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Date:   Tue, 12 Jan 2021 15:53:51 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Arnd Bergmann <arnd@kernel.org>
Cc:     Nathan Chancellor <natechancellor@gmail.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Andrew Morton <akpm@linux-foundation.org>,
        Arnd Bergmann <arnd@arndb.de>, Marco Elver <elver@google.com>,
        George Popescu <georgepope@android.com>,
        linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com
Subject: Re: [PATCH] [v2] ubsan: disable unsigned-overflow check for i386
Message-ID: <202101121553.D0C3B87D5@keescook>
References: <20210112202922.2454435-1-arnd@kernel.org>
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On Tue, Jan 12, 2021 at 09:29:15PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> Building ubsan kernels even for compile-testing introduced these
> warnings in my randconfig environment:
> 
> crypto/blake2b_generic.c:98:13: error: stack frame size of 9636 bytes in function 'blake2b_compress' [-Werror,-Wframe-larger-than=]
> static void blake2b_compress(struct blake2b_state *S,
> crypto/sha512_generic.c:151:13: error: stack frame size of 1292 bytes in function 'sha512_generic_block_fn' [-Werror,-Wframe-larger-than=]
> static void sha512_generic_block_fn(struct sha512_state *sst, u8 const *src,
> lib/crypto/curve25519-fiat32.c:312:22: error: stack frame size of 2180 bytes in function 'fe_mul_impl' [-Werror,-Wframe-larger-than=]
> static noinline void fe_mul_impl(u32 out[10], const u32 in1[10], const u32 in2[10])
> lib/crypto/curve25519-fiat32.c:444:22: error: stack frame size of 1588 bytes in function 'fe_sqr_impl' [-Werror,-Wframe-larger-than=]
> static noinline void fe_sqr_impl(u32 out[10], const u32 in1[10])
> 
> Further testing showed that this is caused by
> -fsanitize=unsigned-integer-overflow, but is isolated to the 32-bit
> x86 architecture.
> 
> The one in blake2b immediately overflows the 8KB stack area architectures,
> so better ensure this never happens by disabling the option for 32-bit
> x86.
> 
> Fixes: d0a3ac549f38 ("ubsan: enable for all*config builds")
> Link: https://lore.kernel.org/lkml/20201230154749.746641-1-arnd@kernel.org/
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Acked-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook