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From:   Alexander Potapenko <glider@google.com>
Date:   Fri, 8 Dec 2023 14:48:55 +0100
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Subject: Re: [PATCH v2 13/33] kmsan: Introduce memset_no_sanitize_memory()
To:     Ilya Leoshkevich <iii@linux.ibm.com>
Cc:     Alexander Gordeev <agordeev@linux.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Marco Elver <elver@google.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Pekka Enberg <penberg@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>,
        kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-s390@vger.kernel.org,
        linux-trace-kernel@vger.kernel.org,
        Mark Rutland <mark.rutland@arm.com>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Sven Schnelle <svens@linux.ibm.com>
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On Tue, Nov 21, 2023 at 11:06=E2=80=AFPM Ilya Leoshkevich <iii@linux.ibm.co=
m> wrote:
>
> Add a wrapper for memset() that prevents unpoisoning.

We have __memset() already, won't it work for this case?
On the other hand, I am not sure you want to preserve the redzone in
its previous state (unless it's known to be poisoned).
You might consider explicitly unpoisoning the redzone instead.

...

> +__no_sanitize_memory
> +static inline void *memset_no_sanitize_memory(void *s, int c, size_t n)
> +{
> +       return memset(s, c, n);
> +}

I think depending on the compiler optimizations this might end up
being a call to normal memset, that would still change the shadow
bytes.