linux-kernel - Re: [PATCH 07/43] compiler_attributes.h: add __disable_sanitizer

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Date:   Wed, 15 Dec 2021 13:24:04 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Christoph Hellwig <hch@....de>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Pekka Enberg <penberg@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/43] compiler_attributes.h: add
 __disable_sanitizer_instrumentation

On Tue, Dec 14, 2021 at 05:20:14PM +0100, Alexander Potapenko wrote:
> The new attribute maps to
> __attribute__((disable_sanitizer_instrumentation)), which will be
> supported by Clang >= 14.0. Future support in GCC is also possible.
> 
> This attribute disables compiler instrumentation for kernel sanitizer
> tools, making it easier to implement noinstr. It is different from the
> existing __no_sanitize* attributes, which may still allow certain types
> of instrumentation to prevent false positives.

When you say the __no_sanitize* attributes allow some instrumentation, does
that apply to any of the existing KASAN/KCSAN/KCOV support, or just for KMSAN?

The documentation just says the same as the commit message:

| This is not the same as __attribute__((no_sanitize(...))), which depending on
| the tool may still insert instrumentation to prevent false positive reports.

... which implies the other instrumentation might not be suprressed.

I ask because architectures which select ARCH_WANTS_NO_INSTR *need* to be able
to suppress all instrumentation. It's fine if that means they need a new
version of clang for KMSAN, but if there's latent instrumentation we have more
bugs to fix first...

Thanks,
Mark.

> Signed-off-by: Alexander Potapenko <glider@...gle.com>
> ---
> Link: https://linux-review.googlesource.com/id/Ic0123ce99b33ab7d5ed1ae90593425be8d3d774a
> ---
>  include/linux/compiler_attributes.h | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
> index b9121afd87331..37e2600202216 100644
> --- a/include/linux/compiler_attributes.h
> +++ b/include/linux/compiler_attributes.h
> @@ -308,6 +308,24 @@
>  # define __compiletime_warning(msg)
>  #endif
>  
> +/*
> + * Optional: only supported since clang >= 14.0
> + *
> + * clang: https://clang.llvm.org/docs/AttributeReference.html#disable-sanitizer-instrumentation
> + *
> + * disable_sanitizer_instrumentation is not always similar to
> + * no_sanitize((<sanitizer-name>)): the latter may still let specific sanitizers
> + * insert code into functions to prevent false positives. Unlike that,
> + * disable_sanitizer_instrumentation prevents all kinds of instrumentation to
> + * functions with the attribute.
> + */
> +#if __has_attribute(disable_sanitizer_instrumentation)
> +# define __disable_sanitizer_instrumentation \
> +	 __attribute__((disable_sanitizer_instrumentation))
> +#else
> +# define __disable_sanitizer_instrumentation
> +#endif
> +
>  /*
>   *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-weak-function-attribute
>   *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-weak-variable-attribute
> -- 
> 2.34.1.173.g76aa8bc2d0-goog
>