On Fri, 10 Feb 2023 at 17:13, Andrey Konovalov <andreyknvl@xxxxxxxxx> wrote: [...] > > Probably the same should be done for SW_TAGS, because arm64 will be > > GENERIC_ENTRY at one point or another as well. > > Yes, makes sense. I'll file a bug for this once I fully understand the > consequences of these changes. > > > KASAN + GCC on x86 will have no mem*() instrumentation after > > 69d4c0d32186, which is sad, so somebody ought to teach it the same > > param as above. > > Hm, with that patch we would have no KASAN checking within normal mem* > functions (not the ones embedded by the compiler) on GENERIC_ENTRY > arches even with Clang, right? Yes, that's the point - normal mem*() functions cannot be instrumented with GENERIC_ENTRY within noinstr functions, because the compiler sometimes decides to transform normal assignments into memcpy()/memset(). And if mem*() were instrumented (as it was before 69d4c0d32186), that'd break things for these architectures. But since most code is normally instrumented, with the right compiler support (which the patch here enables), we just turn mem*() in instrumented functions into __asan_mem*(), and get the instrumentation as before. 69d4c0d32186 already added those __asan functions. The fact that KASAN used to override mem*() is just the wrong choice in a world where compilers decide to inline or outline these. From an instrumentation point of view at the compiler level, we need to treat them like any other instrumentable instruction (loads, stores, atomics, etc.): transform each instrumentable instruction into something that does the right checks. Only then can we be sure that we don't accidentally instrument something that shouldn't be (noinstr functions), because instead of relying on the compiler, we forced instrumentation on every mem*().
