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Date:   Wed, 30 Dec 2020 17:13:03 +0100
From:   Marco Elver <elver@...gle.com>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>, Arnd Bergmann <arnd@...db.de>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        George Popescu <georgepope@...roid.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] ubsan: disable unsigned-integer-overflow sanitizer with clang

On Wed, 30 Dec 2020 at 16:47, Arnd Bergmann <arnd@...nel.org> wrote:
>
> From: Arnd Bergmann <arnd@...db.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.
>
> The one in blake2b immediately overflows the 8KB stack area on 32-bit
> architectures, so better ensure this never happens by making this
> option gcc-only.
>
> Fixes: d0a3ac549f38 ("ubsan: enable for all*config builds")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  lib/Kconfig.ubsan | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
> index 8b635fd75fe4..e23873282ba7 100644
> --- a/lib/Kconfig.ubsan
> +++ b/lib/Kconfig.ubsan
> @@ -122,6 +122,8 @@ config UBSAN_SIGNED_OVERFLOW
>
>  config UBSAN_UNSIGNED_OVERFLOW
>         bool "Perform checking for unsigned arithmetic overflow"
> +       # clang hugely expands stack usage with -fsanitize=object-size

This is the first time -fsanitize=object-size is mentioned. Typo?

> +       depends on !CC_IS_CLANG
>         depends on $(cc-option,-fsanitize=unsigned-integer-overflow)
>         help
>           This option enables -fsanitize=unsigned-integer-overflow which checks
> --
> 2.29.2
>

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