linux-kernel - Re: [PATCH] kmsan: Fix out-of-bounds access to shadow memory

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Message-ID: <CAG_fn=WNgF3MU1cur7ddp_BPwXQEtpAOLSK1hQuigd1dYvj70Q@mail.gmail.com>
Date: Wed, 17 Sep 2025 10:31:31 +0200
From: Alexander Potapenko <glider@...gle.com>
To: Eric Biggers <ebiggers@...nel.org>
Cc: Marco Elver <elver@...gle.com>, kasan-dev@...glegroups.com, 
	Dmitry Vyukov <dvyukov@...gle.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	linux-crypto@...r.kernel.org, stable@...r.kernel.org, 
	Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH] kmsan: Fix out-of-bounds access to shadow memory

> > > > Curiously, I couldn't find any relevant crashes on the KMSAN syzbot
> > > > instance, but the issue is legit.
> > > > Thank you so much for fixing this!
> > > >
> > > > Any chance you can add a test case for it to mm/kmsan/kmsan_test.c?
> > >
> > > Unfortunately most of the KMSAN test cases already fail on upstream,
> > > which makes it difficult to develop new ones:
> >
> > The KMSAN test failures bisect to the following commit:
> >
> >     commit f90b474a35744b5d43009e4fab232e74a3024cae
> >     Author: Vlastimil Babka <vbabka@...e.cz>
> >     Date:   Mon Mar 10 13:40:17 2025 +0100
> >
> >         mm: Fix the flipped condition in gfpflags_allow_spinning()
> >
> > I'm not sure why.  Apparently something related to lib/stackdepot.c.
> >
> > Reverting that commit on top of upstream fixes the KMSAN tests.
> >
>
> Rolling back all the BPF (?) related changes that were made to
> lib/stackdepot.c in v6.15 fixes this too.  Looks like there was a
> regression where stack traces stopped being saved in some cases.

Hmm, the tests don't fail for me on v6.17-rc5 with the attached config.
Could you share yours?

View attachment "config.txt" of type "text/plain" (273300 bytes)