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

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Message-ID: <CAG_fn=W_7o6ANs94GwoYjyjvY5kSFYHB6DwfE+oXM7TP1eP5dw@mail.gmail.com>
Date: Thu, 11 Sep 2025 11:09:17 +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
Subject: Re: [PATCH] kmsan: Fix out-of-bounds access to shadow memory

On Wed, Sep 10, 2025 at 9:49 PM Eric Biggers <ebiggers@...nel.org> wrote:
>
> On Fri, Aug 29, 2025 at 09:45:00AM -0700, Eric Biggers wrote:
> > Running sha224_kunit on a KMSAN-enabled kernel results in a crash in
> > kmsan_internal_set_shadow_origin():
> >
> >     BUG: unable to handle page fault for address: ffffbc3840291000
> >     #PF: supervisor read access in kernel mode
> >     #PF: error_code(0x0000) - not-present page
> >     PGD 1810067 P4D 1810067 PUD 192d067 PMD 3c17067 PTE 0
> >     Oops: 0000 [#1] SMP NOPTI
> >     CPU: 0 UID: 0 PID: 81 Comm: kunit_try_catch Tainted: G                 N  6.17.0-rc3 #10 PREEMPT(voluntary)
> >     Tainted: [N]=TEST
> >     Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014
> >     RIP: 0010:kmsan_internal_set_shadow_origin+0x91/0x100
> >     [...]
> >     Call Trace:
> >     <TASK>
> >     __msan_memset+0xee/0x1a0
> >     sha224_final+0x9e/0x350
> >     test_hash_buffer_overruns+0x46f/0x5f0
> >     ? kmsan_get_shadow_origin_ptr+0x46/0xa0
> >     ? __pfx_test_hash_buffer_overruns+0x10/0x10
> >     kunit_try_run_case+0x198/0xa00
>
> Any thoughts on this patch from the KMSAN folks?  I'd love to add
> CONFIG_KMSAN=y to my crypto subsystem testing, but unfortunately the
> kernel crashes due to this bug :-(
>
> - Eric

Sorry, I was out in August and missed this email when digging through my inbox.

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?


--
Alexander Potapenko
Software Engineer

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