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