linux-kernel - Re: [PATCH] mips: cm: Convert to bitfield API to fix out-of-bounds access

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Message-ID: <20211102102137.GB7512@alpha.franken.de>
Date:   Tue, 2 Nov 2021 11:21:37 +0100
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     Markos Chandras <markos.chandras@...tec.com>,
        Ralf Baechle <ralf@...ux-mips.org>, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mips: cm: Convert to bitfield API to fix out-of-bounds
 access

On Fri, Oct 29, 2021 at 11:58:16AM +0200, Geert Uytterhoeven wrote:
> mips_cm_error_report() extracts the cause and other cause from the error
> register using shifts.  This works fine for the former, as it is stored
> in the top bits, and the shift will thus remove all non-related bits.
> However, the latter is stored in the bottom bits, hence thus needs masking
> to get rid of non-related bits.  Without such masking, using it as an
> index into the cm2_causes[] array will lead to an out-of-bounds access,
> probably causing a crash.
> 
> Fix this by using FIELD_GET() instead.  Bite the bullet and convert all
> MIPS CM handling to the bitfield API, to improve readability and safety.
> 
> Fixes: 3885c2b463f6a236 ("MIPS: CM: Add support for reporting CM cache errors")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
> Compile-tested only, but assembler output before/after compared.
> ---
>  arch/mips/include/asm/mips-cm.h | 12 ++++++------
>  arch/mips/kernel/mips-cm.c      | 21 ++++++++++-----------
>  2 files changed, 16 insertions(+), 17 deletions(-)

applied to mips-next.

Thomas.

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