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Subject: Re: [PATCH v2 13/33] kmsan: Introduce memset_no_sanitize_memory()
From:   Ilya Leoshkevich <iii@linux.ibm.com>
To:     Alexander Potapenko <glider@google.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>
Date:   Wed, 13 Dec 2023 12:32:59 +0100
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On Wed, 2023-12-13 at 02:31 +0100, Ilya Leoshkevich wrote:
> On Fri, 2023-12-08 at 16:25 +0100, Alexander Potapenko wrote:
> > > A problem with __memset() is that, at least for me, it always
> > > ends
> > > up being a call. There is a use case where we need to write only
> > > 1
> > > byte, so I thought that introducing a call there (when compiling
> > > without KMSAN) would be unacceptable.

[...]

> > As stated above, I don't think this is more or less working as
> > intended.
> > If we really want the ability to inline __memset(), we could
> > transform
> > it into memset() in non-sanitizer builds, but perhaps having a call
> > is
> > also acceptable?
>=20
> Thanks for the detailed explanation and analysis. I will post
> a version with a __memset() and let the slab maintainers decide if
> the additional overhead is acceptable.

I noticed I had the same problem in the get_user()/put_user() and
check_canary() patches.

The annotation being silently ignored is never what a programmer
intends, so what do you think about adding noinline to
__no_kmsan_checks and __no_sanitize_memory?