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Date:   Tue, 12 Jan 2021 17:05:55 -0700
From:   Nathan Chancellor <natechancellor@gmail.com>
To:     Arnd Bergmann <arnd@kernel.org>
Cc:     Nick Desaulniers <ndesaulniers@google.com>,
        Kees Cook <keescook@chromium.org>,
        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: <20210113000555.GA1584947@ubuntu-m3-large-x86>
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>

Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>

> ---
> v2: only turn it off for i386 as discussed
> ---
>  lib/Kconfig.ubsan | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
> index 8b635fd75fe4..3a0b1c930733 100644
> --- a/lib/Kconfig.ubsan
> +++ b/lib/Kconfig.ubsan
> @@ -123,6 +123,7 @@ config UBSAN_SIGNED_OVERFLOW
>  config UBSAN_UNSIGNED_OVERFLOW
>  	bool "Perform checking for unsigned arithmetic overflow"
>  	depends on $(cc-option,-fsanitize=unsigned-integer-overflow)
> +	depends on !X86_32 # avoid excessive stack usage on x86-32/clang
>  	help
>  	  This option enables -fsanitize=unsigned-integer-overflow which checks
>  	  for overflow of any arithmetic operations with unsigned integers. This
> -- 
> 2.29.2
>