linux-kernel - Re: [PATCH -tip] kasan: Emit different calls for instrumentable memintrinsics

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Message-ID: <Y+aaDP32wrsd8GZq@tucnak>
Date:   Fri, 10 Feb 2023 20:25:00 +0100
From:   Jakub Jelinek <jakub@...hat.com>
To:     Marco Elver <elver@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        linux-kbuild@...r.kernel.org, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Tony Lindgren <tony@...mide.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-toolchains@...r.kernel.org
Subject: Re: [PATCH -tip] kasan: Emit different calls for instrumentable
 memintrinsics

On Wed, Feb 08, 2023 at 07:42:03PM +0100, Marco Elver wrote:
> Clang 15 will provide an option to prefix calls to memcpy/memset/memmove
> with __asan_ in instrumented functions: https://reviews.llvm.org/D122724
> 
> GCC does not yet have similar support.

GCC has support to rename memcpy/memset etc. for years, say on
following compiled with
-fsanitize=kernel-address -O2 -mstringop-strategy=libcall
(the last option just to make sure the compiler doesn't prefer to emit
rep mov*/stos* or loop or something similar, of course kernel can keep
whatever it uses) you'll get just __asan_memcpy/__asan_memset calls,
no memcpy/memset, while without -fsanitize=kernel-address you get
normally memcpy/memset.
Or do you need the __asan_* functions only in asan instrumented functions
and normal ones in non-instrumented functions in the same TU?

#ifdef __SANITIZE_ADDRESS__
extern __typeof (__builtin_memcpy) memcpy __asm ("__asan_memcpy");
extern __typeof (__builtin_memset) memset __asm ("__asan_memset");
#endif
struct S { char a[2048]; } a, b;

void
foo (void)
{
  a = b;
  b = (struct S) {};
}

void
bar (void *p, void *q, int s)
{
  memcpy (p, q, s);
}

void
baz (void *p, int c, int s)
{
  memset (p, c, s);
}

void
qux (void *p, void *q, int s)
{
  __builtin_memcpy (p, q, s);
}

void
quux (void *p, int c, int s)
{
  __builtin_memset (p, c, s);
}

	Jakub