forked from Minki/linux
afba7e6c5f
8 Commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
glider@google.com
|
f0fe00d497 |
security: allow using Clang's zero initialization for stack variables
In addition to -ftrivial-auto-var-init=pattern (used by CONFIG_INIT_STACK_ALL now) Clang also supports zero initialization for locals enabled by -ftrivial-auto-var-init=zero. The future of this flag is still being debated (see https://bugs.llvm.org/show_bug.cgi?id=45497). Right now it is guarded by another flag, -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang, which means it may not be supported by future Clang releases. Another possible resolution is that -ftrivial-auto-var-init=zero will persist (as certain users have already started depending on it), but the name of the guard flag will change. In the meantime, zero initialization has proven itself as a good production mitigation measure against uninitialized locals. Unlike pattern initialization, which has a higher chance of triggering existing bugs, zero initialization provides safe defaults for strings, pointers, indexes, and sizes. On the other hand, pattern initialization remains safer for return values. Chrome OS and Android are moving to using zero initialization for production builds. Performance-wise, the difference between pattern and zero initialization is usually negligible, although the generated code for zero initialization is more compact. This patch renames CONFIG_INIT_STACK_ALL to CONFIG_INIT_STACK_ALL_PATTERN and introduces another config option, CONFIG_INIT_STACK_ALL_ZERO, that enables zero initialization for locals if the corresponding flags are supported by Clang. Cc: Kees Cook <keescook@chromium.org> Cc: Nick Desaulniers <ndesaulniers@google.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Alexander Potapenko <glider@google.com> Link: https://lore.kernel.org/r/20200616083435.223038-1-glider@google.com Reviewed-by: Maciej Żenczykowski <maze@google.com> Signed-off-by: Kees Cook <keescook@chromium.org> |
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Linus Torvalds
|
c622fc5f54 |
meminit fix
- Disable gcc-based stack variable auto-init under KASAN (Arnd Bergmann) -----BEGIN PGP SIGNATURE----- Comment: Kees Cook <kees@outflux.net> iQJKBAABCgA0FiEEpcP2jyKd1g9yPm4TiXL039xtwCYFAl099MsWHGtlZXNjb29r QGNocm9taXVtLm9yZwAKCRCJcvTf3G3AJr6GD/0Xl/YxeXPnKIHoafoqMCBAY12f OnRZ2N6YCikYfLwgBnTAAyQi3P0qU8ffjt4LjoPxzByUPBmZ+VkUBXU1eNUuU0mT 4CX+ZakeWp5atbg7Ja7DAThBrJS4DYRzXiGB1Is8IACD/zkkRDoGU1tN+3nubtlk F2SYtmJBz/6pje2ksLDmuSS1sapaom7Cs4khB/oDb8HOsqydS0CpzN7Oa/Di3HoZ yUbyM3bcgmYECasGt7zVOLzr/EcI4T7rtLhMTnFBMbfckQJBPc7UpaLTt9pxMVqO Vo7SH/q8atmp3aThT3XbEYbSvx4kUdHZYcuMogPe8T+3Bx4i9gWGnmpqF94P0Kl8 SZgY92JEhF92PwVTi7ztAfAZQDunVm60c/Lp44r0q/lGQKZLXP8jQXd7KmL6dnPI gDnispJnNdNxVSVDx/r3yjSRh0VCA3yv01ed/pusCrxX48sEw7ExwswEJBy12O3s rUY7Xx/U+eIP+E+4B7ddlzTFy+0t6HQ0q0LLtbiim1ELF+8ZBnAvCMnm49SQbpEQ UMgO/bCAGkGu88uR3sclIwUbaR9oCCxkZO0YuLvAnGoMJ7JaYQlDmDqe/lWP7VjV HEmJxDpJE9SgmVtYkfz3aOEds5nSspRQOQfQpnq/JxjRQTSfriSpDpl72d5qk1CH WHAM8lviqVg/uT6r2Q== =z0XP -----END PGP SIGNATURE----- Merge tag 'meminit-v5.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux Pull structleak fix from Kees Cook: "Disable gcc-based stack variable auto-init under KASAN (Arnd Bergmann). This fixes a bunch of build warnings under KASAN and the gcc-plugin-based stack auto-initialization features (which are arguably redundant, so better to let KASAN control this)" * tag 'meminit-v5.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux: structleak: disable STRUCTLEAK_BYREF in combination with KASAN_STACK |
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Arnd Bergmann
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173e6ee21e |
structleak: disable STRUCTLEAK_BYREF in combination with KASAN_STACK
The combination of KASAN_STACK and GCC_PLUGIN_STRUCTLEAK_BYREF
leads to much larger kernel stack usage, as seen from the warnings
about functions that now exceed the 2048 byte limit:
drivers/media/i2c/tvp5150.c:253:1: error: the frame size of 3936 bytes is larger than 2048 bytes
drivers/media/tuners/r820t.c:1327:1: error: the frame size of 2816 bytes is larger than 2048 bytes
drivers/net/wireless/broadcom/brcm80211/brcmsmac/phy/phy_n.c:16552:1: error: the frame size of 3144 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]
fs/ocfs2/aops.c:1892:1: error: the frame size of 2088 bytes is larger than 2048 bytes
fs/ocfs2/dlm/dlmrecovery.c:737:1: error: the frame size of 2088 bytes is larger than 2048 bytes
fs/ocfs2/namei.c:1677:1: error: the frame size of 2584 bytes is larger than 2048 bytes
fs/ocfs2/super.c:1186:1: error: the frame size of 2640 bytes is larger than 2048 bytes
fs/ocfs2/xattr.c:3678:1: error: the frame size of 2176 bytes is larger than 2048 bytes
net/bluetooth/l2cap_core.c:7056:1: error: the frame size of 2144 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]
net/bluetooth/l2cap_core.c: In function 'l2cap_recv_frame':
net/bridge/br_netlink.c:1505:1: error: the frame size of 2448 bytes is larger than 2048 bytes
net/ieee802154/nl802154.c:548:1: error: the frame size of 2232 bytes is larger than 2048 bytes
net/wireless/nl80211.c:1726:1: error: the frame size of 2224 bytes is larger than 2048 bytes
net/wireless/nl80211.c:2357:1: error: the frame size of 4584 bytes is larger than 2048 bytes
net/wireless/nl80211.c:5108:1: error: the frame size of 2760 bytes is larger than 2048 bytes
net/wireless/nl80211.c:6472:1: error: the frame size of 2112 bytes is larger than 2048 bytes
The structleak plugin was previously disabled for CONFIG_COMPILE_TEST,
but meant we missed some bugs, so this time we should address them.
The frame size warnings are distracting, and risking a kernel stack
overflow is generally not beneficial to performance, so it may be best
to disallow that particular combination. This can be done by turning
off either one. I picked the dependency in GCC_PLUGIN_STRUCTLEAK_BYREF
and GCC_PLUGIN_STRUCTLEAK_BYREF_ALL, as this option is designed to
make uninitialized stack usage less harmful when enabled on its own,
but it also prevents KASAN from detecting those cases in which it was
in fact needed.
KASAN_STACK is currently implied by KASAN on gcc, but could be made a
user selectable option if we want to allow combining (non-stack) KASAN
with GCC_PLUGIN_STRUCTLEAK_BYREF.
Note that it would be possible to specifically address the files that
print the warning, but presumably the overall stack usage is still
significantly higher than in other configurations, so this would not
address the full problem.
I could not test this with CONFIG_INIT_STACK_ALL, which may or may not
suffer from a similar problem.
Fixes:
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Alexander Potapenko
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6471384af2 |
mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options
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> |
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Thomas Gleixner
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ec8f24b7fa |
treewide: Add SPDX license identifier - Makefile/Kconfig
Add SPDX license identifiers to all Make/Kconfig files which: - Have no license information of any form These files fall under the project license, GPL v2 only. The resulting SPDX license identifier is: GPL-2.0-only Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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Kees Cook
|
709a972efb |
security: Implement Clang's stack initialization
CONFIG_INIT_STACK_ALL turns on stack initialization based on
-ftrivial-auto-var-init in Clang builds, which has greater coverage
than CONFIG_GCC_PLUGINS_STRUCTLEAK_BYREF_ALL.
-ftrivial-auto-var-init Clang option provides trivial initializers for
uninitialized local variables, variable fields and padding.
It has three possible values:
pattern - uninitialized locals are filled with a fixed pattern
(mostly 0xAA on 64-bit platforms, see https://reviews.llvm.org/D54604
for more details, but 0x000000AA for 32-bit pointers) likely to cause
crashes when uninitialized value is used;
zero (it's still debated whether this flag makes it to the official
Clang release) - uninitialized locals are filled with zeroes;
uninitialized (default) - uninitialized locals are left intact.
This patch uses only the "pattern" mode when CONFIG_INIT_STACK_ALL is
enabled.
Developers have the possibility to opt-out of this feature on a
per-variable basis by using __attribute__((uninitialized)), but such
use should be well justified in comments.
Co-developed-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Alexander Potapenko <glider@google.com>
Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com>
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Kees Cook
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b6a6a3772d |
security: Move stackleak config to Kconfig.hardening
This moves the stackleak plugin options to Kconfig.hardening's memory initialization menu. Signed-off-by: Kees Cook <keescook@chromium.org> Reviewed-by: Alexander Popov <alex.popov@linux.com> Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com> |
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Kees Cook
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9f671e5815 |
security: Create "kernel hardening" config area
Right now kernel hardening options are scattered around various Kconfig files. This can be a central place to collect these kinds of options going forward. This is initially populated with the memory initialization options from the gcc-plugins. Signed-off-by: Kees Cook <keescook@chromium.org> Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com> |