linux-kernel - Re: [PATCH v2] s390/fpu: Fix false-positive kmsan report in fpu

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Message-ID: <20251110093017.15528A26-hca@linux.ibm.com>
Date: Mon, 10 Nov 2025 10:30:17 +0100
From: Heiko Carstens <hca@...ux.ibm.com>
To: Aleksei Nikiforov <aleksei.nikiforov@...ux.ibm.com>
Cc: Alexander Potapenko <glider@...gle.com>, Marco Elver <elver@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>, Thomas Huth <thuth@...hat.com>,
        Juergen Christ <jchrist@...ux.ibm.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>
Subject: Re: [PATCH v2] s390/fpu: Fix false-positive kmsan report in fpu_vstl
 function

On Fri, Nov 07, 2025 at 04:59:16PM +0100, Aleksei Nikiforov wrote:
> A false-positive kmsan report is detected when running ping command.
> 
> An inline assembly instruction 'vstl' can write varied amount of bytes
> depending on value of 'index' argument. If 'index' > 0, 'vstl' writes
> at least 2 bytes.
> 
> clang generates kmsan write helper call depending on inline assembly
> constraints. Constraints are evaluated compile-time, but value of
> 'index' argument is known only at runtime.
> 
> clang currently generates call to __msan_instrument_asm_store with 1 byte
> as size. Manually call kmsan function to indicate correct amount of bytes
> written and fix false-positive report.
...
> Fixes: dcd3e1de9d17 ("s390/checksum: provide csum_partial_copy_nocheck()")
> Signed-off-by: Aleksei Nikiforov <aleksei.nikiforov@...ux.ibm.com>
> ---
>  arch/s390/include/asm/fpu-insn.h | 3 +++
>  1 file changed, 3 insertions(+)

Applied, thanks!