| Message ID | 20220406015337.4000739-5-eric.snowberg@oracle.com |
|---|---|
| State | New |
| Headers | show |
| Series | Add CA enforcement keyring restrictions | expand |
On Tue, 2022-04-05 at 21:53 -0400, Eric Snowberg wrote: > Some subsystems are interested in knowing if keys within a keyring could > be used as a foundation of a root of trust. Introduce a new builtin root > of trust key flag. Unfortunately a root of trust is not something that can simply be built into a certificate. Roots of trust are normally established based on HW. The root of trust for the "builtin_trusted_keys" is established for systems with secure boot enabled by verifying the signature chain of trust up to and including the kernel image's signature. Similarly, the root of trust for keys on the "secondary_trusted_keys" is based on all certificates being signed by a key on the "builtin_trusted_keys" keyring or other keys on the "secondary_trusted_keys" keyring. Defining a new variable claiming that a root-ca with cert signing usage on any keyring is a root of trust is just wrong. > > The first type of key to use this is X.509. When a X.509 certificate > is self signed, has the kernCertSign Key Usage set and contains the > CA bit set this new flag is set. > > Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com> > > diff --git a/include/linux/key.h b/include/linux/key.h > index 7febc4881363..97f6a1f86a27 100644 > --- a/include/linux/key.h > +++ b/include/linux/key.h > @@ -230,6 +230,7 @@ struct key { > #define KEY_FLAG_ROOT_CAN_INVAL 7 /* set if key can be invalidated by root without permission */ > #define KEY_FLAG_KEEP 8 /* set if key should not be removed */ > #define KEY_FLAG_UID_KEYRING 9 /* set if key is a user or user session keyring */ > +#define KEY_FLAG_BUILTIN_ROT 10 /* set if key is a builtin Root of Trust key */ > > /* the key type and key description string > * - the desc is used to match a key against search criteria > @@ -290,6 +291,7 @@ extern struct key *key_alloc(struct key_type *type, > #define KEY_ALLOC_BYPASS_RESTRICTION 0x0008 /* Override the check on restricted keyrings */ > #define KEY_ALLOC_UID_KEYRING 0x0010 /* allocating a user or user session keyring */ > #define KEY_ALLOC_SET_KEEP 0x0020 /* Set the KEEP flag on the key/keyring */ > +#define KEY_ALLOC_BUILT_IN_ROT 0x0040 /* Add builtin root of trust key */ Since the concept of root of trust is not generic, but limited to specific keyrings, the root CA certificate signing keys on the "machine" keyring need to be identified. Similar to the KEY_ALLOC_BUILT_IN/KEY_FLAG_BUILTIN, new flags KEY_ALLOC_MACHINE/KEY_FLAG_MACHINE should be defined instead. thanks, Mimi
> On Apr 8, 2022, at 8:40 AM, Mimi Zohar <zohar@linux.ibm.com> wrote: > > On Tue, 2022-04-05 at 21:53 -0400, Eric Snowberg wrote: >> >> The first type of key to use this is X.509. When a X.509 certificate >> is self signed, has the kernCertSign Key Usage set and contains the >> CA bit set this new flag is set. >> >> Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com> >> >> diff --git a/include/linux/key.h b/include/linux/key.h >> index 7febc4881363..97f6a1f86a27 100644 >> --- a/include/linux/key.h >> +++ b/include/linux/key.h >> @@ -230,6 +230,7 @@ struct key { >> #define KEY_FLAG_ROOT_CAN_INVAL 7 /* set if key can be invalidated by root without permission */ >> #define KEY_FLAG_KEEP 8 /* set if key should not be removed */ >> #define KEY_FLAG_UID_KEYRING 9 /* set if key is a user or user session keyring */ >> +#define KEY_FLAG_BUILTIN_ROT 10 /* set if key is a builtin Root of Trust key */ >> >> /* the key type and key description string >> * - the desc is used to match a key against search criteria >> @@ -290,6 +291,7 @@ extern struct key *key_alloc(struct key_type *type, >> #define KEY_ALLOC_BYPASS_RESTRICTION 0x0008 /* Override the check on restricted keyrings */ >> #define KEY_ALLOC_UID_KEYRING 0x0010 /* allocating a user or user session keyring */ >> #define KEY_ALLOC_SET_KEEP 0x0020 /* Set the KEEP flag on the key/keyring */ >> +#define KEY_ALLOC_BUILT_IN_ROT 0x0040 /* Add builtin root of trust key */ > > Since the concept of root of trust is not generic, but limited to > specific keyrings, the root CA certificate signing keys on the > "machine" keyring need to be identified. Similar to the > KEY_ALLOC_BUILT_IN/KEY_FLAG_BUILTIN, new flags > KEY_ALLOC_MACHINE/KEY_FLAG_MACHINE should be defined instead. I’m open to renaming these, however this name change seems confusing to me. This flag gets set when the X.509 certificate contains the three CA requirements identified above. The remaining keys in the machine keyring can be used for anything else. Plus this flag can be set for keys loaded into the secondary trusted keyring (6th patch in the series). When an intermediate CA gets loaded into the secondary, the flag is set as well.
On Fri, 2022-04-08 at 15:27 +0000, Eric Snowberg wrote: > > > On Apr 8, 2022, at 8:40 AM, Mimi Zohar <zohar@linux.ibm.com> wrote: > > > > On Tue, 2022-04-05 at 21:53 -0400, Eric Snowberg wrote: > >> > >> The first type of key to use this is X.509. When a X.509 certificate > >> is self signed, has the kernCertSign Key Usage set and contains the > >> CA bit set this new flag is set. > >> > >> Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com> > >> > >> diff --git a/include/linux/key.h b/include/linux/key.h > >> index 7febc4881363..97f6a1f86a27 100644 > >> --- a/include/linux/key.h > >> +++ b/include/linux/key.h > >> @@ -230,6 +230,7 @@ struct key { > >> #define KEY_FLAG_ROOT_CAN_INVAL 7 /* set if key can be invalidated by root without permission */ > >> #define KEY_FLAG_KEEP 8 /* set if key should not be removed */ > >> #define KEY_FLAG_UID_KEYRING 9 /* set if key is a user or user session keyring */ > >> +#define KEY_FLAG_BUILTIN_ROT 10 /* set if key is a builtin Root of Trust key */ > >> > >> /* the key type and key description string > >> * - the desc is used to match a key against search criteria > >> @@ -290,6 +291,7 @@ extern struct key *key_alloc(struct key_type *type, > >> #define KEY_ALLOC_BYPASS_RESTRICTION 0x0008 /* Override the check on restricted keyrings */ > >> #define KEY_ALLOC_UID_KEYRING 0x0010 /* allocating a user or user session keyring */ > >> #define KEY_ALLOC_SET_KEEP 0x0020 /* Set the KEEP flag on the key/keyring */ > >> +#define KEY_ALLOC_BUILT_IN_ROT 0x0040 /* Add builtin root of trust key */ > > > > Since the concept of root of trust is not generic, but limited to > > specific keyrings, the root CA certificate signing keys on the > > "machine" keyring need to be identified. Similar to the > > KEY_ALLOC_BUILT_IN/KEY_FLAG_BUILTIN, new flags > > KEY_ALLOC_MACHINE/KEY_FLAG_MACHINE should be defined instead. > > I’m open to renaming these, however this name change seems confusing to me. > This flag gets set when the X.509 certificate contains the three CA requirements > identified above. The remaining keys in the machine keyring can be used for > anything else. Renaming the flag to KEY_ALLOC_MACHINE/KEY_FLAG_MACHINE differentiates between the "builtin" keys from the "machine" keys. The trust models are very different. > Plus this flag can be set for keys loaded into the secondary trusted > keyring (6th patch in the series). When an intermediate CA gets loaded into the > secondary, the flag is set as well. Please include a full explanation with the motivation in the patch description as to why support for intermediary CAs is required for the "end-user" use case. thanks, Mimi
> On Apr 8, 2022, at 10:55 AM, Mimi Zohar <zohar@linux.ibm.com> wrote: > > On Fri, 2022-04-08 at 15:27 +0000, Eric Snowberg wrote: >> >>> On Apr 8, 2022, at 8:40 AM, Mimi Zohar <zohar@linux.ibm.com> wrote: >>> >>> On Tue, 2022-04-05 at 21:53 -0400, Eric Snowberg wrote: >>>> >>>> The first type of key to use this is X.509. When a X.509 certificate >>>> is self signed, has the kernCertSign Key Usage set and contains the >>>> CA bit set this new flag is set. >>>> >>>> Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com> >>>> >>>> diff --git a/include/linux/key.h b/include/linux/key.h >>>> index 7febc4881363..97f6a1f86a27 100644 >>>> --- a/include/linux/key.h >>>> +++ b/include/linux/key.h >>>> @@ -230,6 +230,7 @@ struct key { >>>> #define KEY_FLAG_ROOT_CAN_INVAL 7 /* set if key can be invalidated by root without permission */ >>>> #define KEY_FLAG_KEEP 8 /* set if key should not be removed */ >>>> #define KEY_FLAG_UID_KEYRING 9 /* set if key is a user or user session keyring */ >>>> +#define KEY_FLAG_BUILTIN_ROT 10 /* set if key is a builtin Root of Trust key */ >>>> >>>> /* the key type and key description string >>>> * - the desc is used to match a key against search criteria >>>> @@ -290,6 +291,7 @@ extern struct key *key_alloc(struct key_type *type, >>>> #define KEY_ALLOC_BYPASS_RESTRICTION 0x0008 /* Override the check on restricted keyrings */ >>>> #define KEY_ALLOC_UID_KEYRING 0x0010 /* allocating a user or user session keyring */ >>>> #define KEY_ALLOC_SET_KEEP 0x0020 /* Set the KEEP flag on the key/keyring */ >>>> +#define KEY_ALLOC_BUILT_IN_ROT 0x0040 /* Add builtin root of trust key */ >>> >>> Since the concept of root of trust is not generic, but limited to >>> specific keyrings, the root CA certificate signing keys on the >>> "machine" keyring need to be identified. Similar to the >>> KEY_ALLOC_BUILT_IN/KEY_FLAG_BUILTIN, new flags >>> KEY_ALLOC_MACHINE/KEY_FLAG_MACHINE should be defined instead. >> >> I’m open to renaming these, however this name change seems confusing to me. >> This flag gets set when the X.509 certificate contains the three CA requirements >> identified above. The remaining keys in the machine keyring can be used for >> anything else. > > Renaming the flag to KEY_ALLOC_MACHINE/KEY_FLAG_MACHINE differentiates > between the "builtin" keys from the "machine" keys. The trust models > are very different. Isn’t the trust model the same for machine and secondary keys? Both are supplied by the end-user. That is why I’m confused by naming something _MACHINE when it applies to more than one keyring. >> Plus this flag can be set for keys loaded into the secondary trusted >> keyring (6th patch in the series). When an intermediate CA gets loaded into the >> secondary, the flag is set as well. > > Please include a full explanation with the motivation in the patch > description as to why support for intermediary CAs is required for the > "end-user" use case. Ok, I can add it. I thought this was an expectation, based on the help section of IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY: " Intermediate keys between those the kernel has compiled in and the IMA keys to be added may be added to the system secondary keyring, provided they are validly signed by a key already resident in the built-in or secondary trusted keyrings."
On Fri, 2022-04-08 at 17:34 +0000, Eric Snowberg wrote: > > > On Apr 8, 2022, at 10:55 AM, Mimi Zohar <zohar@linux.ibm.com> wrote: > > > > On Fri, 2022-04-08 at 15:27 +0000, Eric Snowberg wrote: > >> > >>> On Apr 8, 2022, at 8:40 AM, Mimi Zohar <zohar@linux.ibm.com> wrote: > >>> > >>> On Tue, 2022-04-05 at 21:53 -0400, Eric Snowberg wrote: > >>>> > >>>> The first type of key to use this is X.509. When a X.509 certificate > >>>> is self signed, has the kernCertSign Key Usage set and contains the > >>>> CA bit set this new flag is set. > >>>> > >>>> Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com> > >>>> > >>>> diff --git a/include/linux/key.h b/include/linux/key.h > >>>> index 7febc4881363..97f6a1f86a27 100644 > >>>> --- a/include/linux/key.h > >>>> +++ b/include/linux/key.h > >>>> @@ -230,6 +230,7 @@ struct key { > >>>> #define KEY_FLAG_ROOT_CAN_INVAL 7 /* set if key can be invalidated by root without permission */ > >>>> #define KEY_FLAG_KEEP 8 /* set if key should not be removed */ > >>>> #define KEY_FLAG_UID_KEYRING 9 /* set if key is a user or user session keyring */ > >>>> +#define KEY_FLAG_BUILTIN_ROT 10 /* set if key is a builtin Root of Trust key */ > >>>> > >>>> /* the key type and key description string > >>>> * - the desc is used to match a key against search criteria > >>>> @@ -290,6 +291,7 @@ extern struct key *key_alloc(struct key_type *type, > >>>> #define KEY_ALLOC_BYPASS_RESTRICTION 0x0008 /* Override the check on restricted keyrings */ > >>>> #define KEY_ALLOC_UID_KEYRING 0x0010 /* allocating a user or user session keyring */ > >>>> #define KEY_ALLOC_SET_KEEP 0x0020 /* Set the KEEP flag on the key/keyring */ > >>>> +#define KEY_ALLOC_BUILT_IN_ROT 0x0040 /* Add builtin root of trust key */ > >>> > >>> Since the concept of root of trust is not generic, but limited to > >>> specific keyrings, the root CA certificate signing keys on the > >>> "machine" keyring need to be identified. Similar to the > >>> KEY_ALLOC_BUILT_IN/KEY_FLAG_BUILTIN, new flags > >>> KEY_ALLOC_MACHINE/KEY_FLAG_MACHINE should be defined instead. > >> > >> I’m open to renaming these, however this name change seems confusing to me. > >> This flag gets set when the X.509 certificate contains the three CA requirements > >> identified above. The remaining keys in the machine keyring can be used for > >> anything else. > > > > Renaming the flag to KEY_ALLOC_MACHINE/KEY_FLAG_MACHINE differentiates > > between the "builtin" keys from the "machine" keys. The trust models > > are very different. > > Isn’t the trust model the same for machine and secondary keys? Both are supplied by > the end-user. That is why I’m confused by naming something _MACHINE when it applies > to more than one keyring. True both are supplied by the end-user, but the trust models are different. In one case the certificates are coming indirectly from firmware, while in the other case the certificates would be limited to certificates signed by the initial firmware certificates. Loading only root-CA signing key certificates onto the "machine" keyring highlights and enforces the different types of trust. > > >> Plus this flag can be set for keys loaded into the secondary trusted > >> keyring (6th patch in the series). When an intermediate CA gets loaded into the > >> secondary, the flag is set as well. > > > > Please include a full explanation with the motivation in the patch > > description as to why support for intermediary CAs is required for the > > "end-user" use case. > > Ok, I can add it. I thought this was an expectation, based on the help section of > IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY: > > " Intermediate keys between those the kernel has compiled in and the > IMA keys to be added may be added to the system secondary keyring, > provided they are validly signed by a key already resident in the > built-in or secondary trusted keyrings." This paragraph refers to keys on the "builtin_trusted_keys" keyring. The concept would need to be expanded to include keys on the "machine" keyring. Since support for intermediary CA keys isn't required for the simple "end-user" use case, the motivation needs to be provided. thanks, Mimi
> On Apr 8, 2022, at 12:49 PM, Mimi Zohar <zohar@linux.ibm.com> wrote: > > On Fri, 2022-04-08 at 17:34 +0000, Eric Snowberg wrote: >> >>> On Apr 8, 2022, at 10:55 AM, Mimi Zohar <zohar@linux.ibm.com> wrote: >>> >>> On Fri, 2022-04-08 at 15:27 +0000, Eric Snowberg wrote: >>>> >>>>> On Apr 8, 2022, at 8:40 AM, Mimi Zohar <zohar@linux.ibm.com> wrote: >>>>> >>>>> On Tue, 2022-04-05 at 21:53 -0400, Eric Snowberg wrote: >>>>>> >>>>>> The first type of key to use this is X.509. When a X.509 certificate >>>>>> is self signed, has the kernCertSign Key Usage set and contains the >>>>>> CA bit set this new flag is set. >>>>>> >>>>>> Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com> >>>>>> >>>>>> diff --git a/include/linux/key.h b/include/linux/key.h >>>>>> index 7febc4881363..97f6a1f86a27 100644 >>>>>> --- a/include/linux/key.h >>>>>> +++ b/include/linux/key.h >>>>>> @@ -230,6 +230,7 @@ struct key { >>>>>> #define KEY_FLAG_ROOT_CAN_INVAL 7 /* set if key can be invalidated by root without permission */ >>>>>> #define KEY_FLAG_KEEP 8 /* set if key should not be removed */ >>>>>> #define KEY_FLAG_UID_KEYRING 9 /* set if key is a user or user session keyring */ >>>>>> +#define KEY_FLAG_BUILTIN_ROT 10 /* set if key is a builtin Root of Trust key */ >>>>>> >>>>>> /* the key type and key description string >>>>>> * - the desc is used to match a key against search criteria >>>>>> @@ -290,6 +291,7 @@ extern struct key *key_alloc(struct key_type *type, >>>>>> #define KEY_ALLOC_BYPASS_RESTRICTION 0x0008 /* Override the check on restricted keyrings */ >>>>>> #define KEY_ALLOC_UID_KEYRING 0x0010 /* allocating a user or user session keyring */ >>>>>> #define KEY_ALLOC_SET_KEEP 0x0020 /* Set the KEEP flag on the key/keyring */ >>>>>> +#define KEY_ALLOC_BUILT_IN_ROT 0x0040 /* Add builtin root of trust key */ >>>>> >>>>> Since the concept of root of trust is not generic, but limited to >>>>> specific keyrings, the root CA certificate signing keys on the >>>>> "machine" keyring need to be identified. Similar to the >>>>> KEY_ALLOC_BUILT_IN/KEY_FLAG_BUILTIN, new flags >>>>> KEY_ALLOC_MACHINE/KEY_FLAG_MACHINE should be defined instead. >>>> >>>> I’m open to renaming these, however this name change seems confusing to me. >>>> This flag gets set when the X.509 certificate contains the three CA requirements >>>> identified above. The remaining keys in the machine keyring can be used for >>>> anything else. >>> >>> Renaming the flag to KEY_ALLOC_MACHINE/KEY_FLAG_MACHINE differentiates >>> between the "builtin" keys from the "machine" keys. The trust models >>> are very different. >> >> Isn’t the trust model the same for machine and secondary keys? Both are supplied by >> the end-user. That is why I’m confused by naming something _MACHINE when it applies >> to more than one keyring. > > True both are supplied by the end-user, but the trust models are > different. I think I need more information here, I’m not seeing how they are different trust models. > In one case the certificates are coming indirectly from > firmware, Any kernel signed by a cert in the MokList will boot. The very thing the machine keyring contains. For example, if a user has a cert (CA bit set false, keyCertSign not set, and it isn’t self signed), they can use insert-sys-cert to get it into their kernel. They can then sign the kernel with any key in their MokList. Why would we want to treat this key different if it was injected into the kernel verses coming in through the machine keyring? I can see the desire to have a root of trust all the way back to the root CA. What I can’t see is if we ignore this for certain keyrings. > while in the other case the certificates would be limited to > certificates signed by the initial firmware certificates. Loading only > root-CA signing key certificates onto the "machine" keyring highlights > and enforces the different types of trust. If the root-CA cert must contain keyCertSign, I don’t see the point in loading only root-CA certs either. Why would we want to prevent a code signing cert with the CA bit set from loading into the machine keyring? A code signing cert should be allowed to validate a kernel module, but It should not be allowed to validate other certs.
On Fri, 2022-04-08 at 21:59 +0000, Eric Snowberg wrote: > > On Apr 8, 2022, at 12:49 PM, Mimi Zohar <zohar@linux.ibm.com> wrote: > > > > On Fri, 2022-04-08 at 17:34 +0000, Eric Snowberg wrote: > >> > >>> On Apr 8, 2022, at 10:55 AM, Mimi Zohar <zohar@linux.ibm.com> wrote: > >>> > >>> On Fri, 2022-04-08 at 15:27 +0000, Eric Snowberg wrote: > >>>> > >>>>> On Apr 8, 2022, at 8:40 AM, Mimi Zohar <zohar@linux.ibm.com> wrote: > >>>>> > >>>>> On Tue, 2022-04-05 at 21:53 -0400, Eric Snowberg wrote: > >>>>>> > >>>>>> The first type of key to use this is X.509. When a X.509 certificate > >>>>>> is self signed, has the kernCertSign Key Usage set and contains the > >>>>>> CA bit set this new flag is set. > >>>>>> > >>>>>> Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com> > >>>>>> > >>>>>> diff --git a/include/linux/key.h b/include/linux/key.h > >>>>>> index 7febc4881363..97f6a1f86a27 100644 > >>>>>> --- a/include/linux/key.h > >>>>>> +++ b/include/linux/key.h > >>>>>> @@ -230,6 +230,7 @@ struct key { > >>>>>> #define KEY_FLAG_ROOT_CAN_INVAL 7 /* set if key can be invalidated by root without permission */ > >>>>>> #define KEY_FLAG_KEEP 8 /* set if key should not be removed */ > >>>>>> #define KEY_FLAG_UID_KEYRING 9 /* set if key is a user or user session keyring */ > >>>>>> +#define KEY_FLAG_BUILTIN_ROT 10 /* set if key is a builtin Root of Trust key */ > >>>>>> > >>>>>> /* the key type and key description string > >>>>>> * - the desc is used to match a key against search criteria > >>>>>> @@ -290,6 +291,7 @@ extern struct key *key_alloc(struct key_type *type, > >>>>>> #define KEY_ALLOC_BYPASS_RESTRICTION 0x0008 /* Override the check on restricted keyrings */ > >>>>>> #define KEY_ALLOC_UID_KEYRING 0x0010 /* allocating a user or user session keyring */ > >>>>>> #define KEY_ALLOC_SET_KEEP 0x0020 /* Set the KEEP flag on the key/keyring */ > >>>>>> +#define KEY_ALLOC_BUILT_IN_ROT 0x0040 /* Add builtin root of trust key */ > >>>>> > >>>>> Since the concept of root of trust is not generic, but limited to > >>>>> specific keyrings, the root CA certificate signing keys on the > >>>>> "machine" keyring need to be identified. Similar to the > >>>>> KEY_ALLOC_BUILT_IN/KEY_FLAG_BUILTIN, new flags > >>>>> KEY_ALLOC_MACHINE/KEY_FLAG_MACHINE should be defined instead. > >>>> > >>>> I’m open to renaming these, however this name change seems confusing to me. > >>>> This flag gets set when the X.509 certificate contains the three CA requirements > >>>> identified above. The remaining keys in the machine keyring can be used for > >>>> anything else. > >>> > >>> Renaming the flag to KEY_ALLOC_MACHINE/KEY_FLAG_MACHINE differentiates > >>> between the "builtin" keys from the "machine" keys. The trust models > >>> are very different. > >> > >> Isn’t the trust model the same for machine and secondary keys? Both are supplied by > >> the end-user. That is why I’m confused by naming something _MACHINE when it applies > >> to more than one keyring. > > > > True both are supplied by the end-user, but the trust models are > > different. > > I think I need more information here, I’m not seeing how they are different trust > models. In order to discuss trust models, we need to understand the different use-cases that are being discussed here without ever having been explicitly stated. Here are a few: - Allow users to sign their own kernel modules. - Allow users to selectively authorize 3rd party certificates to verify kernel modules. - From an IMA perspective, allow users to sign files within their own software packages. Each of the above use-cases needs to be independently configurable, thoroughly explained, and enforced. thanks, Mimi > > > In one case the certificates are coming indirectly from > > firmware,
> On Apr 11, 2022, at 9:30 AM, Mimi Zohar <zohar@linux.ibm.com> wrote: > > On Fri, 2022-04-08 at 21:59 +0000, Eric Snowberg wrote: >>> On Apr 8, 2022, at 12:49 PM, Mimi Zohar <zohar@linux.ibm.com> wrote: >>> >>> On Fri, 2022-04-08 at 17:34 +0000, Eric Snowberg wrote: >>>> >>>>> On Apr 8, 2022, at 10:55 AM, Mimi Zohar <zohar@linux.ibm.com> wrote: >>>>> >>>>> On Fri, 2022-04-08 at 15:27 +0000, Eric Snowberg wrote: >>>>>> >>>>>>> On Apr 8, 2022, at 8:40 AM, Mimi Zohar <zohar@linux.ibm.com> wrote: >>>>>>> >>>>>>> On Tue, 2022-04-05 at 21:53 -0400, Eric Snowberg wrote: >>>>>>>> >>>>>>>> The first type of key to use this is X.509. When a X.509 certificate >>>>>>>> is self signed, has the kernCertSign Key Usage set and contains the >>>>>>>> CA bit set this new flag is set. >>>>>>>> >>>>>>>> Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com> >>>>>>>> >>>>>>>> diff --git a/include/linux/key.h b/include/linux/key.h >>>>>>>> index 7febc4881363..97f6a1f86a27 100644 >>>>>>>> --- a/include/linux/key.h >>>>>>>> +++ b/include/linux/key.h >>>>>>>> @@ -230,6 +230,7 @@ struct key { >>>>>>>> #define KEY_FLAG_ROOT_CAN_INVAL 7 /* set if key can be invalidated by root without permission */ >>>>>>>> #define KEY_FLAG_KEEP 8 /* set if key should not be removed */ >>>>>>>> #define KEY_FLAG_UID_KEYRING 9 /* set if key is a user or user session keyring */ >>>>>>>> +#define KEY_FLAG_BUILTIN_ROT 10 /* set if key is a builtin Root of Trust key */ >>>>>>>> >>>>>>>> /* the key type and key description string >>>>>>>> * - the desc is used to match a key against search criteria >>>>>>>> @@ -290,6 +291,7 @@ extern struct key *key_alloc(struct key_type *type, >>>>>>>> #define KEY_ALLOC_BYPASS_RESTRICTION 0x0008 /* Override the check on restricted keyrings */ >>>>>>>> #define KEY_ALLOC_UID_KEYRING 0x0010 /* allocating a user or user session keyring */ >>>>>>>> #define KEY_ALLOC_SET_KEEP 0x0020 /* Set the KEEP flag on the key/keyring */ >>>>>>>> +#define KEY_ALLOC_BUILT_IN_ROT 0x0040 /* Add builtin root of trust key */ >>>>>>> >>>>>>> Since the concept of root of trust is not generic, but limited to >>>>>>> specific keyrings, the root CA certificate signing keys on the >>>>>>> "machine" keyring need to be identified. Similar to the >>>>>>> KEY_ALLOC_BUILT_IN/KEY_FLAG_BUILTIN, new flags >>>>>>> KEY_ALLOC_MACHINE/KEY_FLAG_MACHINE should be defined instead. >>>>>> >>>>>> I’m open to renaming these, however this name change seems confusing to me. >>>>>> This flag gets set when the X.509 certificate contains the three CA requirements >>>>>> identified above. The remaining keys in the machine keyring can be used for >>>>>> anything else. >>>>> >>>>> Renaming the flag to KEY_ALLOC_MACHINE/KEY_FLAG_MACHINE differentiates >>>>> between the "builtin" keys from the "machine" keys. The trust models >>>>> are very different. >>>> >>>> Isn’t the trust model the same for machine and secondary keys? Both are supplied by >>>> the end-user. That is why I’m confused by naming something _MACHINE when it applies >>>> to more than one keyring. >>> >>> True both are supplied by the end-user, but the trust models are >>> different. >> >> I think I need more information here, I’m not seeing how they are different trust >> models. > > In order to discuss trust models, we need to understand the different > use-cases that are being discussed here without ever having been > explicitly stated. Here are a few: > - Allow users to sign their own kernel modules. > - Allow users to selectively authorize 3rd party certificates to verify > kernel modules. > - From an IMA perspective, allow users to sign files within their own > software packages. > > Each of the above use-cases needs to be independently configurable, > thoroughly explained, and enforced. I’m still confused by the request here. All these use cases can be done today with insert-sys-cert. Take the, " allow user to sign their own kernel modules" use case. Using insert-sys-cert, any type of key can be added to the builtin trusted keyring, it doesn’t need to be self signed, there are no restrictions on fields in the certificate. The same approach can be used to allow users to ima sign their own files. Any key can be added, it doesn’t need to be a CA. The same goes for 3rd party signed modules. This series doesn’t enable keys to be used for any new purpose than what can be done today. In fact it limits how system keys may be used. It does this by adding a new restriction. The new restriction enforces the CA requirements ima expects. This restriction is enforced on all keyrings ima references (builtin or secondary). Since the machine keyring is linked to the secondary, it may now be used, since the CA restriction ima expects will be enforced.
On Thu, 2022-04-14 at 21:59 +0000, Eric Snowberg wrote: > > > On Apr 14, 2022, at 12:09 PM, Mimi Zohar <zohar@linux.ibm.com> wrote: > > > > On Thu, 2022-04-14 at 16:36 +0000, Eric Snowberg wrote: > >> > >>> On Apr 11, 2022, at 9:30 AM, Mimi Zohar <zohar@linux.ibm.com> wrote: > >>> > >>> On Fri, 2022-04-08 at 21:59 +0000, Eric Snowberg wrote: > >>>>> On Apr 8, 2022, at 12:49 PM, Mimi Zohar <zohar@linux.ibm.com> wrote: > >>>>> > >>>>> On Fri, 2022-04-08 at 17:34 +0000, Eric Snowberg wrote: > >>>>>> > >>>>>>> On Apr 8, 2022, at 10:55 AM, Mimi Zohar <zohar@linux.ibm.com> wrote: > >>>>>>> > >>>>>>> On Fri, 2022-04-08 at 15:27 +0000, Eric Snowberg wrote: > >>>>>>>> > >>>>>>>>> On Apr 8, 2022, at 8:40 AM, Mimi Zohar <zohar@linux.ibm.com> wrote: > >>>>>>>>> > >>>>>>>>> On Tue, 2022-04-05 at 21:53 -0400, Eric Snowberg wrote: > >>>>>>>>>> > >>>>>>>>>> The first type of key to use this is X.509. When a X.509 certificate > >>>>>>>>>> is self signed, has the kernCertSign Key Usage set and contains the > >>>>>>>>>> CA bit set this new flag is set. > >>>>>>>>>> > >>>>>>>>>> Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com> > >>>>>>>>>> > >>>>>>>>>> diff --git a/include/linux/key.h b/include/linux/key.h > >>>>>>>>>> index 7febc4881363..97f6a1f86a27 100644 > >>>>>>>>>> --- a/include/linux/key.h > >>>>>>>>>> +++ b/include/linux/key.h > >>>>>>>>>> @@ -230,6 +230,7 @@ struct key { > >>>>>>>>>> #define KEY_FLAG_ROOT_CAN_INVAL 7 /* set if key can be invalidated by root without permission */ > >>>>>>>>>> #define KEY_FLAG_KEEP 8 /* set if key should not be removed */ > >>>>>>>>>> #define KEY_FLAG_UID_KEYRING 9 /* set if key is a user or user session keyring */ > >>>>>>>>>> +#define KEY_FLAG_BUILTIN_ROT 10 /* set if key is a builtin Root of Trust key */ > >>>>>>>>>> > >>>>>>>>>> /* the key type and key description string > >>>>>>>>>> * - the desc is used to match a key against search criteria > >>>>>>>>>> @@ -290,6 +291,7 @@ extern struct key *key_alloc(struct key_type *type, > >>>>>>>>>> #define KEY_ALLOC_BYPASS_RESTRICTION 0x0008 /* Override the check on restricted keyrings */ > >>>>>>>>>> #define KEY_ALLOC_UID_KEYRING 0x0010 /* allocating a user or user session keyring */ > >>>>>>>>>> #define KEY_ALLOC_SET_KEEP 0x0020 /* Set the KEEP flag on the key/keyring */ > >>>>>>>>>> +#define KEY_ALLOC_BUILT_IN_ROT 0x0040 /* Add builtin root of trust key */ > >>>>>>>>> > >>>>>>>>> Since the concept of root of trust is not generic, but limited to > >>>>>>>>> specific keyrings, the root CA certificate signing keys on the > >>>>>>>>> "machine" keyring need to be identified. Similar to the > >>>>>>>>> KEY_ALLOC_BUILT_IN/KEY_FLAG_BUILTIN, new flags > >>>>>>>>> KEY_ALLOC_MACHINE/KEY_FLAG_MACHINE should be defined instead. > >>>>>>>> > >>>>>>>> I’m open to renaming these, however this name change seems confusing to me. > >>>>>>>> This flag gets set when the X.509 certificate contains the three CA requirements > >>>>>>>> identified above. The remaining keys in the machine keyring can be used for > >>>>>>>> anything else. > >>>>>>> > >>>>>>> Renaming the flag to KEY_ALLOC_MACHINE/KEY_FLAG_MACHINE differentiates > >>>>>>> between the "builtin" keys from the "machine" keys. The trust models > >>>>>>> are very different. > >>>>>> > >>>>>> Isn’t the trust model the same for machine and secondary keys? Both are supplied by > >>>>>> the end-user. That is why I’m confused by naming something _MACHINE when it applies > >>>>>> to more than one keyring. > >>>>> > >>>>> True both are supplied by the end-user, but the trust models are > >>>>> different. > >>>> > >>>> I think I need more information here, I’m not seeing how they are different trust > >>>> models. > >>> > >>> In order to discuss trust models, we need to understand the different > >>> use-cases that are being discussed here without ever having been > >>> explicitly stated. Here are a few: > >>> - Allow users to sign their own kernel modules. > >>> - Allow users to selectively authorize 3rd party certificates to verify > >>> kernel modules. > >>> - From an IMA perspective, allow users to sign files within their own > >>> software packages. > >>> > >>> Each of the above use-cases needs to be independently configurable, > >>> thoroughly explained, and enforced. > >> > >> I’m still confused by the request here. All these use cases can be done > >> today with insert-sys-cert. Take the, " allow user to sign their own kernel > >> modules" use case. Using insert-sys-cert, any type of key can be added > >> to the builtin trusted keyring, it doesn’t need to be self signed, there are > >> no restrictions on fields in the certificate. The same approach can be used > >> to allow users to ima sign their own files. Any key can be added, it doesn’t > >> need to be a CA. The same goes for 3rd party signed modules. > > > > The difference is "where" the key is coming from. In the builtin use- > > case or the post build insert-sys-cert case, the kernel image is > > signed, or re-signed, and the kernel image signature is verified. The > > root of trust is straight forward - secure boot with a HW root of trust > > up to and including verifying the kernel image signature, then > > transition to the builtin keys. > > > > Keys on the "machine" keyring are not part of that signature chain of > > trust, > > The machine keyring contains all keys in the MokList. On x86 (and other > architectures that boot with shim) all keys in the MokList are part of the signature > chain of trust. Shim uses MOKList keys to validate the kernel image signature > when booting with SecureBoot enabled. Secure Boot DB keys are used to > validate shim, but rarely used to validate the kernel. Sure, keys on the "machine" keyring can be used to verify the kexec kernel image signature. As all of the above requirements is satisfied by loading a root CA, def ined as a KeySigning cert, without needing to load all of the MOK keys onto the "machine" keyring, support both trust models. Please make loading all MOK keys configurable, with a thorough explanation. thanks, Mimi
diff --git a/crypto/asymmetric_keys/x509_public_key.c b/crypto/asymmetric_keys/x509_public_key.c index 91a4ad50dea2..7290e765f46b 100644 --- a/crypto/asymmetric_keys/x509_public_key.c +++ b/crypto/asymmetric_keys/x509_public_key.c @@ -215,6 +215,8 @@ static int x509_key_preparse(struct key_preparsed_payload *prep) prep->payload.data[asym_auth] = cert->sig; prep->description = desc; prep->quotalen = 100; + if (cert->is_kcs_set && cert->self_signed && cert->is_root_ca) + prep->payload_flags |= KEY_ALLOC_ROT; /* We've finished with the certificate */ cert->pub = NULL; diff --git a/include/linux/key-type.h b/include/linux/key-type.h index 7d985a1dfe4a..ed0aaad3849b 100644 --- a/include/linux/key-type.h +++ b/include/linux/key-type.h @@ -36,6 +36,8 @@ struct key_preparsed_payload { size_t datalen; /* Raw datalen */ size_t quotalen; /* Quota length for proposed payload */ time64_t expiry; /* Expiry time of key */ + unsigned int payload_flags; /* Proposed payload flags */ +#define KEY_ALLOC_ROT 0x0001 /* Proposed Root of Trust (ROT) key */ } __randomize_layout; typedef int (*request_key_actor_t)(struct key *auth_key, void *aux); diff --git a/include/linux/key.h b/include/linux/key.h index 7febc4881363..97f6a1f86a27 100644 --- a/include/linux/key.h +++ b/include/linux/key.h @@ -230,6 +230,7 @@ struct key { #define KEY_FLAG_ROOT_CAN_INVAL 7 /* set if key can be invalidated by root without permission */ #define KEY_FLAG_KEEP 8 /* set if key should not be removed */ #define KEY_FLAG_UID_KEYRING 9 /* set if key is a user or user session keyring */ +#define KEY_FLAG_BUILTIN_ROT 10 /* set if key is a builtin Root of Trust key */ /* the key type and key description string * - the desc is used to match a key against search criteria @@ -290,6 +291,7 @@ extern struct key *key_alloc(struct key_type *type, #define KEY_ALLOC_BYPASS_RESTRICTION 0x0008 /* Override the check on restricted keyrings */ #define KEY_ALLOC_UID_KEYRING 0x0010 /* allocating a user or user session keyring */ #define KEY_ALLOC_SET_KEEP 0x0020 /* Set the KEEP flag on the key/keyring */ +#define KEY_ALLOC_BUILT_IN_ROT 0x0040 /* Add builtin root of trust key */ extern void key_revoke(struct key *key); extern void key_invalidate(struct key *key); diff --git a/security/keys/key.c b/security/keys/key.c index c45afdd1dfbb..732bb837fc51 100644 --- a/security/keys/key.c +++ b/security/keys/key.c @@ -305,6 +305,8 @@ struct key *key_alloc(struct key_type *type, const char *desc, key->flags |= 1 << KEY_FLAG_UID_KEYRING; if (flags & KEY_ALLOC_SET_KEEP) key->flags |= 1 << KEY_FLAG_KEEP; + if (flags & KEY_ALLOC_BUILT_IN_ROT) + key->flags |= 1 << KEY_FLAG_BUILTIN_ROT; #ifdef KEY_DEBUGGING key->magic = KEY_DEBUG_MAGIC; @@ -929,6 +931,12 @@ key_ref_t key_create_or_update(key_ref_t keyring_ref, perm |= KEY_POS_WRITE; } + /* Only allow KEY_ALLOC_BUILT_IN_ROT flag to be set by preparser contents */ + if (prep.payload_flags & KEY_ALLOC_ROT) + flags |= KEY_ALLOC_BUILT_IN_ROT; + else + flags &= ~KEY_ALLOC_BUILT_IN_ROT; + /* allocate a new key */ key = key_alloc(index_key.type, index_key.description, cred->fsuid, cred->fsgid, cred, perm, flags, NULL);
Some subsystems are interested in knowing if keys within a keyring could be used as a foundation of a root of trust. Introduce a new builtin root of trust key flag. The first type of key to use this is X.509. When a X.509 certificate is self signed, has the kernCertSign Key Usage set and contains the CA bit set this new flag is set. Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com> --- crypto/asymmetric_keys/x509_public_key.c | 2 ++ include/linux/key-type.h | 2 ++ include/linux/key.h | 2 ++ security/keys/key.c | 8 ++++++++ 4 files changed, 14 insertions(+)