On Thu, Apr 23, 2020 at 11:45 PM Daniel Axtens <dja@xxxxxxxxxx> wrote: > > 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. Finally, test_memcmp used a > stack array without explicit initialisation, which can sometimes break > too, so fix that up. > > v3: resend with Reviewed-bys, hopefully for inclusion in 5.8. > > v2: - some cleanups, don't mess with arch code as I missed some wrinkles. > - add stack array init (patch 3) > > Daniel Axtens (3): > kasan: stop tests being eliminated as dead code with FORTIFY_SOURCE > string.h: fix incompatibility between FORTIFY_SOURCE and KASAN > kasan: initialise array in kasan_memcmp test > > include/linux/string.h | 60 +++++++++++++++++++++++++++++++++--------- > lib/test_kasan.c | 32 +++++++++++++--------- > 2 files changed, 68 insertions(+), 24 deletions(-) > > -- > 2.20.1 > > -- > You received this message because you are subscribed to the Google Groups "kasan-dev" group. > To unsubscribe from this group and stop receiving emails from it, send an email to kasan-dev+unsubscribe@xxxxxxxxxxxxxxxx. > To view this discussion on the web visit https://groups.google.com/d/msgid/kasan-dev/20200423154503.5103-1-dja%40axtens.net. Thanks, Daniel! For the series: Tested-by: David Gow <davidgow@xxxxxxxxxx> (Though I will mirror Dmitry's comment[1] on patch 3 -- I also have a memset() already present in my branch...) I'd been digging into what turns out to be this issue, which we were seeing sporadically[2] with the KUnit port of these tests. v7 of the KUnit port[3] includes your changes, and fixes the issues. Cheers, -- David [1]: https://lkml.org/lkml/2020/4/23/838 [2]: https://lkml.org/lkml/2020/4/18/570 [3]: https://lkml.org/lkml/2020/4/24/80
