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

[Nathan Chancellor <natechancellor@gmail.com>]

On Wed, Jan 06, 2021 at 10:12:51AM +0100, Arnd Bergmann wrote:
> On Tue, Jan 5, 2021 at 10:25 AM Arnd Bergmann <arnd@kernel.org> wrote:
> >
> > On Mon, Jan 4, 2021 at 11:33 PM Nathan Chancellor
> > <natechancellor@gmail.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@kernel.org> 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.
> > > > >
> > > > > 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.
> 
> The qcom/gpi.c failure still happens with this patch applied:
> 
> In file included from /git/arm-soc/drivers/dma/qcom/gpi.c:8:
> In function 'field_multiplier',
>     inlined from 'gpi_update_reg' at
> /git/arm-soc/include/linux/bitfield.h:124:17:
> /git/arm-soc/include/linux/bitfield.h:119:3: error: call to
> '__bad_mask' declared with attribute error: bad bitfield mask
>   119 |   __bad_mask();
>       |   ^~~~~~~~~~~~
> In function 'field_multiplier',
>     inlined from 'gpi_update_reg' at
> /git/arm-soc/include/linux/bitfield.h:154:1:
> /git/arm-soc/include/linux/bitfield.h:119:3: error: call to
> '__bad_mask' declared with attribute error: bad bitfield mask
>   119 |   __bad_mask();
>       |   ^~~~~~~~~~~~
> 
> See https://pastebin.com/8UH6x4A2 for the .config
> 
>        Arnd

That config does not build for me, am I holding it wrong?

$ curl -LSso .config https://pastebin.com/raw/8UH6x4A2

$ make -skj"$(nproc)" ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- LLVM=1 olddefconfig vmlinux
.config:364:warning: override: ARCH_DOVE changes choice state
arch/arm/kernel/sys_oabi-compat.c:257:6: error: implicit declaration of function 'ep_op_has_event' [-Werror,-Wimplicit-function-declaration]
        if (ep_op_has_event(op) &&
            ^
arch/arm/kernel/sys_oabi-compat.c:264:9: error: implicit declaration of function 'do_epoll_ctl' [-Werror,-Wimplicit-function-declaration]
        return do_epoll_ctl(epfd, op, fd, &kernel, false);
               ^
arch/arm/kernel/sys_oabi-compat.c:264:9: note: did you mean 'sys_epoll_ctl'?
./include/linux/syscalls.h:359:17: note: 'sys_epoll_ctl' declared here
asmlinkage long sys_epoll_ctl(int epfd, int op, int fd,
                ^
2 errors generated.
...

Cheers,
Nathan