Hi Andrew, It'll be great if this can be pulled back to mmotm for wider exposure to testing and fuzzing. On Tue, Nov 10, 2020 at 05:14:35PM +0200, Mike Rapoport wrote: > From: Mike Rapoport <rppt@xxxxxxxxxxxxx> > > 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. > > As the memory allocated by secretmem becomes unmovable, we use CMA to back > large page caches so that page allocator won't be surprised by failing attempt > to migrate these pages. > > v8: > * Use CMA for all secretmem allocations as David suggested > * Update memcg accounting after transtion to CMA > * Prevent hibernation when there are active secretmem users > * Add zeroing of the memory before releasing it back to cma/page allocator > * Rebase on v5.10-rc2-mmotm-2020-11-07-21-40 > > v7: https://lore.kernel.org/lkml/20201026083752.13267-1-rppt@xxxxxxxxxx > * 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@xxxxxxxxxx > * 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@xxxxxxxxxx > * rebase on v5.9-rc5 > * drop boot time memory reservation patch > > v4: https://lore.kernel.org/lkml/20200818141554.13945-1-rppt@xxxxxxxxxx > * 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@xxxxxxxxxx > * 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@xxxxxxxxxx > * 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@xxxxxxxxxx > > Mike Rapoport (9): > 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 > secretmem: use PMD-size pages to amortize direct map fragmentation > secretmem: add memcg accounting > PM: hibernate: disable when there are active secretmem users > arch, mm: wire up memfd_secret system call were relevant > secretmem: test: add basic selftest for memfd_secret(2) > > 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/secretmem.h | 30 ++ > include/linux/set_memory.h | 4 +- > include/linux/syscalls.h | 1 + > include/uapi/asm-generic/unistd.h | 6 +- > include/uapi/linux/magic.h | 1 + > include/uapi/linux/secretmem.h | 8 + > kernel/power/hibernate.c | 5 +- > kernel/power/snapshot.c | 4 +- > kernel/sys_ni.c | 2 + > mm/Kconfig | 5 + > mm/Makefile | 1 + > mm/filemap.c | 2 +- > mm/gup.c | 10 + > mm/internal.h | 3 + > mm/mmap.c | 5 +- > mm/secretmem.c | 451 ++++++++++++++++++++++ > 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 | 298 ++++++++++++++ > tools/testing/selftests/vm/run_vmtests | 17 + > 38 files changed, 895 insertions(+), 39 deletions(-) > create mode 100644 include/linux/secretmem.h > create mode 100644 include/uapi/linux/secretmem.h > create mode 100644 mm/secretmem.c > create mode 100644 tools/testing/selftests/vm/memfd_secret.c > > > base-commit: 9f8ce377d420db12b19d6a4f636fecbd88a725a5 > -- > 2.28.0 > -- Sincerely yours, Mike.
