Re: [PATCH] [v2] ubsan: disable unsigned-overflow check for i386

[Kees Cook <keescook@chromium.org>]

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