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Date:   Mon, 23 Oct 2023 10:25:52 +0200
From:   Miquel Raynal <miquel.raynal@bootlin.com>
To:     Linus Walleij <linus.walleij@linaro.org>
Cc:     Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org, Nicolas Pitre <nico@fluxnic.net>
Subject: Re: [PATCH v4] mtd: cfi_cmdset_0001: Byte swap OTP info
Message-ID: <20231023102552.4b053b17@xps-13>
In-Reply-To: <20231020-mtd-otp-byteswap-v4-1-0d132c06aa9d@linaro.org>
References: <20231020-mtd-otp-byteswap-v4-1-0d132c06aa9d@linaro.org>
Organization: Bootlin
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Hi Linus,

linus.walleij@linaro.org wrote on Fri, 20 Oct 2023 22:30:29 +0200:

> Currently the offset into the device when looking for OTP
> bits can go outside of the address of the MTD NOR devices,
> and if that memory isn't readable, bad things happen
> on the IXP4xx (added prints that illustrate the problem before
> the crash):
>=20
> cfi_intelext_otp_walk walk OTP on chip 0 start at reg_prot_offset 0x00000=
100
> ixp4xx_copy_from copy from 0x00000100 to 0xc880dd78
> cfi_intelext_otp_walk walk OTP on chip 0 start at reg_prot_offset 0x12000=
000
> ixp4xx_copy_from copy from 0x12000000 to 0xc880dd78
> 8<--- cut here ---
> Unable to handle kernel paging request at virtual address db000000
> [db000000] *pgd=3D00000000
> (...)
>=20
> This happens in this case because the IXP4xx is big endian and
> the 32- and 16-bit fields in the struct cfi_intelext_otpinfo are not
> properly byteswapped. Compare to how the code in read_pri_intelext()
> byteswaps the fields in struct cfi_pri_intelext.
>=20
> Adding a small byte swapping loop for the OTP in read_pri_intelext()
> and the crash goes away.
>=20
> The problem went unnoticed for many years until I enabled
> CONFIG_MTD_OTP on the IXP4xx as well, triggering the bug.
>=20
> Cc: stable@vger.kernel.org

Would you like to add a Fixes tag as well? Or is this skipped on
purpose?

> Reviewed-by: Nicolas Pitre <nico@fluxnic.net>
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---
> ChangeLog v3->v4:
> - Collected Nico's ACK.
> - Stalled since june! Has this been missed?

Our current organization relies on Vignesh to pick-up (or tell me to
pick-up) cfi patches. But he is slightly less active these days, so if I
don't get any feedback from him soon I will take it for the next merge
window.

Sorry for the delay anyway.

Cheers,
Miqu=C3=A8l