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    Subject[PATCH v14 00/10] mm: introduce memfd_secret system call to create "secret" memory areas
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    From: Mike Rapoport <rppt@linux.ibm.com>

    Hi,

    @Andrew, this is based on v5.10-rc2-mmotm-2020-11-07-21-40, I can rebase on
    current mmotm if you prefer.

    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 be present only in the page table of the owning mm.

    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.

    v14:
    * Finally s/mod_node_page_state/mod_lruvec_page_state/

    v13: https://lore.kernel.org/lkml/20201201074559.27742-1-rppt@kernel.org
    * Added Reviewed-by, thanks Catalin and David
    * s/mod_node_page_state/mod_lruvec_page_state/ as Shakeel suggested

    v12: https://lore.kernel.org/lkml/20201125092208.12544-1-rppt@kernel.org
    * Add detection of whether set_direct_map has actual effect on arm64 and bail
    out of CMA allocation for secretmem and the memfd_secret() syscall if pages
    would not be removed from the direct map

    v11: https://lore.kernel.org/lkml/20201124092556.12009-1-rppt@kernel.org
    * Drop support for uncached mappings

    v10: https://lore.kernel.org/lkml/20201123095432.5860-1-rppt@kernel.org
    * Drop changes to arm64 compatibility layer
    * Add Roman's Ack for memcg accounting

    Older history:
    v9: https://lore.kernel.org/lkml/20201117162932.13649-1-rppt@kernel.org
    v8: https://lore.kernel.org/lkml/20201110151444.20662-1-rppt@kernel.org
    v7: https://lore.kernel.org/lkml/20201026083752.13267-1-rppt@kernel.org
    v6: https://lore.kernel.org/lkml/20200924132904.1391-1-rppt@kernel.org
    v5: https://lore.kernel.org/lkml/20200916073539.3552-1-rppt@kernel.org
    v4: https://lore.kernel.org/lkml/20200818141554.13945-1-rppt@kernel.org
    v3: https://lore.kernel.org/lkml/20200804095035.18778-1-rppt@kernel.org
    v2: https://lore.kernel.org/lkml/20200727162935.31714-1-rppt@kernel.org
    v1: https://lore.kernel.org/lkml/20200720092435.17469-1-rppt@kernel.org

    Mike Rapoport (10):
    mm: add definition of PMD_PAGE_ORDER
    mmap: make mlock_future_check() global
    set_memory: allow set_direct_map_*_noflush() for multiple pages
    set_memory: allow querying whether set_direct_map_*() is actually enabled
    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/arm64/include/asm/Kbuild | 1 -
    arch/arm64/include/asm/cacheflush.h | 6 -
    arch/arm64/include/asm/set_memory.h | 17 +
    arch/arm64/include/uapi/asm/unistd.h | 1 +
    arch/arm64/kernel/machine_kexec.c | 1 +
    arch/arm64/mm/mmu.c | 6 +-
    arch/arm64/mm/pageattr.c | 23 +-
    arch/riscv/include/asm/set_memory.h | 4 +-
    arch/riscv/include/asm/unistd.h | 1 +
    arch/riscv/mm/pageattr.c | 8 +-
    arch/x86/Kconfig | 2 +-
    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 | 16 +-
    include/linux/syscalls.h | 1 +
    include/uapi/asm-generic/unistd.h | 6 +-
    include/uapi/linux/magic.h | 1 +
    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 | 439 ++++++++++++++++++++++
    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, 906 insertions(+), 51 deletions(-)
    create mode 100644 arch/arm64/include/asm/set_memory.h
    create mode 100644 include/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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