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Date:   Thu, 1 Jun 2023 18:34:20 +0100
From:   Conor Dooley <conor@kernel.org>
To:     Kees Cook <keescook@chromium.org>
Cc:     Paul Walmsley <paul.walmsley@sifive.com>,
        Thorsten Leemhuis <linux@leemhuis.info>,
        Joan Bruguera =?iso-8859-1?Q?Mic=F3?= <joanbrugueram@gmail.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Conor Dooley <conor.dooley@microchip.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Alyssa Ross <hi@alyssa.is>,
        Heiko Stuebner <heiko.stuebner@vrull.eu>,
        "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        linux-riscv@lists.infradead.org,
        Andrew Jones <ajones@ventanamicro.com>,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH v2] riscv/purgatory: Do not use fortified string functions
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References: <20230601160025.gonna.868-kees@kernel.org>
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On Thu, Jun 01, 2023 at 09:00:28AM -0700, Kees Cook wrote:
> With the addition of -fstrict-flex-arrays=3D3, struct sha256_state's
> trailing array is no longer ignored by CONFIG_FORTIFY_SOURCE:
>=20
> struct sha256_state {
>         u32 state[SHA256_DIGEST_SIZE / 4];
>         u64 count;
>         u8 buf[SHA256_BLOCK_SIZE];
> };
>=20
> This means that the memcpy() calls with "buf" as a destination in
> sha256.c's code will attempt to perform run-time bounds checking, which
> could lead to calling missing functions, specifically a potential
> WARN_ONCE, which isn't callable from purgatory.
>=20
> Reported-by: Thorsten Leemhuis <linux@leemhuis.info>
> Closes: https://lore.kernel.org/lkml/175578ec-9dec-7a9c-8d3a-43f24ff86b92=
@leemhuis.info/
> Bisected-by: "Joan Bruguera Mic=F3" <joanbrugueram@gmail.com>
> Fixes: df8fc4e934c1 ("kbuild: Enable -fstrict-flex-arrays=3D3")
> Cc: Paul Walmsley <paul.walmsley@sifive.com>
> Cc: Palmer Dabbelt <palmer@dabbelt.com>
> Cc: Albert Ou <aou@eecs.berkeley.edu>
> Cc: Masahiro Yamada <masahiroy@kernel.org>
> Cc: Conor Dooley <conor.dooley@microchip.com>

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>

Thanks for the quick update Kees,
Conor.

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