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

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Message-ID: <20230531-abruptly-settling-f9852f408dcd@spud>
Date:   Wed, 31 May 2023 23:37:20 +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, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] riscv/purgatory: Do not use fortified string functions

Hey Kees,

On Tue, May 30, 2023 at 05:34:04PM -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>
> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> Cc: Alyssa Ross <hi@...ssa.is>
> Cc: Heiko Stuebner <heiko.stuebner@...ll.eu>
> Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> Cc: linux-riscv@...ts.infradead.org
> Signed-off-by: Kees Cook <keescook@...omium.org>

Perhaps this is indicative of other issues in RISC-V land, but
allmodconfig complains about this patch:

../lib/string.c:17: warning: "__NO_FORTIFY" redefined
../lib/string.c:17:9: warning: preprocessor token __NO_FORTIFY redefined

> ---
>  arch/riscv/purgatory/Makefile | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/riscv/purgatory/Makefile b/arch/riscv/purgatory/Makefile
> index 5730797a6b40..11f4c275f141 100644
> --- a/arch/riscv/purgatory/Makefile
> +++ b/arch/riscv/purgatory/Makefile
> @@ -31,9 +31,9 @@ $(obj)/strncmp.o: $(srctree)/arch/riscv/lib/strncmp.S FORCE
>  $(obj)/sha256.o: $(srctree)/lib/crypto/sha256.c FORCE
>  	$(call if_changed_rule,cc_o_c)
>  
> -CFLAGS_sha256.o := -D__DISABLE_EXPORTS
> -CFLAGS_string.o := -D__DISABLE_EXPORTS
> -CFLAGS_ctype.o := -D__DISABLE_EXPORTS
> +CFLAGS_sha256.o := -D__DISABLE_EXPORTS -D__NO_FORTIFY
> +CFLAGS_string.o := -D__DISABLE_EXPORTS -D__NO_FORTIFY
> +CFLAGS_ctype.o := -D__DISABLE_EXPORTS -D__NO_FORTIFY
>  
>  # When linking purgatory.ro with -r unresolved symbols are not checked,
>  # also link a purgatory.chk binary without -r to check for unresolved symbols.
> -- 
> 2.34.1
> 
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

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