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

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Message-ID: <20250917154845.GA70934@quark>
Date: Wed, 17 Sep 2025 10:48:45 -0500
From: Eric Biggers <ebiggers@...nel.org>
To: Alexander Potapenko <glider@...gle.com>
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

On Wed, Sep 17, 2025 at 10:31:31AM +0200, Alexander Potapenko wrote:
> > > > > 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?

I attached the kconfig I used.

- Eric

View attachment ".config" of type "text/plain" (81119 bytes)