linux-kernel - Re: [PATCH 12/32] kmsan: Allow disabling KMSAN checks for the current task

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Message-ID: <8fb810e5000dd66334a4a686407c0caeacb79f55.camel@linux.ibm.com>
Date:   Thu, 16 Nov 2023 10:17:20 +0100
From:   Ilya Leoshkevich <iii@...ux.ibm.com>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     Alexander Gordeev <agordeev@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.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 12/32] kmsan: Allow disabling KMSAN checks for the
 current task

On Thu, 2023-11-16 at 09:56 +0100, Alexander Potapenko wrote:
> On Wed, Nov 15, 2023 at 9:34 PM Ilya Leoshkevich <iii@...ux.ibm.com>
> wrote:
> > 
> > Like for KASAN, it's useful to temporarily disable KMSAN checks
> > around,
> > e.g., redzone accesses.
> 
> This example is incorrect, because KMSAN does not have redzones.
> You are calling these functions from "mm: slub: Let KMSAN access
> metadata", which mentiones redzones in kfree(), but the description
> is
> still somewhat unclear.
> Can you provide more insight about what is going on? Maybe we can fix
> those accesses instead of disabling KMSAN?

It's about SLUB redzones, which appear when compiling with
CONFIG_DEBUG_SLAB.

I think that from KMSAN's point of view they should be considered
poisoned, but then the question is what to do with functions that check
them. I noticed that there was special handling for KASAN there
already, so I figured that the best solution would be to do the same
thing for KMSAN.