8a4e1fcd4b
Upstream commit 6471384af2a6530696fc0203bafe4de41a23c9ef. 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 CONFIG_INIT_ON_FREE_DEFAULT_ON. 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.com Signed-off-by: Alexander Potapenko <glider@google.com> Acked-by: Kees 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: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Removed the drivers/infiniband/core/uverbs_ioctl.c part, which is not in android-common 4.14 kernel. Change-Id: I6b5482fcafae89615e1d79879191fb6ce50d56cf Bug: 138435492 Test: Boot cuttlefish with and without Test: CONFIG_INIT_ON_ALLOC_DEFAULT_ON/CONFIG_INIT_ON_FREE_DEFAULT_ON Test: Boot an ARM64 mobile device with and without Test: CONFIG_INIT_ON_ALLOC_DEFAULT_ON/CONFIG_INIT_ON_FREE_DEFAULT_ON Signed-off-by: Alexander Potapenko <glider@google.com>
71 lines
2.7 KiB
Plaintext
71 lines
2.7 KiB
Plaintext
menu "Kernel hardening options"
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menu "Memory initialization"
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choice
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prompt "Initialize kernel stack variables at function entry"
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default INIT_STACK_NONE
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help
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This option enables initialization of stack variables at
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function entry time. This has the possibility to have the
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greatest coverage (since all functions can have their
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variables initialized), but the performance impact depends
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on the function calling complexity of a given workload's
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syscalls.
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This chooses the level of coverage over classes of potentially
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uninitialized variables. The selected class will be
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initialized before use in a function.
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config INIT_STACK_NONE
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bool "no automatic initialization (weakest)"
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help
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Disable automatic stack variable initialization.
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This leaves the kernel vulnerable to the standard
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classes of uninitialized stack variable exploits
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and information exposures.
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config INIT_STACK_ALL
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bool "0xAA-init everything on the stack (strongest)"
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help
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Initializes everything on the stack with a 0xAA
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pattern. This is intended to eliminate all classes
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of uninitialized stack variable exploits and information
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exposures, even variables that were warned to have been
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left uninitialized.
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endchoice
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config INIT_ON_ALLOC_DEFAULT_ON
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bool "Enable heap memory zeroing on allocation by default"
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help
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This has the effect of setting "init_on_alloc=1" on the kernel
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command line. This can be disabled with "init_on_alloc=0".
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When "init_on_alloc" is enabled, all page allocator and slab
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allocator memory will be zeroed when allocated, eliminating
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many kinds of "uninitialized heap memory" flaws, especially
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heap content exposures. The performance impact varies by
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workload, but most cases see <1% impact. Some synthetic
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workloads have measured as high as 7%.
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config INIT_ON_FREE_DEFAULT_ON
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bool "Enable heap memory zeroing on free by default"
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help
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This has the effect of setting "init_on_free=1" on the kernel
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command line. This can be disabled with "init_on_free=0".
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Similar to "init_on_alloc", when "init_on_free" is enabled,
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all page allocator and slab allocator memory will be zeroed
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when freed, eliminating many kinds of "uninitialized heap memory"
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flaws, especially heap content exposures. The primary difference
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with "init_on_free" is that data lifetime in memory is reduced,
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as anything freed is wiped immediately, making live forensics or
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cold boot memory attacks unable to recover freed memory contents.
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The performance impact varies by workload, but is more expensive
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than "init_on_alloc" due to the negative cache effects of
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touching "cold" memory areas. Most cases see 3-5% impact. Some
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synthetic workloads have measured as high as 8%.
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endmenu
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endmenu
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