linux-kernel - Re: [PATCH 09/43] kmsan: introduce __no_sanitize_memory and __no_kmsan

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Date:   Wed, 15 Dec 2021 13:27:42 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Alexander Potapenko <glider@...gle.com>
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>,
        Marco Elver <elver@...gle.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Pekka Enberg <penberg@...nel.org>,
        Peter Zijlstra <peterz@...radead.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 09/43] kmsan: introduce __no_sanitize_memory and
 __no_kmsan_checks

On Tue, Dec 14, 2021 at 05:20:16PM +0100, Alexander Potapenko wrote:
> __no_sanitize_memory is a function attribute that instructs KMSAN to
> skip a function during instrumentation. This is needed to e.g. implement
> the noinstr functions.
> 
> __no_kmsan_checks is a function attribute that makes KMSAN
> ignore the uninitialized values coming from the function's
> inputs, and initialize the function's outputs.
> 
> Functions marked with this attribute can't be inlined into functions
> not marked with it, and vice versa.

Just to check, I assume an unmarked __always_inline() function can be inlined
into a marked function? Otherwise this is going to be really painful to manage
for low-level helper functions.

Thanks,
Mark.

> 
> __SANITIZE_MEMORY__ is a macro that's defined iff the file is
> instrumented with KMSAN. This is not the same as CONFIG_KMSAN, which is
> defined for every file.
> 
> Signed-off-by: Alexander Potapenko <glider@...gle.com>
> ---
> Link: https://linux-review.googlesource.com/id/I004ff0360c918d3cd8b18767ddd1381c6d3281be
> ---
>  include/linux/compiler-clang.h | 23 +++++++++++++++++++++++
>  include/linux/compiler-gcc.h   |  6 ++++++
>  2 files changed, 29 insertions(+)
> 
> diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
> index 3c4de9b6c6e3e..5f11a6f269e28 100644
> --- a/include/linux/compiler-clang.h
> +++ b/include/linux/compiler-clang.h
> @@ -51,6 +51,29 @@
>  #define __no_sanitize_undefined
>  #endif
>  
> +#if __has_feature(memory_sanitizer)
> +#define __SANITIZE_MEMORY__
> +/*
> + * Unlike other sanitizers, KMSAN still inserts code into functions marked with
> + * no_sanitize("kernel-memory"). Using disable_sanitizer_instrumentation
> + * provides the behavior consistent with other __no_sanitize_ attributes,
> + * guaranteeing that __no_sanitize_memory functions remain uninstrumented.
> + */
> +#define __no_sanitize_memory __disable_sanitizer_instrumentation
> +
> +/*
> + * The __no_kmsan_checks attribute ensures that a function does not produce
> + * false positive reports by:
> + *  - initializing all local variables and memory stores in this function;
> + *  - skipping all shadow checks;
> + *  - passing initialized arguments to this function's callees.
> + */
> +#define __no_kmsan_checks __attribute__((no_sanitize("kernel-memory")))
> +#else
> +#define __no_sanitize_memory
> +#define __no_kmsan_checks
> +#endif
> +
>  /*
>   * Support for __has_feature(coverage_sanitizer) was added in Clang 13 together
>   * with no_sanitize("coverage"). Prior versions of Clang support coverage
> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
> index ccbbd31b3aae5..f6e69387aad05 100644
> --- a/include/linux/compiler-gcc.h
> +++ b/include/linux/compiler-gcc.h
> @@ -129,6 +129,12 @@
>  #define __SANITIZE_ADDRESS__
>  #endif
>  
> +/*
> + * GCC does not support KMSAN.
> + */
> +#define __no_sanitize_memory
> +#define __no_kmsan_checks
> +
>  /*
>   * Turn individual warnings and errors on and off locally, depending
>   * on version.
> -- 
> 2.34.1.173.g76aa8bc2d0-goog
>