• Alexander Potapenko's avatar
    mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options · 6471384a
    Alexander Potapenko authored
    Patch series "add init_on_alloc/init_on_free boot options", v10.
    Provide init_on_alloc and init_on_free boot options.
    These are aimed at preventing possible information leaks and making the
    control-flow bugs that depend on uninitialized values more deterministic.
    Enabling either of the options guarantees that the memory returned by the
    page allocator and SL[AU]B is initialized with zeroes.  SLOB allocator
    isn't supported at the moment, as its emulation of kmem caches complicates
    handling of SLAB_TYPESAFE_BY_RCU caches correctly.
    Enabling init_on_free also guarantees that pages and heap objects are
    initialized right after they're freed, so it won't be possible to access
    stale data by using a dangling pointer.
    As suggested by Michal Hocko, right now we don't let the heap users to
    disable initialization for certain allocations.  There's not enough
    evidence that doing so can speed up real-life cases, and introducing ways
    to opt-out may result in things going out of control.
    This patch (of 2):
    The new options are needed to prevent possible information leaks and make
    control-flow bugs that depend on uninitialized values more deterministic.
    This is expected to be on-by-default on Android and Chrome OS.  And it
    gives the opportunity for anyone else to use it under distros too via the
    boot args.  (The init_on_free feature is regularly requested by folks
    where memory forensics is included in their threat models.)
    init_on_alloc=1 makes the kernel initialize newly allocated pages and heap
    objects with zeroes.  Initialization is done at allocation time at the
    places where checks for __GFP_ZERO are performed.
    init_on_free=1 makes the kernel initialize freed pages and heap objects
    with zeroes upon their deletion.  This helps to ensure sensitive data
    doesn't leak via use-after-free accesses.
    Both init_on_alloc=1 and init_on_free=1 guarantee that the allocator
    returns zeroed memory.  The two exceptions are slab caches with
    constructors and SLAB_TYPESAFE_BY_RCU flag.  Those are never
    zero-initialized to preserve their semantics.
    Both init_on_alloc and init_on_free default to zero, but those defaults
    can be overridden with CONFIG_INIT_ON_ALLOC_DEFAULT_ON and
    If either SLUB poisoning or page poisoning is enabled, those options take
    precedence over init_on_alloc and init_on_free: initialization is only
    applied to unpoisoned allocations.
    Slowdown for the new features compared to init_on_free=0, init_on_alloc=0:
    hackbench, init_on_free=1:  +7.62% sys time (st.err 0.74%)
    hackbench, init_on_alloc=1: +7.75% sys time (st.err 2.14%)
    Linux build with -j12, init_on_free=1:  +8.38% wall time (st.err 0.39%)
    Linux build with -j12, init_on_free=1:  +24.42% sys time (st.err 0.52%)
    Linux build with -j12, init_on_alloc=1: -0.13% wall time (st.err 0.42%)
    Linux build with -j12, init_on_alloc=1: +0.57% sys time (st.err 0.40%)
    The slowdown for init_on_free=0, init_on_alloc=0 compared to the baseline
    is within the standard error.
    The new features are also going to pave the way for hardware memory
    tagging (e.g.  arm64's MTE), which will require both on_alloc and on_free
    hooks to set the tags for heap objects.  With MTE, tagging will have the
    same cost as memory initialization.
    Although init_on_free is rather costly, there are paranoid use-cases where
    in-memory data lifetime is desired to be minimized.  There are various
    arguments for/against the realism of the associated threat models, but
    given that we'll need the infrastructure for MTE anyway, and there are
    people who want wipe-on-free behavior no matter what the performance cost,
    it seems reasonable to include it in this series.
    [glider@google.com: v8]
      Link: http://lkml.kernel.org/r/20190626121943.131390-2-glider@google.com
    [glider@google.com: v9]
      Link: http://lkml.kernel.org/r/20190627130316.254309-2-glider@google.com
    [glider@google.com: v10]
      Link: http://lkml.kernel.org/r/20190628093131.199499-2-glider@google.com
    Link: http://lkml.kernel.org/r/20190617151050.92663-2-glider@google.comSigned-off-by: default avatarAlexander Potapenko <glider@google.com>
    Acked-by: default avatarKees Cook <keescook@chromium.org>
    Acked-by: Michal Hocko <mhocko@suse.cz>		[page and dmapool parts
    Acked-by: James Morris <jamorris@linux.microsoft.com>]
    Cc: Christoph Lameter <cl@linux.com>
    Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
    Cc: "Serge E. Hallyn" <serge@hallyn.com>
    Cc: Nick Desaulniers <ndesaulniers@google.com>
    Cc: Kostya Serebryany <kcc@google.com>
    Cc: Dmitry Vyukov <dvyukov@google.com>
    Cc: Sandeep Patil <sspatil@android.com>
    Cc: Laura Abbott <labbott@redhat.com>
    Cc: Randy Dunlap <rdunlap@infradead.org>
    Cc: Jann Horn <jannh@google.com>
    Cc: Mark Rutland <mark.rutland@arm.com>
    Cc: Marco Elver <elver@google.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
dmapool.c 13.8 KB