From: Daniel Axtens <dja@axtens.net>
To: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
kasan-dev@googlegroups.com
Cc: linux-s390@vger.kernel.org, linux-xtensa@linux-xtensa.org,
x86@kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-arm-kernel@lists.infradead.org,
Daniel Axtens <dja@axtens.net>
Subject: [PATCH 0/2] Fix some incompatibilites between KASAN and FORTIFY_SOURCE
Date: Wed, 15 Jan 2020 17:37:08 +1100 [thread overview]
Message-ID: <20200115063710.15796-1-dja@axtens.net> (raw)
3 KASAN self-tests fail on a kernel with both KASAN and FORTIFY_SOURCE:
memchr, memcmp and strlen. I have observed this on x86 and powerpc.
When FORTIFY_SOURCE is on, a number of functions are replaced with
fortified versions, which attempt to check the sizes of the
operands. However, these functions often directly invoke __builtin_foo()
once they have performed the fortify check.
This breaks things in 2 ways:
- the three function calls are technically dead code, and can be
eliminated. When __builtin_ versions are used, the compiler can detect
this.
- Using __builtins may bypass KASAN checks if the compiler decides to
inline it's own implementation as sequence of instructions, rather than
emit a function call that goes out to a KASAN-instrumented
implementation.
The patches address each reason in turn.
As a result, we're also able to remove a snippet of code copy-pasted
between every KASAN implementation that tries (largely unsuccessfully) to
disable FORTIFY_SOURCE under KASAN.
Daniel Axtens (2):
kasan: stop tests being eliminated as dead code with FORTIFY_SOURCE
string.h: fix incompatibility between FORTIFY_SOURCE and KASAN
arch/arm64/include/asm/string.h | 4 ---
arch/powerpc/include/asm/string.h | 4 ---
arch/s390/include/asm/string.h | 4 ---
arch/x86/include/asm/string_64.h | 4 ---
arch/xtensa/include/asm/string.h | 3 --
include/linux/string.h | 49 +++++++++++++++++++++++--------
lib/test_kasan.c | 30 ++++++++++++-------
7 files changed, 56 insertions(+), 42 deletions(-)
--
2.20.1
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next reply other threads:[~2020-01-15 6:37 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-15 6:37 Daniel Axtens [this message]
2020-01-15 6:37 ` [PATCH 1/2] kasan: stop tests being eliminated as dead code with FORTIFY_SOURCE Daniel Axtens
2020-01-15 14:43 ` Dmitry Vyukov
2020-01-15 14:47 ` Christophe Leroy
2020-01-15 14:57 ` Dmitry Vyukov
2020-01-16 5:34 ` Daniel Axtens
2020-01-15 6:37 ` [PATCH 2/2] string.h: fix incompatibility between FORTIFY_SOURCE and KASAN Daniel Axtens
2020-01-15 14:56 ` Dmitry Vyukov
2020-01-16 4:59 ` Daniel Axtens
2020-01-16 5:47 ` Dmitry Vyukov
2020-01-16 23:52 ` kbuild test robot
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