2015-10-09 15:42 GMT+03:00 Mark Rutland <mark.rutland@xxxxxxx>: > On Fri, Oct 09, 2015 at 01:18:09PM +0300, Andrey Ryabinin wrote: >> 2015-10-09 12:48 GMT+03:00 Mark Rutland <mark.rutland@xxxxxxx>: >> > On Fri, Oct 09, 2015 at 12:32:18PM +0300, Andrey Ryabinin wrote: >> > [...] >> > >> >> I thought the EFI stub isolation patches create a copy of mem*() functions in the stub, >> >> but they are just create aliases with __efistub_ prefix. >> >> >> >> We only need to create some more aliases for KASAN. >> >> The following patch on top of the EFI stub isolation series works for me. >> >> >> >> >> >> Signed-off-by: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx> >> >> --- >> >> arch/arm64/kernel/image.h | 6 ++++++ >> >> 1 file changed, 6 insertions(+) >> >> >> >> diff --git a/arch/arm64/kernel/image.h b/arch/arm64/kernel/image.h >> >> index e083af0..6eb8fee 100644 >> >> --- a/arch/arm64/kernel/image.h >> >> +++ b/arch/arm64/kernel/image.h >> >> @@ -80,6 +80,12 @@ __efistub_strcmp = __pi_strcmp; >> >> __efistub_strncmp = __pi_strncmp; >> >> __efistub___flush_dcache_area = __pi___flush_dcache_area; >> >> >> >> +#ifdef CONFIG_KASAN >> >> +__efistub___memcpy = __pi_memcpy; >> >> +__efistub___memmove = __pi_memmove; >> >> +__efistub___memset = __pi_memset; >> >> +#endif >> > >> > Ard's v4 stub isolation series has these aliases [1], as the stub >> > requires these aliases regardless of KASAN in order to link. >> >> Stub isolation series has __efistub_memcpy, not __efistub___memcpy >> (two additional '_'). > > Ah, I see, sorry for my sloppy reading. > >> The thing is, KASAN provides own implementation of memcpy() which >> checks memory before access. >> The original 'memcpy()' becomes __memcpy(), so we could still use it. > > Ok. > >> In code that not instrumented by KASAN (like the EFI stub) we replace >> KASAN's memcpy() with the original __mempcy(): >> #define memcpy() __memcpy() > > I'm a little confused by this. Surely that doesn't override implicit > calls generated by the compiler, leaving us with a mixture of calls to > memcpy and __memcpy? > > That doesn't matter for the stub, as both __efistub_mem* and > __efistub___mem* would point at __pe_mem*, but doesn't that matter for > other users that shouldn't be instrumented? > > Is that not a problem, or do we inhibit/override that somehow? > You are right, GCC could emit memcpy() call. It's just not a problem so far. The amount of not instrumented code is fairly small (some low-level x86 code, kasan internals and slub allocator). The purpose of these defines is to not spread kasan-specific details across unrelated code. E.g. there are a lot of memcpy()/memset() calls in slub that used to access object's redzone or freed objects. So it simpler to redefine memset, rather then somehow mangle that code. >> So with CONFIG_KASAN=y the EFI stub uses __memcpy, thus we need to >> create the __efistub___memcpy alias. > > Ok, that makes sense to me. > > Thanks, > Mark. -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
