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References: <20231121220155.1217090-1-iii@linux.ibm.com> <20231121220155.1217090-18-iii@linux.ibm.com>
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From:   Alexander Potapenko <glider@google.com>
Date:   Fri, 8 Dec 2023 13:53:41 +0100
Message-ID: <CAG_fn=Ug6MFyoj=J_yabfd-V+3vGYNS3-CS+fhW9Tsc847xMtw@mail.gmail.com>
Subject: Re: [PATCH v2 17/33] mm: kfence: Disable KMSAN when checking the canary
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 11:02=E2=80=AFPM Ilya Leoshkevich <iii@linux.ibm.co=
m> wrote:
>
> KMSAN warns about check_canary() accessing the canary.
>
> The reason is that, even though set_canary() is properly instrumented
> and sets shadow, slub explicitly poisons the canary's address range
> afterwards.
>
> Unpoisoning the canary is not the right thing to do: only
> check_canary() is supposed to ever touch it. Instead, disable KMSAN
> checks around canary read accesses.
>
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Alexander Potapenko <glider@google.com>