| Message ID | 20201026083752.13267-1-rppt@kernel.org |
|---|---|
| Headers | show |
| Series | mm: introduce memfd_secret system call to create "secret" memory areas | expand |
On Mon, 2020-10-26 at 10:37 +0200, Mike Rapoport wrote: > +++ b/arch/x86/mm/pat/set_memory.c > @@ -2184,14 +2184,14 @@ static int __set_pages_np(struct page *page, > int numpages) > return __change_page_attr_set_clr(&cpa, 0); > } > > -int set_direct_map_invalid_noflush(struct page *page) > +int set_direct_map_invalid_noflush(struct page *page, int numpages) > { > - return __set_pages_np(page, 1); > + return __set_pages_np(page, numpages); > } > > -int set_direct_map_default_noflush(struct page *page) > +int set_direct_map_default_noflush(struct page *page, int numpages) > { > - return __set_pages_p(page, 1); > + return __set_pages_p(page, numpages); > } Somewhat related to your other series, this could result in large NP pages and trip up hibernate.
On 26.10.20 20:01, Edgecombe, Rick P wrote: > On Mon, 2020-10-26 at 10:37 +0200, Mike Rapoport wrote: >> +++ b/arch/x86/mm/pat/set_memory.c >> @@ -2184,14 +2184,14 @@ static int __set_pages_np(struct page *page, >> int numpages) >> return __change_page_attr_set_clr(&cpa, 0); >> } >> >> -int set_direct_map_invalid_noflush(struct page *page) >> +int set_direct_map_invalid_noflush(struct page *page, int numpages) >> { >> - return __set_pages_np(page, 1); >> + return __set_pages_np(page, numpages); >> } >> >> -int set_direct_map_default_noflush(struct page *page) >> +int set_direct_map_default_noflush(struct page *page, int numpages) >> { >> - return __set_pages_p(page, 1); >> + return __set_pages_p(page, numpages); >> } > > Somewhat related to your other series, this could result in large NP > pages and trip up hibernate. > It feels somewhat desirable to disable hibernation once secretmem is enabled, right? Otherwise you'll be writing out your secrets to swap, where they will remain even after booting up again ... Skipping secretmem pages when hibernating is the wrong approach I guess ...
On 26.10.20 09:37, Mike Rapoport wrote: > From: Mike Rapoport <rppt@linux.ibm.com> > > The definition of PMD_PAGE_ORDER denoting the number of base pages in the > second-level leaf page is already used by DAX and maybe handy in other > cases as well. > > Several architectures already have definition of PMD_ORDER as the size of > second level page table, so to avoid conflict with these definitions use > PMD_PAGE_ORDER name and update DAX respectively. > > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> Reviewed-by: David Hildenbrand <david@redhat.com>
On Tue, Oct 27, 2020 at 09:12:23AM +0100, David Hildenbrand wrote: > On 26.10.20 20:01, Edgecombe, Rick P wrote: > > On Mon, 2020-10-26 at 10:37 +0200, Mike Rapoport wrote: > >> +++ b/arch/x86/mm/pat/set_memory.c > >> @@ -2184,14 +2184,14 @@ static int __set_pages_np(struct page *page, > >> int numpages) > >> return __change_page_attr_set_clr(&cpa, 0); > >> } > >> > >> -int set_direct_map_invalid_noflush(struct page *page) > >> +int set_direct_map_invalid_noflush(struct page *page, int numpages) > >> { > >> - return __set_pages_np(page, 1); > >> + return __set_pages_np(page, numpages); > >> } > >> > >> -int set_direct_map_default_noflush(struct page *page) > >> +int set_direct_map_default_noflush(struct page *page, int numpages) > >> { > >> - return __set_pages_p(page, 1); > >> + return __set_pages_p(page, numpages); > >> } > > > > Somewhat related to your other series, this could result in large NP > > pages and trip up hibernate. > > > > It feels somewhat desirable to disable hibernation once secretmem is > enabled, right? Otherwise you'll be writing out your secrets to swap, > where they will remain even after booting up again ... > > Skipping secretmem pages when hibernating is the wrong approach I guess ... Completely agree. I'll look into preventing hibernation from touching secretmem. > -- > Thanks, > > David / dhildenb >
From: Mike Rapoport <rppt@linux.ibm.com> Hi, This is an implementation of "secret" mappings backed by a file descriptor. The file descriptor backing secret memory mappings is created using a dedicated memfd_secret system call The desired protection mode for the memory is configured using flags parameter of the system call. The mmap() of the file descriptor created with memfd_secret() will create a "secret" memory mapping. The pages in that mapping will be marked as not present in the direct map and will have desired protection bits set in the user page table. For instance, current implementation allows uncached mappings. Although normally Linux userspace mappings are protected from other users, such secret mappings are useful for environments where a hostile tenant is trying to trick the kernel into giving them access to other tenants mappings. Additionally, in the future the secret mappings may be used as a mean to protect guest memory in a virtual machine host. For demonstration of secret memory usage we've created a userspace library https://git.kernel.org/pub/scm/linux/kernel/git/jejb/secret-memory-preloader.git that does two things: the first is act as a preloader for openssl to redirect all the OPENSSL_malloc calls to secret memory meaning any secret keys get automatically protected this way and the other thing it does is expose the API to the user who needs it. We anticipate that a lot of the use cases would be like the openssl one: many toolkits that deal with secret keys already have special handling for the memory to try to give them greater protection, so this would simply be pluggable into the toolkits without any need for user application modification. Hiding secret memory mappings behind an anonymous file allows (ab)use of the page cache for tracking pages allocated for the "secret" mappings as well as using address_space_operations for e.g. page migration callbacks. The anonymous file may be also used implicitly, like hugetlb files, to implement mmap(MAP_SECRET) and use the secret memory areas with "native" mm ABIs in the future. To limit fragmentation of the direct map to splitting only PUD-size pages, I've added an amortizing cache of PMD-size pages to each file descriptor that is used as an allocation pool for the secret memory areas. It is easy to add boot time reservation of the memory for secretmem needs. There was an implementation in earlier version of this set, but I've dropped it for now as there is no consensus whether the boot time reservation should be done from memblock or from CMA. I beleive we can have this discussion after straightening out the basic implementation. v7: * Use set_direct_map() instead of __kernel_map_pages() to ensure error handling in case the direct map update fails * Add accounting of large pages used to reduce the direct map fragmentation * Teach get_user_pages() and frieds to refuse get/pin secretmem pages v6: https://lore.kernel.org/lkml/20200924132904.1391-1-rppt@kernel.org * Silence the warning about missing syscall, thanks to Qian Cai * Replace spaces with tabs in Kconfig additions, per Randy * Add a selftest. v5: https://lore.kernel.org/lkml/20200916073539.3552-1-rppt@kernel.org * rebase on v5.9-rc5 * drop boot time memory reservation patch v4: https://lore.kernel.org/lkml/20200818141554.13945-1-rppt@kernel.org * rebase on v5.9-rc1 * Do not redefine PMD_PAGE_ORDER in fs/dax.c, thanks Kirill * Make secret mappings exclusive by default and only require flags to memfd_secret() system call for uncached mappings, thanks again Kirill :) v3: https://lore.kernel.org/lkml/20200804095035.18778-1-rppt@kernel.org * Squash kernel-parameters.txt update into the commit that added the command line option. * Make uncached mode explicitly selectable by architectures. For now enable it only on x86. v2: https://lore.kernel.org/lkml/20200727162935.31714-1-rppt@kernel.org * Follow Michael's suggestion and name the new system call 'memfd_secret' * Add kernel-parameters documentation about the boot option * Fix i386-tinyconfig regression reported by the kbuild bot. CONFIG_SECRETMEM now depends on !EMBEDDED to disable it on small systems from one side and still make it available unconditionally on architectures that support SET_DIRECT_MAP. v1: https://lore.kernel.org/lkml/20200720092435.17469-1-rppt@kernel.org Mike Rapoport (8): mm: add definition of PMD_PAGE_ORDER mmap: make mlock_future_check() global set_memory: allow set_direct_map_*_noflush() for multiple pages mm: introduce memfd_secret system call to create "secret" memory areas arch, mm: wire up memfd_secret system call were relevant mm: secretmem: use PMD-size pages to amortize direct map fragmentation secretmem: test: add basic selftest for memfd_secret(2) mm: secretmem: add ability to reserve memory at boot arch/Kconfig | 7 + arch/arm64/include/asm/cacheflush.h | 4 +- arch/arm64/include/asm/unistd.h | 2 +- arch/arm64/include/asm/unistd32.h | 2 + arch/arm64/include/uapi/asm/unistd.h | 1 + arch/arm64/mm/pageattr.c | 10 +- arch/riscv/include/asm/set_memory.h | 4 +- arch/riscv/include/asm/unistd.h | 1 + arch/riscv/mm/pageattr.c | 8 +- arch/x86/Kconfig | 1 + arch/x86/entry/syscalls/syscall_32.tbl | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + arch/x86/include/asm/set_memory.h | 4 +- arch/x86/mm/pat/set_memory.c | 8 +- fs/dax.c | 11 +- include/linux/pgtable.h | 3 + include/linux/set_memory.h | 4 +- include/linux/syscalls.h | 1 + include/uapi/asm-generic/unistd.h | 7 +- include/uapi/linux/magic.h | 1 + include/uapi/linux/secretmem.h | 8 + kernel/sys_ni.c | 2 + mm/Kconfig | 4 + mm/Makefile | 1 + mm/gup.c | 10 + mm/internal.h | 3 + mm/mmap.c | 5 +- mm/secretmem.c | 487 ++++++++++++++++++++++ mm/vmalloc.c | 5 +- scripts/checksyscalls.sh | 4 + tools/testing/selftests/vm/.gitignore | 1 + tools/testing/selftests/vm/Makefile | 3 +- tools/testing/selftests/vm/memfd_secret.c | 296 +++++++++++++ tools/testing/selftests/vm/run_vmtests | 17 + 34 files changed, 892 insertions(+), 35 deletions(-) create mode 100644 include/uapi/linux/secretmem.h create mode 100644 mm/secretmem.c create mode 100644 tools/testing/selftests/vm/memfd_secret.c -- 2.28.0