linux-kernel - Re: [PATCH v2] riscv/purgatory: Do not use fortified string functions

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Message-ID: <20230601-connected-unbolted-cf708c6da4a1@spud>
Date:   Thu, 1 Jun 2023 18:34:20 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Thorsten Leemhuis <linux@...mhuis.info>,
        Joan Bruguera Micó <joanbrugueram@...il.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Alyssa Ross <hi@...ssa.is>,
        Heiko Stuebner <heiko.stuebner@...ll.eu>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-riscv@...ts.infradead.org,
        Andrew Jones <ajones@...tanamicro.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] riscv/purgatory: Do not use fortified string functions

On Thu, Jun 01, 2023 at 09:00:28AM -0700, Kees Cook wrote:
> With the addition of -fstrict-flex-arrays=3, struct sha256_state's
> trailing array is no longer ignored by CONFIG_FORTIFY_SOURCE:
> 
> struct sha256_state {
>         u32 state[SHA256_DIGEST_SIZE / 4];
>         u64 count;
>         u8 buf[SHA256_BLOCK_SIZE];
> };
> 
> 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.
> 
> Reported-by: Thorsten Leemhuis <linux@...mhuis.info>
> Closes: https://lore.kernel.org/lkml/175578ec-9dec-7a9c-8d3a-43f24ff86b92@leemhuis.info/
> Bisected-by: "Joan Bruguera Micó" <joanbrugueram@...il.com>
> Fixes: df8fc4e934c1 ("kbuild: Enable -fstrict-flex-arrays=3")
> Cc: Paul Walmsley <paul.walmsley@...ive.com>
> Cc: Palmer Dabbelt <palmer@...belt.com>
> Cc: Albert Ou <aou@...s.berkeley.edu>
> Cc: Masahiro Yamada <masahiroy@...nel.org>
> Cc: Conor Dooley <conor.dooley@...rochip.com>

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

Thanks for the quick update Kees,
Conor.

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