest_len, true); > + return d; > + } > + > + /* Allocate a new digest item. */ > + if (!should_fail_diglim()) > + d = kmem_cache_alloc(digest_item_cache, GFP_KERNEL); > + if (!d) { > + print_hex_dump_debug("digest allocation failed: ", > + DUMP_PREFIX_NONE, digest_len, 1, digest, > + digest_len, true); > + return ERR_PTR(-ENOMEM); > + } > + > + INIT_LIST_HEAD(&d->refs); > + > + /* Add a new digest list reference to the new digest item. */ > + ret = digest_list_ref_add(d, digest_list, digest_offset, hdr_offset); > + if (ret < 0) { > + kmem_cache_free(digest_item_cache, d); > + return ERR_PTR(ret); > + } > + > + /* Add the new digest item to the hash table for the given type. */ > + hlist_add_head_rcu(&d->hnext, &htable[type].queue[hash_key(digest)]); > + htable[type].len++; > + > + print_hex_dump_debug("digest add: ", DUMP_PREFIX_NONE, digest_len, 1, > + digest, digest_len, true); > + return d; > +} > + > +/** > + * digest_del - delete a digest with one reference, or just a reference > + * @digest: digest in binary form > + * @algo: digest algorithm > + * @type: digest type > + * @digest_list: digest list the digest belongs to > + * @digest_offset: offset of the digest in the buffer of the digest list > + * @hdr_offset: offset of the header within the digest list the digest refers to > + * > + * This function is called when a digest list is being removed. The digest is > + * first searched in the hash table for the given type. If it is found (if not, > + * it is a bug, because digest lists can be deleted only if they were added > + * previously), a reference of the passed digest list is deleted from the linked > + * list of references of the digest item. > + * > + * If the last reference was deleted, the digest item is also deleted and > + * removed from the hash table. > + * > + * Proper locking must be provided by the caller. > + */ > +void digest_del(u8 *digest, enum hash_algo algo, enum compact_types type, > + struct digest_list_item *digest_list, loff_t digest_offset, > + loff_t hdr_offset) > +{ > + struct digest_item *d; > + int digest_len = hash_digest_size[algo]; > + > + /* Search the digest. */ > + d = __digest_lookup(digest, algo, type, NULL, NULL); > + if (!d) { > + print_hex_dump(KERN_ERR, "digest not found: ", DUMP_PREFIX_NONE, > + digest_len, 1, digest, digest_len, true); > + return; > + } > + > + /* Delete a reference of the passed digest list. */ > + digest_list_ref_del(d, digest_list, digest_offset, hdr_offset); > + > + print_hex_dump_debug(!list_empty(&d->refs) ? > + "digest del duplicate: " : "digest del: ", > + DUMP_PREFIX_NONE, digest_len, 1, digest, > + digest_len, true); > + > + /* Return if there are still references. */ > + if (!list_empty(&d->refs)) > + return; > + > + /* > + * Remove the digest item from the hash table and free it if there are > + * no more references left. > + */ > + hlist_del_rcu(&d->hnext); > + htable[type].len--; > + kmem_cache_free(digest_item_cache, d); > +} > + > +/** > + * digest_list_add - add a new digest list > + * @digest: digest of the digest list in binary form > + * @algo: digest algorithm > + * @size: digest list size > + * @buf: digest list buffer > + * @actions: actions (measure/appraise) performed by IMA on the digest list > + * @label: label to be used to identify the digest list > + * > + * This function allocates a new digest list item, which contains the buffer, > + * size, actions performed by IMA and a label. Each digest list item is > + * associated to a digest item representing the digest of the digest list. > + * > + * This function prevents the same digest list to be added multiple times by > + * searching its digest in the hash table for the COMPACT_DIGEST_LIST type. > + * > + * The passed buffer is copied in a new memory area, to avoid to reference > + * memory that could be freed by the caller. > + * > + * If allocation of a new digest list and the associated buffer was successful, > + * its digest is added to the hash table for the COMPACT_DIGEST_LIST type. > + * > + * Proper locking must be provided by the caller. > + * > + * Return: the digest item associated to the digest list item on success, an > + * error pointer otherwise. > + */ > +struct digest_item *digest_list_add(u8 *digest, enum hash_algo algo, > + loff_t size, u8 *buf, u8 actions, > + const char *label) > +{ > + struct digest_item *d; > + struct digest_list_item *digest_list = NULL; > + int digest_len = hash_digest_size[algo]; > + > + /* Search the digest of the digest list. */ > + d = __digest_lookup(digest, algo, COMPACT_DIGEST_LIST, NULL, NULL); > + if (d) { > + print_hex_dump(KERN_ERR, "digest list already uploaded: ", > + DUMP_PREFIX_NONE, digest_len, 1, digest, > + digest_len, true); > + return ERR_PTR(-EEXIST); > + } > + > + /* Allocate a new digest list. */ > + if (!should_fail_diglim()) > + digest_list = kmem_cache_alloc(digest_list_item_cache, > + GFP_KERNEL); > + if (!digest_list) { > + print_hex_dump(KERN_ERR, "digest list allocation failed: ", > + DUMP_PREFIX_NONE, digest_len, 1, digest, > + digest_len, true); > + return ERR_PTR(-ENOMEM); > + } > + > + digest_list->buf = NULL; > + digest_list->size = size; > + > + if (!should_fail_diglim()) > + digest_list->buf = kmemdup(buf, size, GFP_KERNEL); > + if (!digest_list->buf) { > + print_hex_dump(KERN_ERR, "digest list allocation failed: ", > + DUMP_PREFIX_NONE, digest_len, 1, digest, > + digest_len, true); > + kmem_cache_free(digest_list_item_cache, digest_list); > + return ERR_PTR(-ENOMEM); > + } > + > + digest_list->actions = actions; > + memcpy(digest_list->digest, digest, hash_digest_size[algo]); > + digest_list->algo = algo; > + digest_list->label = label; > + > + /* Add the digest of the digest list to the hash table. */ > + d = digest_add(digest, algo, COMPACT_DIGEST_LIST, digest_list, 0, 0); > + if (IS_ERR(d)) { > + kfree(digest_list->buf); > + kmem_cache_free(digest_list_item_cache, digest_list); > + } > + > + return d; > +} > + > +/** > + * digest_list_del - delete an existing digest list > + * @digest: digest of the digest list in binary form > + * @algo: digest algorithm > + * @actions: actions (measure/appraise) performed by IMA on the digest list > + * @digest_list: digest list to delete > + * > + * This function searches the digest of the digest list in the hash table for > + * the COMPACT_DIGEST_LIST type. If it is found, this function frees the buffer > + * and the digest list item allocated in digest_list_add(). > + * > + * This function will be executed only for digest lists that were previously > + * added. > + * > + * Proper locking must be provided by the caller. > + */ > +void digest_list_del(u8 *digest, enum hash_algo algo, u8 actions, > + struct digest_list_item *digest_list) > +{ > + /* Delete the digest item associated to the digest list. */ > + digest_del(digest, algo, COMPACT_DIGEST_LIST, digest_list, 0, 0); > + > + /* > + * Free the buffer and the digest list item allocated when the digest > + * list was added. > + */ > + kfree(digest_list->buf); > + kmem_cache_free(digest_list_item_cache, digest_list); > +} > + > +static int __init digest_list_cache_init(void) > +{ > + digest_list_item_cache = kmem_cache_create("digest_list_item_cache", > + sizeof(struct digest_list_item), > + 0, SLAB_PANIC, NULL); > + > + digest_list_item_ref_cache = kmem_cache_create( > + "digest_list_item_ref_cache", > + sizeof(struct digest_list_item_ref), 0, > + SLAB_PANIC, NULL); > + > + digest_item_cache = kmem_cache_create("digest_item_cache", > + sizeof(struct digest_item), 0, > + SLAB_PANIC, NULL); > + > + return 0; > +} > + > +late_initcall(digest_list_cache_init) Thanks, Mauro
> From: Mauro Carvalho Chehab [mailto:mchehab+huawei@kernel.org] > Sent: Wednesday, July 28, 2021 2:19 PM > Em Mon, 26 Jul 2021 18:36:52 +0200 > Roberto Sassu <roberto.sassu@huawei.com> escreveu: > > > Introduce the methods requires to manage the three objects defined. > > > > - digest_item methods: > > - digest_add() > > - digest_del() > > - __digest_lookup() > > - diglim_digest_get_info() > > > > - digest_list_item_ref methods: > > - digest_list_ref_add() > > - digest_list_ref_del() > > > > - digest_list_item methods: > > - digest_list_add() > > - digest_list_del() > > > > More information about these functions can be found in > > Documentation/security/diglim/implementation.rst. > > > > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com> > > --- > > .../security/diglim/implementation.rst | 9 + > > MAINTAINERS | 2 + > > include/linux/diglim.h | 28 + > > security/integrity/Kconfig | 1 + > > security/integrity/Makefile | 1 + > > security/integrity/diglim/Kconfig | 11 + > > security/integrity/diglim/Makefile | 8 + > > security/integrity/diglim/diglim.h | 20 +- > > security/integrity/diglim/methods.c | 499 ++++++++++++++++++ > > 9 files changed, 578 insertions(+), 1 deletion(-) > > create mode 100644 include/linux/diglim.h > > create mode 100644 security/integrity/diglim/Kconfig > > create mode 100644 security/integrity/diglim/Makefile > > create mode 100644 security/integrity/diglim/methods.c > > > > diff --git a/Documentation/security/diglim/implementation.rst > b/Documentation/security/diglim/implementation.rst > > index 6002049612a1..54af23b2f5f1 100644 > > --- a/Documentation/security/diglim/implementation.rst > > +++ b/Documentation/security/diglim/implementation.rst > > @@ -200,3 +200,12 @@ Similarly: > > the digest can be obtained by summing the address of the digest list buffer > > with ``digest_offset`` (except for the digest lists, where the digest is > > stored in the ``digest`` field of the ``digest_list_item`` structure). > > + > > + > > +Methods > > +------- > > + > > +This section introduces the methods requires to manage the three objects > > +defined. > > + > > +.. kernel-doc:: security/integrity/diglim/methods.c > > diff --git a/MAINTAINERS b/MAINTAINERS > > index f7592d41367d..9e085a36654a 100644 > > --- a/MAINTAINERS > > +++ b/MAINTAINERS > > @@ -5461,8 +5461,10 @@ F: > Documentation/security/diglim/architecture.rst > > F: Documentation/security/diglim/implementation.rst > > F: Documentation/security/diglim/index.rst > > F: Documentation/security/diglim/introduction.rst > > +F: include/linux/diglim.h > > F: include/uapi/linux/diglim.h > > F: security/integrity/diglim/diglim.h > > +F: security/integrity/diglim/methods.c > > > > DIOLAN U2C-12 I2C DRIVER > > M: Guenter Roeck <linux@roeck-us.net> > > diff --git a/include/linux/diglim.h b/include/linux/diglim.h > > new file mode 100644 > > index 000000000000..d4b4548a288b > > --- /dev/null > > +++ b/include/linux/diglim.h > > @@ -0,0 +1,28 @@ > > +/* SPDX-License-Identifier: GPL-2.0 */ > > +/* > > + * Copyright (C) 2017-2021 Huawei Technologies Duesseldorf GmbH > > + * > > + * Author: Roberto Sassu <roberto.sassu@huawei.com> > > + * > > + * DIGLIM functions available for use by kernel subsystems. > > + */ > > + > > +#ifndef __DIGLIM_H > > +#define __DIGLIM_H > > + > > +#include <crypto/hash_info.h> > > +#include <uapi/linux/diglim.h> > > + > > +#ifdef CONFIG_DIGLIM > > +extern int diglim_digest_get_info(u8 *digest, enum hash_algo algo, > > + enum compact_types type, u16 *modifiers, > > + u8 *actions); > > +#else > > +static inline int diglim_digest_get_info(u8 *digest, enum hash_algo algo, > > + enum compact_types type, > > + u16 *modifiers, u8 *actions) > > +{ > > + return -ENOENT; > > +} > > +#endif /*CONFIG_DIGLIM*/ > > +#endif /*__DIGLIM_H*/ > > diff --git a/security/integrity/Kconfig b/security/integrity/Kconfig > > index 71f0177e8716..8f94f4dcc052 100644 > > --- a/security/integrity/Kconfig > > +++ b/security/integrity/Kconfig > > @@ -98,5 +98,6 @@ config INTEGRITY_AUDIT > > > > source "security/integrity/ima/Kconfig" > > source "security/integrity/evm/Kconfig" > > +source "security/integrity/diglim/Kconfig" > > > > endif # if INTEGRITY > > diff --git a/security/integrity/Makefile b/security/integrity/Makefile > > index 7ee39d66cf16..d6166550a6b8 100644 > > --- a/security/integrity/Makefile > > +++ b/security/integrity/Makefile > > @@ -19,3 +19,4 @@ integrity-$(CONFIG_LOAD_PPC_KEYS) += > platform_certs/efi_parser.o \ > > platform_certs/keyring_handler.o > > obj-$(CONFIG_IMA) += ima/ > > obj-$(CONFIG_EVM) += evm/ > > +obj-$(CONFIG_DIGLIM) += diglim/ > > diff --git a/security/integrity/diglim/Kconfig > b/security/integrity/diglim/Kconfig > > new file mode 100644 > > index 000000000000..436a76a14337 > > --- /dev/null > > +++ b/security/integrity/diglim/Kconfig > > @@ -0,0 +1,11 @@ > > +# SPDX-License-Identifier: GPL-2.0-only > > +# Digest Lists Integrity Module (DIGLIM) > > +# > > +config DIGLIM > > + bool "Digest Lists Integrity Module (DIGLIM)" > > + select SECURITYFS > > + select CRYPTO > > + select CRYPTO_HASH_INFO > > + help > > + DIGLIM provides reference values for file content and metadata, > > + that can be used for measurement and appraisal with IMA. > > diff --git a/security/integrity/diglim/Makefile > b/security/integrity/diglim/Makefile > > new file mode 100644 > > index 000000000000..b761ed8cfb3e > > --- /dev/null > > +++ b/security/integrity/diglim/Makefile > > @@ -0,0 +1,8 @@ > > +# SPDX-License-Identifier: GPL-2.0 > > +# > > +# Makefile for building Digest Lists Integrity Module (DIGLIM). > > +# > > + > > +obj-$(CONFIG_DIGLIM) += diglim.o > > + > > +diglim-y := methods.o > > diff --git a/security/integrity/diglim/diglim.h > b/security/integrity/diglim/diglim.h > > index 578253d7e1d1..25851e7d4906 100644 > > --- a/security/integrity/diglim/diglim.h > > +++ b/security/integrity/diglim/diglim.h > > @@ -20,7 +20,7 @@ > > #include <linux/audit.h> > > #include <crypto/hash_info.h> > > #include <linux/hash_info.h> > > -#include <uapi/linux/diglim.h> > > +#include <linux/diglim.h> > > > > #define MAX_DIGEST_SIZE 64 > > #define HASH_BITS 10 > > @@ -81,6 +81,8 @@ static inline unsigned int hash_key(u8 *digest) > > return (digest[0] | digest[1] << 8) % DIGLIM_HTABLE_SIZE; > > } > > > > +extern struct h_table htable[COMPACT__LAST]; > > + > > it sounds somewhat risky to use just "htable" for a var declared > as external. Ok, adding diglim_ as prefix should be enough. > > static inline struct compact_list_hdr *get_hdr( > > struct digest_list_item *digest_list, > > loff_t hdr_offset) > > @@ -131,4 +133,20 @@ static inline u8 *get_digest_ref(struct > digest_list_item_ref *ref) > > > > return ref->digest_list->buf + ref->digest_offset; > > } > > + > > +struct digest_item *__digest_lookup(u8 *digest, enum hash_algo algo, > > + enum compact_types type, u16 *modifiers, > > + u8 *actions); > > +struct digest_item *digest_add(u8 *digest, enum hash_algo algo, > > + enum compact_types type, > > + struct digest_list_item *digest_list, > > + loff_t digest_offset, loff_t hdr_offset); > > +void digest_del(u8 *digest, enum hash_algo algo, enum compact_types > type, > > + struct digest_list_item *digest_list, loff_t digest_offset, > > + loff_t hdr_offset); > > +struct digest_item *digest_list_add(u8 *digest, enum hash_algo algo, > > + loff_t size, u8 *buf, u8 actions, > > + const char *label); > > +void digest_list_del(u8 *digest, enum hash_algo algo, u8 actions, > > + struct digest_list_item *digest_list); > > #endif /*__DIGLIM_INTERNAL_H*/ > > diff --git a/security/integrity/diglim/methods.c > b/security/integrity/diglim/methods.c > > new file mode 100644 > > index 000000000000..7ed61399cfe8 > > --- /dev/null > > +++ b/security/integrity/diglim/methods.c > > @@ -0,0 +1,499 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > +/* > > + * Copyright (C) 2005,2006,2007,2008 IBM Corporation > > + * Copyright (C) 2017-2021 Huawei Technologies Duesseldorf GmbH > > + * > > + * Author: Roberto Sassu <roberto.sassu@huawei.com> > > + * > > + * Functions to manage digest lists. > > + */ > > + > > +#include <linux/vmalloc.h> > > +#include <linux/module.h> > > +#include <linux/fault-inject.h> > > + > > +#include "diglim.h" > > +#include "../integrity.h" > > + > > +/* Define a cache for each object type. */ > > +static struct kmem_cache *digest_list_item_cache __read_mostly; > > +static struct kmem_cache *digest_list_item_ref_cache __read_mostly; > > +static struct kmem_cache *digest_item_cache __read_mostly; > > + > > +/* Define a hash table for each digest type. */ > > +struct h_table htable[COMPACT__LAST] = {{ > > + .queue[0 ... DIGLIM_HTABLE_SIZE - 1] = HLIST_HEAD_INIT > > +}}; > > > > + > > +#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS > > +static DECLARE_FAULT_ATTR(fail_diglim); > > + > > +static int __init fail_diglim_debugfs(void) > > +{ > > + struct dentry *dir = fault_create_debugfs_attr("fail_diglim", NULL, > > + &fail_diglim); > > + > > + return PTR_ERR_OR_ZERO(dir); > > +} > > + > > +static inline bool should_fail_diglim(void) > > +{ > > + return should_fail(&fail_diglim, 1); > > +} > > + > > +late_initcall(fail_diglim_debugfs); > > +#else > > +static inline bool should_fail_diglim(void) > > +{ > > + return false; > > +} > > +#endif > > > I guess this is a matter of personal preference, but, IMO, it is a lot better > to place the debugfs stuff on a separate source file, avoiding ugly #ifdefs > in the middle of the code. > > Ok, the current code is too small to deserve a separate file, but > if later patches would add more stuff, then I would opt to have this on > a separate file. Ok. Thanks Roberto HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Li Peng, Li Jian, Shi Yanli > > + > > +/** > > + * __digest_lookup - lookup digest and return associated modifiers and > actions > > + * @digest: digest to lookup > > + * @algo: digest algorithm > > + * @type: type of digest to lookup (e.g. file, metadata) > > + * @modifiers: modifiers (attributes) associated to the found digest > > + * @actions: actions performed by IMA on the digest list containing the > digest > > + * > > + * This function searches the given digest in the hash table depending on > the > > + * passed type and sets the modifiers and actions associated to the digest, if > > + * the pointers are not NULL. > > + * > > + * This function is not intended for external use, as the returned digest item > > + * could be freed at any time after it has been returned. > > + * diglim_digest_get_info() should be used instead by external callers, as it > > + * only returns the modifiers and the actions associated to the digest at the > > + * time the digest is searched. > > + * > > + * RCU protects both the hash table and the linked list of references to the > > + * digest lists containing the found digest. > > + * > > + * Return: a digest_item structure if the digest is found, NULL otherwise. > > + */ > > +struct digest_item *__digest_lookup(u8 *digest, enum hash_algo algo, > > + enum compact_types type, u16 *modifiers, > > + u8 *actions) > > +{ > > + struct digest_item *d = NULL; > > + struct digest_list_item_ref *ref; > > + int digest_len = hash_digest_size[algo]; > > + unsigned int key = hash_key(digest); > > + bool found = false; > > + > > + rcu_read_lock(); > > + hlist_for_each_entry_rcu(d, &htable[type].queue[key], hnext) { > > + list_for_each_entry_rcu(ref, &d->refs, list) { > > + if (get_algo_ref(ref) != algo || > > + memcmp(get_digest_ref(ref), digest, digest_len)) > > + break; > > + > > + found = true; > > + > > + /* There is no need to scan all digest list refs. */ > > + if (!modifiers || !actions) > > + break; > > + > > + /* > > + * The resulting modifiers and actions are the OR of > the > > + * modifiers and actions for each digest list. > > + */ > > + *modifiers |= get_hdr_ref(ref)->modifiers; > > + *actions |= ref->digest_list->actions; > > + } > > + > > + if (found) > > + break; > > + } > > + > > + rcu_read_unlock(); > > + return d; > > +} > > + > > +/** > > + * diglim_digest_get_info - lookup digest and return modifiers and actions > > + * @digest: digest to lookup > > + * @algo: digest algorithm > > + * @type: type of digest to lookup (e.g. file, metadata) > > + * @modifiers: modifiers (attributes) associated to the found digest > > + * @actions: actions performed by IMA on the digest lists containing the > digest > > + * > > + * This function searches the given digest in the hash table depending on > the > > + * passed type and sets the modifiers and actions associated to the digest, if > > + * the pointers are not NULL. > > + * > > + * This function is safe for external use, as it does not return pointers of > > + * objects that can be freed without the caller notices it. > > + * > > + * Return: 0 if the digest is found, -ENOENT otherwise. > > + */ > > +int diglim_digest_get_info(u8 *digest, enum hash_algo algo, > > + enum compact_types type, u16 *modifiers, u8 > *actions) > > +{ > > + struct digest_item *d; > > + > > + d = __digest_lookup(digest, algo, type, modifiers, actions); > > + if (!d) > > + return -ENOENT; > > + > > + return 0; > > +} > > + > > +/** > > + * digest_list_ref_add - add reference to a digest list > > + * @d: digest a new reference is added to > > + * @digest_list: digest list whose reference is being added > > + * @digest_offset: offset of the digest in the buffer of the digest list > > + * @hdr_offset: offset of the header within the digest list the digest refers > to > > + * > > + * This function adds a new reference to an existing digest list for a given > > + * digest. The reference is described by the digest_list_item_ref structure > and > > + * consists of a pointer of the digest list, the offset of the digest to the > > + * beginning of the digest list buffer and the offset of the header the digest > > + * refers to (each digest list might be composed of several digest blocks, > each > > + * prefixed by a header describing the attributes of those digests). > > + * > > + * Return: 0 if a new digest list reference was successfully added, a negative > > + * value otherwise. > > + */ > > +static int digest_list_ref_add(struct digest_item *d, > > + struct digest_list_item *digest_list, > > + loff_t digest_offset, loff_t hdr_offset) > > +{ > > + struct digest_list_item_ref *new_ref = NULL; > > + u8 *digest = get_digest(digest_list, digest_offset, hdr_offset); > > + enum hash_algo algo = get_algo(digest_list, digest_offset, hdr_offset); > > + int digest_len = hash_digest_size[algo]; > > + > > + /* Allocate a new reference. */ > > + if (!should_fail_diglim()) > > + new_ref = kmem_cache_alloc(digest_list_item_ref_cache, > > + GFP_KERNEL); > > + if (!new_ref) { > > + print_hex_dump(KERN_ERR, "digest list ref allocation failed: ", > > + DUMP_PREFIX_NONE, digest_len, 1, digest, > > + digest_len, true); > > + return -ENOMEM; > > + } > > + > > + /* Set the new reference. */ > > + new_ref->digest_list = digest_list; > > + /* Converting loff_t -> u32 is fine as long as the digest list < 4G. */ > > + new_ref->digest_offset = digest_offset; > > + new_ref->hdr_offset = hdr_offset; > > + > > + list_add_tail_rcu(&new_ref->list, &d->refs); > > + > > + print_hex_dump_debug("add digest list ref: ", DUMP_PREFIX_NONE, > > + digest_len, 1, digest, digest_len, true); > > + return 0; > > +} > > + > > +/** > > + * digest_list_ref_del - del reference to a digest list > > + * @d: digest a reference is deleted from > > + * @digest_list: digest list whose reference is being deleted > > + * @digest_offset: offset of the digest in the buffer of the digest list > > + * @hdr_offset: offset of the header within the digest list the digest refers > to > > + * > > + * This function searches the reference to an already loaded digest list in > the > > + * linked list of references stored for each digest item. If the reference is > > + * found (if not, it is a bug), the function deletes it from the linked list. > > + */ > > +static void digest_list_ref_del(struct digest_item *d, > > + struct digest_list_item *digest_list, > > + loff_t digest_offset, loff_t hdr_offset) > > +{ > > + struct digest_list_item_ref *ref; > > + u8 *digest = get_digest(digest_list, digest_offset, hdr_offset); > > + enum hash_algo algo = get_algo(digest_list, digest_offset, hdr_offset); > > + int digest_len = hash_digest_size[algo]; > > + > > + /* Search for a digest list reference. */ > > + list_for_each_entry(ref, &d->refs, list) > > + if (ref->digest_list == digest_list) > > + break; > > + > > + if (!ref) { > > + print_hex_dump(KERN_ERR, "digest list ref not found: ", > > + DUMP_PREFIX_NONE, digest_len, 1, digest, > > + digest_len, true); > > + return; > > + } > > + > > + list_del_rcu(&ref->list); > > + kmem_cache_free(digest_list_item_ref_cache, ref); > > + > > + print_hex_dump_debug("del digest list ref: ", DUMP_PREFIX_NONE, > > + digest_len, 1, digest, digest_len, true); > > +} > > + > > +/** > > + * digest_add - add a new digest > > + * @digest: digest in binary form > > + * @algo: digest algorithm > > + * @type: digest type > > + * @digest_list: digest list the new digest belongs to > > + * @digest_offset: offset of the digest in the buffer of the digest list > > + * @hdr_offset: offset of the header within the digest list the digest refers > to > > + * > > + * This function first searches if the digest is already in the hash table for > > + * the given type. The digest is searched by comparing the passed digest > and > > + * algorithm with the digest obtained from the first digest list reference > > + * (buffer + digest_offset), or from the digest field of a digest list item, > > + * for a digest list. > > + * > > + * If the digest exists, only a new reference is added (there might be > multiple > > + * references to the same digest list). > > + * > > + * If the digest is not found, a new digest item is allocated and a reference > to > > + * the passed digest list is added to that item. The digest item is finally > > + * added to the hash table for the given type. > > + * > > + * Proper locking must be provided by the caller. > > + * > > + * Return: a new or the found digest item on success, an error pointer > > + * otherwise. > > + */ > > +struct digest_item *digest_add(u8 *digest, enum hash_algo algo, > > + enum compact_types type, > > + struct digest_list_item *digest_list, > > + loff_t digest_offset, loff_t hdr_offset) > > +{ > > + int digest_len = hash_digest_size[algo]; > > + struct digest_item *d; > > + int ret; > > + > > + /* Search the digest. */ > > + d = __digest_lookup(digest, algo, type, NULL, NULL); > > + if (d) { > > + /* > > + * Add a new digest list reference to the existing digest item. > > + */ > > + ret = digest_list_ref_add(d, digest_list, digest_offset, > > + hdr_offset); > > + if (ret < 0) > > + return ERR_PTR(ret); > > + > > + print_hex_dump_debug("digest add duplicate: ", > DUMP_PREFIX_NONE, > > + digest_len, 1, digest, digest_len, true); > > + return d; > > + } > > + > > + /* Allocate a new digest item. */ > > + if (!should_fail_diglim()) > > + d = kmem_cache_alloc(digest_item_cache, GFP_KERNEL); > > + if (!d) { > > + print_hex_dump_debug("digest allocation failed: ", > > + DUMP_PREFIX_NONE, digest_len, 1, digest, > > + digest_len, true); > > + return ERR_PTR(-ENOMEM); > > + } > > + > > + INIT_LIST_HEAD(&d->refs); > > + > > + /* Add a new digest list reference to the new digest item. */ > > + ret = digest_list_ref_add(d, digest_list, digest_offset, hdr_offset); > > + if (ret < 0) { > > + kmem_cache_free(digest_item_cache, d); > > + return ERR_PTR(ret); > > + } > > + > > + /* Add the new digest item to the hash table for the given type. */ > > + hlist_add_head_rcu(&d->hnext, > &htable[type].queue[hash_key(digest)]); > > + htable[type].len++; > > + > > + print_hex_dump_debug("digest add: ", DUMP_PREFIX_NONE, > digest_len, 1, > > + digest, digest_len, true); > > + return d; > > +} > > + > > +/** > > + * digest_del - delete a digest with one reference, or just a reference > > + * @digest: digest in binary form > > + * @algo: digest algorithm > > + * @type: digest type > > + * @digest_list: digest list the digest belongs to > > + * @digest_offset: offset of the digest in the buffer of the digest list > > + * @hdr_offset: offset of the header within the digest list the digest refers > to > > + * > > + * This function is called when a digest list is being removed. The digest is > > + * first searched in the hash table for the given type. If it is found (if not, > > + * it is a bug, because digest lists can be deleted only if they were added > > + * previously), a reference of the passed digest list is deleted from the > linked > > + * list of references of the digest item. > > + * > > + * If the last reference was deleted, the digest item is also deleted and > > + * removed from the hash table. > > + * > > + * Proper locking must be provided by the caller. > > + */ > > +void digest_del(u8 *digest, enum hash_algo algo, enum compact_types > type, > > + struct digest_list_item *digest_list, loff_t digest_offset, > > + loff_t hdr_offset) > > +{ > > + struct digest_item *d; > > + int digest_len = hash_digest_size[algo]; > > + > > + /* Search the digest. */ > > + d = __digest_lookup(digest, algo, type, NULL, NULL); > > + if (!d) { > > + print_hex_dump(KERN_ERR, "digest not found: ", > DUMP_PREFIX_NONE, > > + digest_len, 1, digest, digest_len, true); > > + return; > > + } > > + > > + /* Delete a reference of the passed digest list. */ > > + digest_list_ref_del(d, digest_list, digest_offset, hdr_offset); > > + > > + print_hex_dump_debug(!list_empty(&d->refs) ? > > + "digest del duplicate: " : "digest del: ", > > + DUMP_PREFIX_NONE, digest_len, 1, digest, > > + digest_len, true); > > + > > + /* Return if there are still references. */ > > + if (!list_empty(&d->refs)) > > + return; > > + > > + /* > > + * Remove the digest item from the hash table and free it if there are > > + * no more references left. > > + */ > > + hlist_del_rcu(&d->hnext); > > + htable[type].len--; > > + kmem_cache_free(digest_item_cache, d); > > +} > > + > > +/** > > + * digest_list_add - add a new digest list > > + * @digest: digest of the digest list in binary form > > + * @algo: digest algorithm > > + * @size: digest list size > > + * @buf: digest list buffer > > + * @actions: actions (measure/appraise) performed by IMA on the digest > list > > + * @label: label to be used to identify the digest list > > + * > > + * This function allocates a new digest list item, which contains the buffer, > > + * size, actions performed by IMA and a label. Each digest list item is > > + * associated to a digest item representing the digest of the digest list. > > + * > > + * This function prevents the same digest list to be added multiple times by > > + * searching its digest in the hash table for the COMPACT_DIGEST_LIST > type. > > + * > > + * The passed buffer is copied in a new memory area, to avoid to reference > > + * memory that could be freed by the caller. > > + * > > + * If allocation of a new digest list and the associated buffer was successful, > > + * its digest is added to the hash table for the COMPACT_DIGEST_LIST type. > > + * > > + * Proper locking must be provided by the caller. > > + * > > + * Return: the digest item associated to the digest list item on success, an > > + * error pointer otherwise. > > + */ > > +struct digest_item *digest_list_add(u8 *digest, enum hash_algo algo, > > + loff_t size, u8 *buf, u8 actions, > > + const char *label) > > +{ > > + struct digest_item *d; > > + struct digest_list_item *digest_list = NULL; > > + int digest_len = hash_digest_size[algo]; > > + > > + /* Search the digest of the digest list. */ > > + d = __digest_lookup(digest, algo, COMPACT_DIGEST_LIST, NULL, > NULL); > > + if (d) { > > + print_hex_dump(KERN_ERR, "digest list already uploaded: ", > > + DUMP_PREFIX_NONE, digest_len, 1, digest, > > + digest_len, true); > > + return ERR_PTR(-EEXIST); > > + } > > + > > + /* Allocate a new digest list. */ > > + if (!should_fail_diglim()) > > + digest_list = kmem_cache_alloc(digest_list_item_cache, > > + GFP_KERNEL); > > + if (!digest_list) { > > + print_hex_dump(KERN_ERR, "digest list allocation failed: ", > > + DUMP_PREFIX_NONE, digest_len, 1, digest, > > + digest_len, true); > > + return ERR_PTR(-ENOMEM); > > + } > > + > > + digest_list->buf = NULL; > > + digest_list->size = size; > > + > > + if (!should_fail_diglim()) > > + digest_list->buf = kmemdup(buf, size, GFP_KERNEL); > > + if (!digest_list->buf) { > > + print_hex_dump(KERN_ERR, "digest list allocation failed: ", > > + DUMP_PREFIX_NONE, digest_len, 1, digest, > > + digest_len, true); > > + kmem_cache_free(digest_list_item_cache, digest_list); > > + return ERR_PTR(-ENOMEM); > > + } > > + > > + digest_list->actions = actions; > > + memcpy(digest_list->digest, digest, hash_digest_size[algo]); > > + digest_list->algo = algo; > > + digest_list->label = label; > > + > > + /* Add the digest of the digest list to the hash table. */ > > + d = digest_add(digest, algo, COMPACT_DIGEST_LIST, digest_list, 0, 0); > > + if (IS_ERR(d)) { > > + kfree(digest_list->buf); > > + kmem_cache_free(digest_list_item_cache, digest_list); > > + } > > + > > + return d; > > +} > > + > > +/** > > + * digest_list_del - delete an existing digest list > > + * @digest: digest of the digest list in binary form > > + * @algo: digest algorithm > > + * @actions: actions (measure/appraise) performed by IMA on the digest > list > > + * @digest_list: digest list to delete > > + * > > + * This function searches the digest of the digest list in the hash table for > > + * the COMPACT_DIGEST_LIST type. If it is found, this function frees the > buffer > > + * and the digest list item allocated in digest_list_add(). > > + * > > + * This function will be executed only for digest lists that were previously > > + * added. > > + * > > + * Proper locking must be provided by the caller. > > + */ > > +void digest_list_del(u8 *digest, enum hash_algo algo, u8 actions, > > + struct digest_list_item *digest_list) > > +{ > > + /* Delete the digest item associated to the digest list. */ > > + digest_del(digest, algo, COMPACT_DIGEST_LIST, digest_list, 0, 0); > > + > > + /* > > + * Free the buffer and the digest list item allocated when the digest > > + * list was added. > > + */ > > + kfree(digest_list->buf); > > + kmem_cache_free(digest_list_item_cache, digest_list); > > +} > > + > > +static int __init digest_list_cache_init(void) > > +{ > > + digest_list_item_cache = > kmem_cache_create("digest_list_item_cache", > > + sizeof(struct digest_list_item), > > + 0, SLAB_PANIC, NULL); > > + > > + digest_list_item_ref_cache = kmem_cache_create( > > + "digest_list_item_ref_cache", > > + sizeof(struct digest_list_item_ref), 0, > > + SLAB_PANIC, NULL); > > + > > + digest_item_cache = kmem_cache_create("digest_item_cache", > > + sizeof(struct digest_item), 0, > > + SLAB_PANIC, NULL); > > + > > + return 0; > > +} > > + > > +late_initcall(digest_list_cache_init) > > > > Thanks, > Mauro
Em Mon, 26 Jul 2021 18:36:53 +0200 Roberto Sassu <roberto.sassu@huawei.com> escreveu: > Introduce the necessary functions to parse a digest list and to execute the > requested operation. > > The main function is digest_list_parse(), which coordinates the various > steps required to add or delete a digest list, and has the logic to roll > back when one of the steps fails. > > A more detailed description about the steps can be found in > Documentation/security/diglim/implementation.rst LGTM. > > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com> > --- > .../security/diglim/implementation.rst | 35 +++ > MAINTAINERS | 1 + > security/integrity/diglim/Makefile | 2 +- > security/integrity/diglim/diglim.h | 3 + > security/integrity/diglim/parser.c | 274 ++++++++++++++++++ > 5 files changed, 314 insertions(+), 1 deletion(-) > create mode 100644 security/integrity/diglim/parser.c > > diff --git a/Documentation/security/diglim/implementation.rst b/Documentation/security/diglim/implementation.rst > index 54af23b2f5f1..9d679567a037 100644 > --- a/Documentation/security/diglim/implementation.rst > +++ b/Documentation/security/diglim/implementation.rst > @@ -209,3 +209,38 @@ This section introduces the methods requires to manage the three objects > defined. > > .. kernel-doc:: security/integrity/diglim/methods.c > + > + > +Parser > +------ > + > +This section introduces the necessary functions to parse a digest list and > +to execute the requested operation. > + > +.. kernel-doc:: security/integrity/diglim/parser.c > + > +The main function is digest_list_parse(), which coordinates the various > +steps required to add or delete a digest list, and has the logic to roll > +back when one of the steps fails. > + > +#. Calls digest_list_validate() to validate the passed buffer containing > + the digest list to ensure that the format is correct. > + > +#. Calls get_digest_list() to create a new digest_list_item for the add > + operation, or to retrieve the existing one for the delete operation. > + get_digest_list() refuses to add digest lists that were previously > + added and to delete digest lists that weren't previously added. Also, > + get_digest_list() refuses to delete digest lists if there are actions > + done at addition time that are not currently being performed (it would > + guarantee that also deletion is notified to remote verifiers). > + > +#. Calls _digest_list_parse() which takes the created/retrieved > + struct digest_list_item and adds or delete the digests included in the > + digest list. > + > +#. If an error occurred, performs a rollback to the previous state, by > + calling _digest_list_parse() with the opposite operation and the buffer > + size at the time the error occurred. > + > +#. digest_list_parse() deletes the struct digest_list_item on unsuccessful > + add or successful delete. > diff --git a/MAINTAINERS b/MAINTAINERS > index 9e085a36654a..77c3613c600a 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -5465,6 +5465,7 @@ F: include/linux/diglim.h > F: include/uapi/linux/diglim.h > F: security/integrity/diglim/diglim.h > F: security/integrity/diglim/methods.c > +F: security/integrity/diglim/parser.c > > DIOLAN U2C-12 I2C DRIVER > M: Guenter Roeck <linux@roeck-us.net> > diff --git a/security/integrity/diglim/Makefile b/security/integrity/diglim/Makefile > index b761ed8cfb3e..34e4e154fff3 100644 > --- a/security/integrity/diglim/Makefile > +++ b/security/integrity/diglim/Makefile > @@ -5,4 +5,4 @@ > > obj-$(CONFIG_DIGLIM) += diglim.o > > -diglim-y := methods.o > +diglim-y := methods.o parser.o > diff --git a/security/integrity/diglim/diglim.h b/security/integrity/diglim/diglim.h > index 25851e7d4906..3adc218a0325 100644 > --- a/security/integrity/diglim/diglim.h > +++ b/security/integrity/diglim/diglim.h > @@ -149,4 +149,7 @@ struct digest_item *digest_list_add(u8 *digest, enum hash_algo algo, > const char *label); > void digest_list_del(u8 *digest, enum hash_algo algo, u8 actions, > struct digest_list_item *digest_list); > + > +int digest_list_parse(loff_t size, void *buf, enum ops op, u8 actions, > + u8 *digest, enum hash_algo algo, const char *label); > #endif /*__DIGLIM_INTERNAL_H*/ > diff --git a/security/integrity/diglim/parser.c b/security/integrity/diglim/parser.c > new file mode 100644 > index 000000000000..89a48945b460 > --- /dev/null > +++ b/security/integrity/diglim/parser.c > @@ -0,0 +1,274 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * Copyright (C) 2005,2006,2007,2008 IBM Corporation > + * Copyright (C) 2017-2021 Huawei Technologies Duesseldorf GmbH > + * > + * Author: Roberto Sassu <roberto.sassu@huawei.com> > + * > + * Functions to parse digest lists. > + */ > + > +#include <linux/vmalloc.h> > +#include <linux/module.h> > + > +#include "diglim.h" > +#include "../integrity.h" > + > +/** > + * digest_list_validate - validate format of digest list > + * @size: buffer size > + * @buf: buffer containing the digest list > + * > + * This function validates the format of the passed digest list. > + * > + * Return: 0 if the digest list was successfully validated, -EINVAL otherwise. > + */ > +static int digest_list_validate(loff_t size, void *buf) > +{ > + void *bufp = buf, *bufendp = buf + size; > + struct compact_list_hdr *hdr; > + size_t digest_len; > + > + while (bufp < bufendp) { > + if (bufp + sizeof(*hdr) > bufendp) { > + pr_err("invalid data\n"); > + return -EINVAL; > + } > + > + hdr = bufp; > + > + if (hdr->version != 1) { > + pr_err("unsupported version\n"); > + return -EINVAL; > + } > + > + if (hdr->_reserved != 0) { > + pr_err("unexpected value for _reserved field\n"); > + return -EINVAL; > + } > + > + hdr->type = le16_to_cpu(hdr->type); > + hdr->modifiers = le16_to_cpu(hdr->modifiers); > + hdr->algo = le16_to_cpu(hdr->algo); > + hdr->count = le32_to_cpu(hdr->count); > + hdr->datalen = le32_to_cpu(hdr->datalen); > + > + if (hdr->algo >= HASH_ALGO__LAST) { > + pr_err("invalid hash algorithm\n"); > + return -EINVAL; > + } > + > + digest_len = hash_digest_size[hdr->algo]; > + > + if (hdr->type >= COMPACT__LAST || > + hdr->type == COMPACT_DIGEST_LIST) { > + pr_err("invalid type %d\n", hdr->type); > + return -EINVAL; > + } > + > + bufp += sizeof(*hdr); > + > + if (hdr->datalen != hdr->count * digest_len || > + bufp + hdr->datalen > bufendp) { > + pr_err("invalid data\n"); > + return -EINVAL; > + } > + > + bufp += hdr->count * digest_len; > + } > + > + return 0; > +} > + > +/** > + * _digest_list_parse - parse digest list and add/delete digests > + * @size: buffer size > + * @buf: buffer containing the digest list > + * @op: operation to be performed > + * @digest_list: digest list digests being added/deleted belong to > + * > + * This function parses the digest list and adds or delete the digests in the > + * found digest blocks. > + * > + * Return: the buffer size if all digests were successfully added or deleted, > + * the size of the already parsed buffer on error. > + */ > +static int _digest_list_parse(loff_t size, void *buf, enum ops op, > + struct digest_list_item *digest_list) > +{ > + void *bufp = buf, *bufendp = buf + size; > + struct compact_list_hdr *hdr; > + struct digest_item *d = ERR_PTR(-EINVAL); > + size_t digest_len; > + int i; > + > + while (bufp < bufendp) { > + if (bufp + sizeof(*hdr) > bufendp) > + break; > + > + hdr = bufp; > + bufp += sizeof(*hdr); > + > + digest_len = hash_digest_size[hdr->algo]; > + > + for (i = 0; i < hdr->count && bufp + digest_len <= bufendp; > + i++, bufp += digest_len) { > + switch (op) { > + case DIGEST_LIST_ADD: > + d = digest_add(bufp, hdr->algo, hdr->type, > + digest_list, bufp - buf, > + (void *)hdr - buf); > + if (IS_ERR(d)) { > + pr_err( > + "failed to add a digest from %s\n", > + digest_list->label); > + goto out; > + } > + > + break; > + case DIGEST_LIST_DEL: > + digest_del(bufp, hdr->algo, hdr->type, > + digest_list, bufp - buf, > + (void *)hdr - buf); > + break; > + default: > + break; > + } > + } > + } > +out: > + return bufp - buf; > +} > + > +/** > + * get_digest_list - get the digest list extracted digests will be associated to > + * @size: buffer size > + * @buf: buffer containing the digest list > + * @op: digest list operation > + * @actions: actions performed on the digest list being processed > + * @digest: digest of the digest list > + * @algo: digest algorithm > + * @label: label to identify the digest list (e.g. file name) > + * > + * This function retrieves the digest list item for the passed digest and > + * algorithm. If it is not found at addition time, this function creates a new > + * one. > + * > + * This function prevents the imbalance of digests (references left after > + * delete) by ensuring that only digest lists that were previously added can be > + * deleted. > + * > + * This function also ensures that the actions done at the time of addition are > + * also performed at the time of deletion (it would guarantee that also deletion > + * is notified to remote verifiers). > + * > + * Return: the retrieved/created digest list item on success, an error pointer > + * otherwise. > + */ > +static struct digest_list_item *get_digest_list(loff_t size, void *buf, > + enum ops op, u8 actions, > + u8 *digest, enum hash_algo algo, > + const char *label) > +{ > + struct digest_item *d; > + struct digest_list_item *digest_list; > + int digest_len = hash_digest_size[algo]; > + > + switch (op) { > + case DIGEST_LIST_ADD: > + /* Add digest list to be associated to each digest. */ > + d = digest_list_add(digest, algo, size, buf, actions, label); > + if (IS_ERR(d)) > + return (void *)d; > + > + digest_list = list_first_entry(&d->refs, > + struct digest_list_item_ref, list)->digest_list; > + break; > + case DIGEST_LIST_DEL: > + /* Lookup digest list to delete the references. */ > + d = __digest_lookup(digest, algo, COMPACT_DIGEST_LIST, NULL, > + NULL); > + if (!d) { > + print_hex_dump(KERN_ERR, > + "digest list digest not found: ", > + DUMP_PREFIX_NONE, digest_len, 1, digest, > + digest_len, true); > + return ERR_PTR(-ENOENT); > + } > + > + digest_list = list_first_entry(&d->refs, > + struct digest_list_item_ref, list)->digest_list; > + > + /* > + * Reject deletion if there are actions done at addition time > + * that are currently not being performed. > + */ > + if ((digest_list->actions & actions) != digest_list->actions) { > + pr_err("missing actions, add: %d, del: %d\n", > + digest_list->actions, actions); > + return ERR_PTR(-EPERM); > + } > + > + break; > + default: > + return ERR_PTR(-EINVAL); > + } > + > + return digest_list; > +} > + > +/** > + * digest_list_parse - parse a digest list > + * @size: buffer size > + * @buf: buffer containing the digest list > + * @op: digest list operation > + * @actions: actions performed on the digest list being processed > + * @digest: digest of the digest list > + * @algo: digest algorithm > + * @label: label to identify the digest list (e.g. file name) > + * > + * This function parses the passed digest list and executed the requested > + * operation. If the operation cannot be successfully executed, this function > + * performs a rollback to the previous state. > + * > + * Return: the buffer size on success, a negative value otherwise. > + */ > +int digest_list_parse(loff_t size, void *buf, enum ops op, u8 actions, > + u8 *digest, enum hash_algo algo, const char *label) > +{ > + struct digest_list_item *digest_list; > + enum ops rollback_op = (op == DIGEST_LIST_ADD) ? > + DIGEST_LIST_DEL : DIGEST_LIST_ADD; > + int ret, rollback_size; > + > + ret = digest_list_validate(size, buf); > + if (ret < 0) > + return ret; > + > + digest_list = get_digest_list(size, buf, op, actions, digest, algo, > + label); > + if (IS_ERR(digest_list)) > + return PTR_ERR(digest_list); > + > + ret = _digest_list_parse(size, buf, op, digest_list); > + if (ret < 0) > + goto out; > + > + if (ret != size) { > + rollback_size = ret; > + > + ret = _digest_list_parse(rollback_size, buf, rollback_op, > + digest_list); > + if (ret != rollback_size) > + pr_err("rollback failed\n"); > + > + ret = -EINVAL; > + } > +out: > + /* Delete digest list on unsuccessful add or successful delete. */ > + if ((op == DIGEST_LIST_ADD && ret < 0) || > + (op == DIGEST_LIST_DEL && ret == size)) > + digest_list_del(digest, algo, actions, digest_list); > + > + return ret; > +}
Em Mon, 26 Jul 2021 18:36:59 +0200 Roberto Sassu <roberto.sassu@huawei.com> escreveu: > Add more information about remote attestation with IMA and DIGLIM in > Documentation/security/diglim/remote_attestation.rst. > > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com> > --- > Documentation/security/diglim/index.rst | 1 + > .../security/diglim/remote_attestation.rst | 87 +++++++++++++++++++ > MAINTAINERS | 1 + > 3 files changed, 89 insertions(+) > create mode 100644 Documentation/security/diglim/remote_attestation.rst > > diff --git a/Documentation/security/diglim/index.rst b/Documentation/security/diglim/index.rst > index 4771134c2f0d..0f28c5ad71c0 100644 > --- a/Documentation/security/diglim/index.rst > +++ b/Documentation/security/diglim/index.rst > @@ -10,3 +10,4 @@ Digest Lists Integrity Module (DIGLIM) > introduction > architecture > implementation > + remote_attestation > diff --git a/Documentation/security/diglim/remote_attestation.rst b/Documentation/security/diglim/remote_attestation.rst > new file mode 100644 > index 000000000000..83fd7581c460 > --- /dev/null > +++ b/Documentation/security/diglim/remote_attestation.rst > @@ -0,0 +1,87 @@ > +.. SPDX-License-Identifier: GPL-2.0 > + > +Remote Attestation > +================== > + > +When a digest list is added or deleted through the ``digest_list_add`` or > +``digest_list_del`` interfaces, its buffer is sent to the IMA function > +``ima_measure_critical_data()``. The primary reason for it is to calculate > +the buffer digest, so that the digest list itself is searchable in the hash > +table. > + > +``ima_measure_critical_data()`` can be also used to create a new > +measurement entry each time this function is called, if there is an > +appropriate rule in the IMA policy. Given that this function is called > +during an addition or deletion of a digest list, a remote verifier can > +infer from the measurement list precise information about what has been > +uploaded to the kernel. > + > +To enable this functionality, the following rule must be added to the IMA > +policy: > + > +:: As commented on other patches at this series, you can merge :: at the previous text line, e. g.: policy:: does the same as: policy: :: but it is nicer for text-only readers, IMO. > + > + measure func=CRITICAL_DATA label=diglim > + > + > +When a file is uploaded, the workflow and the resulting IMA measurement > +list are: > + > +.. code-block:: bash > + > + # echo $PWD/0-file_list-compact-cat > /sys/kernel/security/integrity/diglim/digest_list_add > + # echo $PWD/0-file_list-compact-cat > /sys/kernel/security/integrity/diglim/digest_list_del > + # cat /sys/kernel/security/integrity/ima/ascii_runtime_measurements > + ... > + 10 <template digest> ima-buf sha256:<buffer digest> add_file_0-file_list-compact-cat <buffer> > + 10 <template digest> ima-buf sha256:<buffer digest> del_file_0-file_list-compact-cat <buffer> > + > +When a buffer is uploaded, the workflow and the resulting IMA measurement > +list are: > + > +.. code-block:: bash > + > + # echo 0-file_list-compact-cat > /sys/kernel/security/integrity/diglim/digest_label > + # cat 0-file_list-compact-cat > /sys/kernel/security/integrity/diglim/digest_list_add > + # echo 0-file_list-compact-cat > /sys/kernel/security/integrity/diglim/digest_label > + # cat 0-file_list-compact-cat > /sys/kernel/security/integrity/diglim/digest_list_del > + # cat /sys/kernel/security/integrity/ima/ascii_runtime_measurements > + ... > + 10 <template digest> ima-buf sha256:<buffer digest> add_buffer_0-file_list-compact-cat <buffer> > + 10 <template digest> ima-buf sha256:<buffer digest> del_buffer_0-file_list-compact-cat <buffer> > + > +In the second case, the digest list label must be set explicitly, as the > +kernel cannot determine it by itself (in the first case it is derived from > +the name of the file uploaded). > + > +The confirmation that the digest list has been processed by IMA can be > +obtained by reading the ASCII representation of the digest list: > + > +.. code-block:: bash > + > + # cat /sys/kernel/security/integrity/diglim/digest_lists_loaded/sha256-<digest list digest>-0-file_list-compact-cat.ascii > + actions: 1, version: 1, algo: sha256, type: 2, modifiers: 1, count: 1, datalen: 32 > + 87e5bd81850e11eeec2d3bb696b626b2a7f45673241cbbd64769c83580432869 > + > +In this output, ``actions`` is set to 1 (``COMPACT_ACTION_IMA_MEASURED`` > +bit set). > + > + > +DIGLIM guarantees that the information reported in the IMA measurement list > +is complete. If digest list loading is not recorded, digest query results > +are ignored by IMA. If the addition was recorded, deletion can be performed > +only if also the deletion is recorded. This can be seen in the following > +sequence of commands: > + > +.. code-block:: bash > + > + # echo 0-file_list-compact-cat > /sys/kernel/security/integrity/diglim/digest_label > + # cat 0-file_list-compact-cat > /sys/kernel/security/integrity/diglim/digest_list_add > + # echo 0-file_list-compact-cat > /sys/kernel/security/integrity/diglim/digest_label > + # /tmp/cat 0-file_list-compact-cat > /sys/kernel/security/integrity/diglim/digest_list_del > + diglim: actions mismatch, add: 1, del: 0 > + diglim: unable to upload generated digest list > + /tmp/cat: write error: Invalid argument > + > +Digest list measurement is avoided with the execution of ``/tmp/cat``, for > +which a dont_measure rule was previously added in the IMA policy. > diff --git a/MAINTAINERS b/MAINTAINERS > index 0672128fae7f..a7c502685109 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -5461,6 +5461,7 @@ F: Documentation/security/diglim/architecture.rst > F: Documentation/security/diglim/implementation.rst > F: Documentation/security/diglim/index.rst > F: Documentation/security/diglim/introduction.rst > +F: Documentation/security/diglim/remote_attestation.rst > F: include/linux/diglim.h > F: include/uapi/linux/diglim.h > F: security/integrity/diglim/diglim.h
> From: Mauro Carvalho Chehab [mailto:mchehab+huawei@kernel.org] > Sent: Wednesday, July 28, 2021 2:47 PM > Em Mon, 26 Jul 2021 18:36:59 +0200 > Roberto Sassu <roberto.sassu@huawei.com> escreveu: > > > Add more information about remote attestation with IMA and DIGLIM in > > Documentation/security/diglim/remote_attestation.rst. > > > > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com> > > --- > > Documentation/security/diglim/index.rst | 1 + > > .../security/diglim/remote_attestation.rst | 87 +++++++++++++++++++ > > MAINTAINERS | 1 + > > 3 files changed, 89 insertions(+) > > create mode 100644 Documentation/security/diglim/remote_attestation.rst > > > > diff --git a/Documentation/security/diglim/index.rst > b/Documentation/security/diglim/index.rst > > index 4771134c2f0d..0f28c5ad71c0 100644 > > --- a/Documentation/security/diglim/index.rst > > +++ b/Documentation/security/diglim/index.rst > > @@ -10,3 +10,4 @@ Digest Lists Integrity Module (DIGLIM) > > introduction > > architecture > > implementation > > + remote_attestation > > diff --git a/Documentation/security/diglim/remote_attestation.rst > b/Documentation/security/diglim/remote_attestation.rst > > new file mode 100644 > > index 000000000000..83fd7581c460 > > --- /dev/null > > +++ b/Documentation/security/diglim/remote_attestation.rst > > @@ -0,0 +1,87 @@ > > +.. SPDX-License-Identifier: GPL-2.0 > > + > > +Remote Attestation > > +================== > > + > > +When a digest list is added or deleted through the ``digest_list_add`` or > > +``digest_list_del`` interfaces, its buffer is sent to the IMA function > > +``ima_measure_critical_data()``. The primary reason for it is to calculate > > +the buffer digest, so that the digest list itself is searchable in the hash > > +table. > > + > > +``ima_measure_critical_data()`` can be also used to create a new > > +measurement entry each time this function is called, if there is an > > +appropriate rule in the IMA policy. Given that this function is called > > +during an addition or deletion of a digest list, a remote verifier can > > +infer from the measurement list precise information about what has been > > +uploaded to the kernel. > > + > > +To enable this functionality, the following rule must be added to the IMA > > +policy: > > + > > +:: > > As commented on other patches at this series, you can merge :: at the > previous text line, e. g.: > > policy:: > > does the same as: > > policy: > > :: > > but it is nicer for text-only readers, IMO. Ok, will change in the next version of the patch set. Thanks Roberto HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Li Peng, Li Jian, Shi Yanli > > + > > + measure func=CRITICAL_DATA label=diglim > > + > > + > > +When a file is uploaded, the workflow and the resulting IMA measurement > > +list are: > > + > > +.. code-block:: bash > > + > > + # echo $PWD/0-file_list-compact-cat > > /sys/kernel/security/integrity/diglim/digest_list_add > > + # echo $PWD/0-file_list-compact-cat > > /sys/kernel/security/integrity/diglim/digest_list_del > > + # cat /sys/kernel/security/integrity/ima/ascii_runtime_measurements > > + ... > > + 10 <template digest> ima-buf sha256:<buffer digest> add_file_0-file_list- > compact-cat <buffer> > > + 10 <template digest> ima-buf sha256:<buffer digest> del_file_0-file_list- > compact-cat <buffer> > > + > > +When a buffer is uploaded, the workflow and the resulting IMA > measurement > > +list are: > > + > > +.. code-block:: bash > > + > > + # echo 0-file_list-compact-cat > > /sys/kernel/security/integrity/diglim/digest_label > > + # cat 0-file_list-compact-cat > > /sys/kernel/security/integrity/diglim/digest_list_add > > + # echo 0-file_list-compact-cat > > /sys/kernel/security/integrity/diglim/digest_label > > + # cat 0-file_list-compact-cat > > /sys/kernel/security/integrity/diglim/digest_list_del > > + # cat /sys/kernel/security/integrity/ima/ascii_runtime_measurements > > + ... > > + 10 <template digest> ima-buf sha256:<buffer digest> add_buffer_0- > file_list-compact-cat <buffer> > > + 10 <template digest> ima-buf sha256:<buffer digest> del_buffer_0-file_list- > compact-cat <buffer> > > + > > +In the second case, the digest list label must be set explicitly, as the > > +kernel cannot determine it by itself (in the first case it is derived from > > +the name of the file uploaded). > > + > > +The confirmation that the digest list has been processed by IMA can be > > +obtained by reading the ASCII representation of the digest list: > > + > > +.. code-block:: bash > > + > > + # cat /sys/kernel/security/integrity/diglim/digest_lists_loaded/sha256- > <digest list digest>-0-file_list-compact-cat.ascii > > + actions: 1, version: 1, algo: sha256, type: 2, modifiers: 1, count: 1, datalen: > 32 > > + > 87e5bd81850e11eeec2d3bb696b626b2a7f45673241cbbd64769c83580432869 > > + > > +In this output, ``actions`` is set to 1 > (``COMPACT_ACTION_IMA_MEASURED`` > > +bit set). > > + > > + > > +DIGLIM guarantees that the information reported in the IMA measurement > list > > +is complete. If digest list loading is not recorded, digest query results > > +are ignored by IMA. If the addition was recorded, deletion can be > performed > > +only if also the deletion is recorded. This can be seen in the following > > +sequence of commands: > > + > > +.. code-block:: bash > > + > > + # echo 0-file_list-compact-cat > > /sys/kernel/security/integrity/diglim/digest_label > > + # cat 0-file_list-compact-cat > > /sys/kernel/security/integrity/diglim/digest_list_add > > + # echo 0-file_list-compact-cat > > /sys/kernel/security/integrity/diglim/digest_label > > + # /tmp/cat 0-file_list-compact-cat > > /sys/kernel/security/integrity/diglim/digest_list_del > > + diglim: actions mismatch, add: 1, del: 0 > > + diglim: unable to upload generated digest list > > + /tmp/cat: write error: Invalid argument > > + > > +Digest list measurement is avoided with the execution of ``/tmp/cat``, for > > +which a dont_measure rule was previously added in the IMA policy. > > diff --git a/MAINTAINERS b/MAINTAINERS > > index 0672128fae7f..a7c502685109 100644 > > --- a/MAINTAINERS > > +++ b/MAINTAINERS > > @@ -5461,6 +5461,7 @@ F: > Documentation/security/diglim/architecture.rst > > F: Documentation/security/diglim/implementation.rst > > F: Documentation/security/diglim/index.rst > > F: Documentation/security/diglim/introduction.rst > > +F: Documentation/security/diglim/remote_attestation.rst > > F: include/linux/diglim.h > > F: include/uapi/linux/diglim.h > > F: security/integrity/diglim/diglim.h
This patch set depends on: - https://lore.kernel.org/linux-integrity/20210723085304.1760138-1-roberto.sassu@huawei.com/ - https://lore.kernel.org/linux-integrity/20210705115650.3373599-1-roberto.sassu@huawei.com/ I still kept pointer math to optimize the size of the digest_list_item_ref structure. Replacing offsets with pointers would cause the size of the structure to double. I could do this in the next version of the patch set if the size change is acceptable. Digest Lists Integrity Module (DIGLIM) is a new component added to the integrity subsystem in the kernel, primarily aiming to aid Integrity Measurement Architecture (IMA) in the process of checking the integrity of file content and metadata. It accomplishes this task by storing reference values coming from software vendors and by reporting whether or not the digest of file content or metadata calculated by IMA (or EVM) is found among those values. In this way, IMA can decide, depending on the result of a query, if a measurement should be taken or access to the file should be granted. The Security Assumptions section explains more in detail why this component has been placed in the kernel. The main benefits of using IMA in conjunction with DIGLIM are the ability to implement advanced remote attestation schemes based on the usage of a TPM key for establishing a TLS secure channel [1][2], and to reduce the burden on Linux distribution vendors to extend secure boot at OS level to applications. DIGLIM does not have the complexity of feature-rich databases. In fact, its main functionality comes from the hash table primitives already in the kernel. It does not have an ad-hoc storage module, it just indexes data in a fixed format (digest lists, a set of concatenated digests preceded by a header), copied to kernel memory as they are. Lastly, it does not support database-oriented languages such as SQL, but only accepts a digest and its algorithm as a query. The only digest list format supported by DIGLIM is called compact. However, Linux distribution vendors don't have to generate new digest lists in this format for the packages they release, as already available information, such as RPM headers and DEB package metadata, can be already used as a source for reference values (they already include file digests), with a user space parser taking care of the conversion to the compact format. Although one might perceive that storing file or metadata digests for a Linux distribution would significantly increase the memory usage, this does not seem to be the case. As an anticipation of the evaluation done in the Preliminary Performance Evaluation section, protecting binaries and shared libraries of a minimal Fedora 33 installation requires 208K of memory for the digest lists plus 556K for indexing. In exchange for a slightly increased memory usage, DIGLIM improves the performance of the integrity subsystem. In the considered scenario, IMA measurement and appraisal with digest lists requires respectively less than one quarter and less than half the time, compared to the current solution. DIGLIM also keeps track of whether digest lists have been processed in some way (e.g. measured or appraised by IMA). This is important for example for remote attestation, so that remote verifiers understand what has been uploaded to the kernel. DIGLIM behaves like a transactional database, i.e. it has the ability to roll back to the beginning of the transaction if an error occurred during the addition of a digest list (the deletion operation always succeeds). This capability has been tested with an ad-hoc fault injection mechanism capable of simulating failures during the operations. Finally, DIGLIM exposes to user space, through securityfs, the digest lists currently loaded, the number of digests added, a query interface and an interface to set digest list labels. [1] LSS EU 2019 - slides: https://static.sched.com/hosted_files/lsseu2019/bd/secure_attested_communication_channels_lss_eu_2019.pdf - video: https://youtu.be/mffdQgkvDNY [2] FutureTPM EU project, final review meeting demo - slides: https://futuretpm.eu/images/07-3-FutureTPM-Final-Review-Slides-WP6-Device-Management-Use-Case-HWDU.pdf - video: https://vimeo.com/528251864/4c1d55abcd Binary Integrity Integrity is a fundamental security property in information systems. Integrity could be described as the condition in which a generic component is just after it has been released by the entity that created it. One way to check whether a component is in this condition (called binary integrity) is to calculate its digest and to compare it with a reference value (i.e. the digest calculated in controlled conditions, when the component is released). IMA, a software part of the integrity subsystem, can perform such evaluation and execute different actions: - store the digest in an integrity-protected measurement list, so that it can be sent to a remote verifier for analysis; - compare the calculated digest with a reference value (usually protected with a signature) and deny operations if the file is found corrupted; - store the digest in the system log. Contribution DIGLIM further enhances the capabilities offered by IMA-based solutions and, at the same time, makes them more practical to adopt by reusing existing sources as reference values for integrity decisions. Possible sources for digest lists are: - RPM headers; - Debian repository metadata. Benefits for IMA Measurement One of the issues that arises when files are measured by the OS is that, due to parallel execution, the order in which file accesses happen cannot be predicted. Since the TPM Platform Configuration Register (PCR) extend operation, executed after each file measurement, cryptographically binds the current measurement to the previous ones, the PCR value at the end of a workload cannot be predicted too. Thus, even if the usage of a TPM key, bound to a PCR value, should be allowed when only good files were accessed, the TPM could unexpectedly deny an operation on that key if files accesses did not happen as stated by the key policy (which allows only one of the possible sequences). DIGLIM solves this issue by making the PCR value stable over the time and not dependent on file accesses. The following figure depicts the current and the new approaches: IMA measurement list (current) entry# 1st boot 2nd boot 3rd boot +----+---------------+ +----+---------------+ +----+---------------+ 1: | 10 | file1 measur. | | 10 | file3 measur. | | 10 | file2 measur. | +----+---------------+ +----+---------------+ +----+---------------+ 2: | 10 | file2 measur. | | 10 | file2 measur. | | 10 | file3 measur. | +----+---------------+ +----+---------------+ +----+---------------+ 3: | 10 | file3 measur. | | 10 | file1 measur. | | 10 | file4 measur. | +----+---------------+ +----+---------------+ +----+---------------+ PCR: Extend != Extend != Extend file1, file2, file3 file3, file2, file1 file2, file3, file4 PCR Extend definition: PCR(new value) = Hash(Hash(meas. entry), PCR(previous value)) A new entry in the measurement list is created by IMA for each file access. Assuming that file1, file2 and file3 are files provided by the software vendor, file4 is an unknown file, the first two PCR values above represent a good system state, the third a bad system state. The PCR values are the result of the PCR extend operation performed for each measurement entry with the digest of the measurement entry as an input. IMA measurement list (with DIGLIM) dlist +--------------+ | header | +--------------+ | file1 digest | | file2 digest | | file3 digest | +--------------+ dlist is a digest list containing the digest of file1, file2 and file3. In the intended scenario, it is generated by a software vendor at the end of the building process, and retrieved by the administrator of the system where the digest list is loaded. entry# 1st boot 2nd boot 3rd boot +----+---------------+ +----+---------------+ +----+---------------+ 0: | 11 | dlist measur. | | 11 | dlist measur. | | 11 | dlist measur. | +----+---------------+ +----+---------------+ +----+---------------+ 1: < file1 measur. skip > < file3 measur. skip > < file2 measur. skip > 2: < file2 measur. skip > < file2 measur. skip > < file3 measur. skip > +----+---------------+ 3: < file3 measur. skip > < file1 measur. skip > | 11 | file4 measur. | +----+---------------+ PCR: Extend = Extend != Extend dlist dlist dlist, file4 The first entry in the measurement list contains the digest of the digest list uploaded to the kernel at kernel initialization time. When a file is accessed, IMA queries DIGLIM with the calculated file digest and, if it is found, IMA skips the measurement. Thus, the only information sent to remote verifiers are: the list of files that could possibly be accessed (from the digest list), but not if they were accessed and when; the measurement of unknown files. Despite providing less information, this solution has the advantage that the good system state (i.e. when only file1, file2 and file3 are accessed) now can be represented with a deterministic PCR value (the PCR is extended only with the measurement of the digest list). Also, the bad system state can still be distinguished from the good state (the PCR is extended also with the measurement of file4). If a TPM key is bound to the good PCR value, the TPM would allow the key to be used if file1, file2 or file3 are accessed, regardless of the sequence in which they are accessed (the PCR value does not change), and would revoke the permission when the unknown file4 is accessed (the PCR value changes). If a system is able to establish a TLS connection with a peer, this implicitly means that the system was in a good state (i.e. file4 was not accessed, otherwise the TPM would have denied the usage of the TPM key due to the key policy). Benefits for IMA Appraisal Extending secure boot to applications means being able to verify the provenance of files accessed. IMA does it by verifying file signatures with a key that it trusts, which requires Linux distribution vendors to additionally include in the package header a signature for each file that must be verified (there is the dedicated RPMTAG_FILESIGNATURES section in the RPM header). The proposed approach would be instead to verify data provenance from already available metadata (file digests) in existing packages. IMA would verify the signature of package metadata and search file digests extracted from package metadata and added to the hash table in the kernel. For RPMs, file digests can be found in the RPMTAG_FILEDIGESTS section of RPMTAG_IMMUTABLE, whose signature is in RPMTAG_RSAHEADER. For DEBs, file digests (unsafe to use due to a weak digest algorithm) can be found in the md5sum file, which can be indirectly verified from Release.gpg. The following figure highlights the differences between the current and the proposed approach. IMA appraisal (current solution, with file signatures): appraise +-----------+ V | +-------------------------+-----+ +-------+-----+ | | RPM header | | ima rpm | file1 | sig | | | ... | | plugin +-------+-----+ +-----+ | file1 sig [to be added] | sig |--------> ... | IMA | | ... | | +-------+-----+ +-----+ | fileN sig [to be added] | | | fileN | sig | +-------------------------+-----+ +-------+-----+ In this case, file signatures must be added to the RPM header, so that the ima rpm plugin can extract them together with the file content. The RPM header signature is not used. IMA appraisal (with DIGLIM): kernel hash table with RPM header content +---+ +--------------+ | |--->| file1 digest | +---+ +--------------+ ... +---+ appraise (file1) | | <--------------+ +----------------+-----+ +---+ | | RPM header | | ^ | | ... | | digest_list | | | file1 digest | sig | rpm plugin | +-------+ +-----+ | ... | |-------------+--->| file1 | | IMA | | fileN digest | | +-------+ +-----+ +----------------+-----+ | ^ | +------------------------------------+ appraise (RPM header) In this case, the RPM header is used as it is, and its signature is used for IMA appraisal. Then, the digest_list rpm plugin executes the user space parser to parse the RPM header and add the extracted digests to an hash table in the kernel. IMA appraisal of the files in the RPM package consists in searching their digest in the hash table. Other than reusing available information as digest list, another advantage is the lower computational overhead compared to the solution with file signatures (only one signature verification for many files and digest lookup, instead of per file signature verification, see Preliminary Performance Evaluation for more details). Lifecycle The lifecycle of DIGLIM is represented in the following figure: Vendor premises (release process with modifications): +------------+ +-----------------------+ +------------------------+ | 1. build a | | 2. generate and sign | | 3. publish the package | | package |-->| a digest list from |-->| and digest list in | | | | packaged files | | a repository | +------------+ +-----------------------+ +------------------------+ | | User premises: | V +---------------------+ +------------------------+ +-----------------+ | 6. use digest lists | | 5. download the digest | | 4. download and | | for measurement |<--| list and upload to |<--| install the | | and/or appraisal | | the kernel | | package | +---------------------+ +------------------------+ +-----------------+ The figure above represents all the steps when a digest list is generated separately. However, as mentioned in Contribution, in most cases existing packages can be already used as a source for digest lists, limiting the effort for software vendors. If, for example, RPMs are used as a source for digest lists, the figure above becomes: Vendor premises (release process without modifications): +------------+ +------------------------+ | 1. build a | | 2. publish the package | | package |-->| in a repository |---------------------+ | | | | | +------------+ +------------------------+ | | | User premises: | V +---------------------+ +------------------------+ +-----------------+ | 5. use digest lists | | 4. extract digest list | | 3. download and | | for measurement |<--| from the package |<--| install the | | and/or appraisal | | and upload to the | | package | | | | kernel | | | +---------------------+ +------------------------+ +-----------------+ Step 4 can be performed with the digest_list rpm plugin and the user space parser, without changes to rpm itself. Security Assumptions As mentioned in the Introduction, DIGLIM will be primarily used in conjunction with IMA to enforce a mandatory policy on all user space processes, including those owned by root. Even root, in a system with a locked-down kernel, cannot affect the enforcement of the mandatory policy or, if changes are permitted, it cannot do so without being detected. Given that the target of the enforcement are user space processes, DIGLIM cannot be placed in the target, as a Mandatory Access Control (MAC) design is required to have the components responsible to enforce the mandatory policy separated from the target. While locking-down a system and limiting actions with a mandatory policy is generally perceived by users as an obstacle, it has noteworthy benefits for the users themselves. First, it would timely block attempts by malicious software to steal or misuse user assets. Although users could query the package managers to detect them, detection would happen after the fact, or it wouldn't happen at all if the malicious software tampered with package managers. With a mandatory policy enforced by the kernel, users would still be able to decide which software they want to be executed except that, unlike package managers, the kernel is not affected by user space processes or root. Second, it might make systems more easily verifiable from outside, due to the limited actions the system allows. When users connect to a server, not only they would be able to verify the server identity, which is already possible with communication protocols like TLS, but also if the software running on that server can be trusted to handle their sensitive data. Adoption A former version of DIGLIM is used in the following OSes: - openEuler 20.09 https://github.com/openeuler-mirror/kernel/tree/openEuler-20.09 - openEuler 21.03 https://github.com/openeuler-mirror/kernel/tree/openEuler-21.03 Originally, DIGLIM was part of IMA (known as IMA Digest Lists). In this version, it has been redesigned as a standalone module with an API that makes its functionality accessible by IMA and, eventually, other subsystems. User Space Support Digest lists can be generated and managed with digest-list-tools: https://github.com/openeuler-mirror/digest-list-tools It includes two main applications: - gen_digest_lists: generates digest lists from files in the filesystem or from the RPM database (more digest list sources can be supported); - manage_digest_lists: converts and uploads digest lists to the kernel. Integration with rpm is done with the digest_list plugin: https://gitee.com/src-openeuler/rpm/blob/master/Add-digest-list-plugin.patch This plugin writes the RPM header and its signature to a file, so that the file is ready to be appraised by IMA, and calls the user space parser to convert and upload the digest list to the kernel. Simple Usage Example (Tested with Fedora 33) 1. Digest list generation (RPM headers and their signature are copied to the specified directory): # mkdir /etc/digest_lists # gen_digest_lists -t file -f rpm+db -d /etc/digest_lists -o add 2. Digest list upload with the user space parser: # manage_digest_lists -p add-digest -d /etc/digest_lists 3. First digest list query: # echo sha256-$(sha256sum /bin/cat) > /sys/kernel/security/integrity/diglim/digest_query # cat /sys/kernel/security/integrity/diglim/digest_query sha256-[...]-0-file_list-rpm-coreutils-8.32-18.fc33.x86_64 (actions: 0): version: 1, algo: sha256, type: 2, modifiers: 1, count: 106, datalen: 3392 4. Second digest list query: # echo sha256-$(sha256sum /bin/zip) > /sys/kernel/security/integrity/diglim/digest_query # cat /sys/kernel/security/integrity/diglim/digest_query sha256-[...]-0-file_list-rpm-zip-3.0-27.fc33.x86_64 (actions: 0): version: 1, algo: sha256, type: 2, modifiers: 1, count: 4, datalen: 128 Preliminary Performance Evaluation This section provides an initial estimation of the overhead introduced by DIGLIM. The estimation has been performed on a Fedora 33 virtual machine with 1447 packages installed. The virtual machine has 16 vCPU (host CPU: AMD Ryzen Threadripper PRO 3955WX 16-Cores) and 2G of RAM (host memory: 64G). The virtual machine also has a vTPM with libtpms and swtpm as backend. After writing the RPM headers to files, the size of the directory containing them is 36M. After converting the RPM headers to the compact digest list, the size of the data being uploaded to the kernel is 3.6M. The time to load the entire RPM database is 0.628s. After loading the digest lists to the kernel, the slab usage due to indexing is (obtained with slab_nomerge in the kernel command line): OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME 118144 118144 100% 0,03K 923 128 3692K digest_list_item_ref_cache 102400 102400 100% 0,03K 800 128 3200K digest_item_cache 2646 2646 100% 0,09K 63 42 252K digest_list_item_cache The stats, obtained from the digests_count interface, introduced later, are: Parser digests: 0 File digests: 99100 Metadata digests: 0 Digest list digests: 1423 On this installation, this would be the worst case in which all files are measured and/or appraised, which is currently not recommended without enforcing an integrity policy protecting mutable files. Infoflow LSM is a component to accomplish this task: https://patchwork.kernel.org/project/linux-integrity/cover/20190818235745.1417-1-roberto.sassu@huawei.com/ The first manageable goal of IMA with DIGLIM is to use an execution policy, with measurement and/or appraisal of files executed or mapped in memory as executable (in addition to kernel modules and firmware). In this case, the digest list contains the digest only for those files. The numbers above change as follows. After converting the RPM headers to the compact digest list, the size of the data being uploaded to the kernel is 208K. The time to load the digest of binaries and shared libraries is 0.062s. After loading the digest lists to the kernel, the slab usage due to indexing is: OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME 7168 7168 100% 0,03K 56 128 224K digest_list_item_ref_cache 7168 7168 100% 0,03K 56 128 224K digest_item_cache 1134 1134 100% 0,09K 27 42 108K digest_list_item_cache The stats, obtained from the digests_count interface, are: Parser digests: 0 File digests: 5986 Metadata digests: 0 Digest list digests: 1104 Comparison with IMA This section compares the performance between the current solution for IMA measurement and appraisal, and IMA with DIGLIM. Workload A (without DIGLIM): 1. cat file[0-5985] > /dev/null Workload B (with DIGLIM): 1. echo $PWD/0-file_list-compact-file[0-1103] > <securityfs>/integrity/diglim/digest_list_add 2. cat file[0-5985] > /dev/null Workload A execution time without IMA policy: real 0m0,155s user 0m0,008s sys 0m0,066s Measurement IMA policy: measure fowner=2000 func=FILE_CHECK mask=MAY_READ use_diglim=allow pcr=11 ima_template=ima-sig use_diglim is a policy keyword not yet supported by IMA. Workload A execution time with IMA and 5986 files with signature measured: real 0m8,273s user 0m0,008s sys 0m2,537s Workload B execution time with IMA, 1104 digest lists with signature measured and uploaded to the kernel, and 5986 files with signature accessed but not measured (due to the file digest being found in the hash table): real 0m1,837s user 0m0,036s sys 0m0,583s Appraisal IMA policy: appraise fowner=2000 func=FILE_CHECK mask=MAY_READ use_diglim=allow use_diglim is a policy keyword not yet supported by IMA. Workload A execution time with IMA and 5986 files with file signature appraised: real 0m2,197s user 0m0,011s sys 0m2,022s Workload B execution time with IMA, 1104 digest lists with signature appraised and uploaded to the kernel, and with 5986 files with signature not verified (due to the file digest being found in the hash table): real 0m0,982s user 0m0,020s sys 0m0,865s Changelog v1: - remove 'ima: Add digest, algo, measured parameters to ima_measure_critical_data()', replaced by: https://lore.kernel.org/linux-integrity/20210705090922.3321178-1-roberto.sassu@huawei.com/ - add 'Lifecycle' subsection to better clarify how digest lists are generated and used (suggested by Greg KH) - remove 'Possible Usages' subsection and add 'Benefits for IMA Measurement' and 'Benefits for IMA Appraisal' subsubsections - add 'Preliminary Performance Evaluation' subsection - declare digest_offset and hdr_offset in the digest_list_item_ref structure as u32 (sufficient for digest lists of 4G) to make room for a list_head structure (digest_list_item_ref size: 32) - implement digest list reference management with a linked list instead of an array - reorder structure members for better alignment (suggested by Mauro) - rename digest_lookup() to __digest_lookup() (suggested by Mauro) - introduce an object cache for each defined structure - replace atomic_long_t with unsigned long in h_table structure definition (suggested by Greg KH) - remove GPL2 license text and file names (suggested by Greg KH) - ensure that the _reserved field of compact_list_hdr is equal to zero (suggested by Greg KH) - dynamically allocate the buffer in digest_lists_show_htable_len() to avoid frame size warning (reported by kernel test robot, dynamic allocation suggested by Mauro) - split documentation in multiple files and reference the source code (suggested by Mauro) - use #ifdef in include/linux/diglim.h - improve generation of event name for IMA measurements - add new patch to introduce the 'Remote Attestation' section in the documentation - fix assignment of actions variable in digest_list_read() and digest_list_write() - always release dentry reference when digest_list_get_secfs_files() is called - rewrite add/del and query interfaces to take advantage of m->private - prevent deletion of a digest list only if there are actions done at addition time that are not currently being performed - fix doc warnings (replace Returns with Return:) - perform queries of digest list digests in the existing tests - add new tests: digest_list_add_del_test_file_upload_measured, digest_list_check_measurement_list_test_file_upload and digest_list_check_measurement_list_test_buffer_upload - don't return a value from digest_del(), digest_list_ref_del, and digest_list_del() - improve Makefile for tests Roberto Sassu (12): diglim: Overview diglim: Basic definitions diglim: Objects diglim: Methods diglim: Parser diglim: Interfaces - digest_list_add, digest_list_del diglim: Interfaces - digest_lists_loaded diglim: Interfaces - digest_label diglim: Interfaces - digest_query diglim: Interfaces - digests_count diglim: Remote Attestation diglim: Tests .../security/diglim/architecture.rst | 45 + .../security/diglim/implementation.rst | 255 +++ Documentation/security/diglim/index.rst | 14 + .../security/diglim/introduction.rst | 631 ++++++++ .../security/diglim/remote_attestation.rst | 87 ++ Documentation/security/diglim/tests.rst | 66 + Documentation/security/index.rst | 1 + MAINTAINERS | 19 + include/linux/diglim.h | 28 + include/linux/kernel_read_file.h | 1 + include/uapi/linux/diglim.h | 51 + security/integrity/Kconfig | 1 + security/integrity/Makefile | 1 + security/integrity/diglim/Kconfig | 11 + security/integrity/diglim/Makefile | 8 + security/integrity/diglim/diglim.h | 157 ++ security/integrity/diglim/fs.c | 782 ++++++++++ security/integrity/diglim/methods.c | 499 ++++++ security/integrity/diglim/parser.c | 274 ++++ security/integrity/integrity.h | 4 + tools/testing/selftests/Makefile | 1 + tools/testing/selftests/diglim/Makefile | 19 + tools/testing/selftests/diglim/common.c | 115 ++ tools/testing/selftests/diglim/common.h | 31 + tools/testing/selftests/diglim/config | 3 + tools/testing/selftests/diglim/selftest.c | 1382 +++++++++++++++++ 26 files changed, 4486 insertions(+) create mode 100644 Documentation/security/diglim/architecture.rst create mode 100644 Documentation/security/diglim/implementation.rst create mode 100644 Documentation/security/diglim/index.rst create mode 100644 Documentation/security/diglim/introduction.rst create mode 100644 Documentation/security/diglim/remote_attestation.rst create mode 100644 Documentation/security/diglim/tests.rst create mode 100644 include/linux/diglim.h create mode 100644 include/uapi/linux/diglim.h create mode 100644 security/integrity/diglim/Kconfig create mode 100644 security/integrity/diglim/Makefile create mode 100644 security/integrity/diglim/diglim.h create mode 100644 security/integrity/diglim/fs.c create mode 100644 security/integrity/diglim/methods.c create mode 100644 security/integrity/diglim/parser.c create mode 100644 tools/testing/selftests/diglim/Makefile create mode 100644 tools/testing/selftests/diglim/common.c create mode 100644 tools/testing/selftests/diglim/common.h create mode 100644 tools/testing/selftests/diglim/config create mode 100644 tools/testing/selftests/diglim/selftest.c