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

[Nathan Chancellor]

On Wed, Dec 30, 2020 at 05:13:03PM +0100, Marco Elver wrote:
> On Wed, 30 Dec 2020 at 16:47, Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
> >
> > From: Arnd Bergmann <arnd@xxxxxxxx>
> >
> > 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:

ld.lld: error: undefined symbol: __bad_mask
>>> referenced by gpi.c
>>>               dma/qcom/gpi.o:(gpi_update_reg) in archive
>>>               drivers/built-in.a
>>> referenced by gpi.c
>>>               dma/qcom/gpi.o:(gpi_update_reg) in archive
>>>               drivers/built-in.a

[1]: https://lore.kernel.org/lkml/20201230154104.522605-1-arnd@xxxxxxxxxx/

Reviewed-by: Nathan Chancellor <natechancellor@xxxxxxxxx>

> > Fixes: d0a3ac549f38 ("ubsan: enable for all*config builds")
> > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> > ---
> >  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?

Copy and paste issue from CONFIG_UBSAN_OBJECT_SIZE

> > +       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
> >