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

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Message-ID: <Y+ouq8ooI7UH4cL+@hirez.programming.kicks-ass.net>
Date:   Mon, 13 Feb 2023 13:35:55 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jakub Jelinek <jakub@...hat.com>
Cc:     Marco Elver <elver@...gle.com>,
        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 Mon, Feb 13, 2023 at 12:01:40PM +0100, Jakub Jelinek wrote:

> The current gcc behavior is that operations like aggregate copies, or
> clearing which might or might not need memcpy/memset/memmove under the hood
> later are asan instrumented before the operation (in order not to limit the
> choices on how it will be expanded), uses of builtins (__builtin_ prefixed
> or not) are also instrumented before the calls unless they are one of the
> calls that is recognized as always instrumented.  None for hwasan,
> for asan:
> index, memchr, memcmp, memcpy, memmove, memset, strcasecmp, strcat, strchr,
> strcmp, strcpy, strdup, strlen, strncasecmp, strncat, strncmp, strcspn,
> strpbrk, strspn, strstr, strncpy
> and for those builtins gcc disables inline expansion and enforces a library
> call (but until the expansion they are treated in optimizations like normal
> builtins and so could be say DCEd, or their aliasing behavior is considered
> etc.).  kasan behaves the same I think.
> 
> Now, I think libasan only has __asan_ prefixed
> __asan_memmove, __asan_memset and __asan_memcpy, nothing else, so most of
> the calls from the above list even can't be prefixed.
> 
> So, do you want for --param asan-kernel-mem-intrinsic-prefix=1 to __asan_
> prefix just memcpy/memmove/memset and nothing else?  Is it ok to emit
> memcpy/memset/memmove from aggregate operations which are instrumented
> already at the caller (and similarly is it ok to handle those operations
> inline)?

I'm thinking it is trivial to add more __asan prefixed functions as
needed, while trying to untangle the trainwreck created by assuming the
normal functions are instrumented is much more work.