linux-kernel - Re: [PATCH v2 17/33] mm: kfence: Disable KMSAN when checking the canary

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Message-ID: <CAG_fn=XbDFa_7BWMzR5cVEVp-GuHxK2fyFAZJgXqXb8qL1ZhAA@mail.gmail.com>
Date:   Fri, 8 Dec 2023 14:55:56 +0100
From:   Alexander Potapenko <glider@...gle.com>
To:     Ilya Leoshkevich <iii@...ux.ibm.com>
Cc:     Alexander Gordeev <agordeev@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Marco Elver <elver@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Pekka Enberg <penberg@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-s390@...r.kernel.org,
        linux-trace-kernel@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Sven Schnelle <svens@...ux.ibm.com>
Subject: Re: [PATCH v2 17/33] mm: kfence: Disable KMSAN when checking the canary

On Fri, Dec 8, 2023 at 1:53 PM Alexander Potapenko <glider@...gle.com> wrote:
>
> On Tue, Nov 21, 2023 at 11:02 PM Ilya Leoshkevich <iii@...ux.ibm.com> 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@...ux.ibm.com>
> Reviewed-by: Alexander Potapenko <glider@...gle.com>

and even

Tested-by: Alexander Potapenko <glider@...gle.com>