linux-kernel - Re: [PATCH] ubsan: disable unsigned-integer-overflow sanitizer with clang

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Date:   Tue, 5 Jan 2021 10:25:34 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Marco Elver <elver@...gle.com>, Kees Cook <keescook@...omium.org>,
        Arnd Bergmann <arnd@...db.de>,
        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 Mon, Jan 4, 2021 at 11:33 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
> On Wed, Dec 30, 2020 at 05:13:03PM +0100, Marco Elver wrote:
> > 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.
>
> This patch also fixes the failed BUILD_BUG issue in mm/mremap.c that you
> sent a patch for [1], along with a couple of other issues I see such as:

I'm fairly sure I still saw that BUILD_BUG() even after I had applied this
patch, I would guess that one just depends on inlining decisions that
are influenced by all kinds of compiler options including
-fsanitize=unsigned-integer-overflow, so it becomes less likely.

I'll revert my other patch in the randconfig tree to see if it comes back.

      Arnd