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    Subject[PATCH v9 0/9] mm: introduce memfd_secret system call to create "secret" memory areas
    Date
    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.

    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.

    v9:
    * Fix build with and without CONFIG_MEMCG
    * Update memcg accounting to avoid copying memcg_data, per Roman comments
    * Fix issues in secretmem_fault(), thanks Matthew
    * Do not wire up syscall in arm64 compatibility layer

    v8: https://lore.kernel.org/lkml/20201110151444.20662-1-rppt@kernel.org
    * 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@kernel.org
    * 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 (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 | 3 +-
    mm/gup.c | 10 +
    mm/internal.h | 3 +
    mm/mmap.c | 5 +-
    mm/secretmem.c | 446 ++++++++++++++++++++++
    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, 891 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

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