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From:   Marco Elver <elver@google.com>
Date:   Thu, 8 Sep 2022 08:05:17 +0200
Message-ID: <CANpmjNMH4_H75Z_aQ63C52TDma7PnjWWjmyv+MtXt2W522UAQQ@mail.gmail.com>
Subject: Re: [PATCH 1/2] kcsan: Instrument memcpy/memset/memmove with newer Clang
To:     elver@google.com, "Paul E. McKenney" <paulmck@kernel.org>
Cc:     Mark Rutland <mark.rutland@arm.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Alexander Potapenko <glider@google.com>,
        Boqun Feng <boqun.feng@gmail.com>, kasan-dev@googlegroups.com,
        linux-kernel@vger.kernel.org,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        llvm@lists.linux.dev, stable@vger.kernel.org
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On Wed, 7 Sept 2022 at 19:39, Marco Elver <elver@google.com> wrote:
>
> With Clang version 16+, -fsanitize=thread will turn
> memcpy/memset/memmove calls in instrumented functions into
> __tsan_memcpy/__tsan_memset/__tsan_memmove calls respectively.
>
> Add these functions to the core KCSAN runtime, so that we (a) catch data
> races with mem* functions, and (b) won't run into linker errors with
> such newer compilers.
>
> Cc: stable@vger.kernel.org # v5.10+
> Signed-off-by: Marco Elver <elver@google.com>
> ---
>  kernel/kcsan/core.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
>
> diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
> index fe12dfe254ec..66ef48aa86e0 100644
> --- a/kernel/kcsan/core.c
> +++ b/kernel/kcsan/core.c
> @@ -18,6 +18,7 @@
>  #include <linux/percpu.h>
>  #include <linux/preempt.h>
>  #include <linux/sched.h>
> +#include <linux/string.h>
>  #include <linux/uaccess.h>
>
>  #include "encoding.h"
> @@ -1308,3 +1309,29 @@ noinline void __tsan_atomic_signal_fence(int memorder)
>         }
>  }
>  EXPORT_SYMBOL(__tsan_atomic_signal_fence);
> +
> +void *__tsan_memset(void *s, int c, size_t count);
> +noinline void *__tsan_memset(void *s, int c, size_t count)
> +{
> +       check_access(s, count, KCSAN_ACCESS_WRITE, _RET_IP_);
> +       return __memset(s, c, count);
> +}
> +EXPORT_SYMBOL(__tsan_memset);
> +
> +void *__tsan_memmove(void *dst, const void *src, size_t len);
> +noinline void *__tsan_memmove(void *dst, const void *src, size_t len)
> +{
> +       check_access(dst, len, KCSAN_ACCESS_WRITE, _RET_IP_);
> +       check_access(src, len, 0, _RET_IP_);
> +       return __memmove(dst, src, len);
> +}
> +EXPORT_SYMBOL(__tsan_memmove);
> +
> +void *__tsan_memcpy(void *dst, const void *src, size_t len);
> +noinline void *__tsan_memcpy(void *dst, const void *src, size_t len)
> +{
> +       check_access(dst, len, KCSAN_ACCESS_WRITE, _RET_IP_);
> +       check_access(src, len, 0, _RET_IP_);
> +       return __memcpy(dst, src, len);
> +}
> +EXPORT_SYMBOL(__tsan_memcpy);

I missed that s390 doesn't have arch memcpy variants, so this fails:

>> kernel/kcsan/core.c:1316:16: error: implicit declaration of function '__memset'; did you mean '__memset64'? [-Werror=implicit-function-declaration]

I'll send a v2 where __tsan_mem* is aliased to generic versions if the
arch doesn't have mem*() functions.


> --
> 2.37.2.789.g6183377224-goog
>