Re: Build error in crypto/marvell/cesa/cipher.c

[Kees Cook <keescook@chromium.org>]

On Wed, Jun 28, 2023 at 08:13:25PM -0700, Linus Torvalds wrote:
> So I don't see anything that has changed, and I suspect the only
> change is that my compiler version changed, but my arm64 build fails
> right now with FORTIFY_STRING enabled.
> 
> On arm64 I now get this warning:
> 
>   In function 'fortify_memcpy_chk',
>     inlined from 'mv_cesa_des3_ede_setkey' and
> drivers/crypto/marvell/cesa/cipher.c:307:2:
>   ./include/linux/fortify-string.h:583:25: error: call to
> '__write_overflow_field' declared with attribute warning: detected
> write beyond size of field (1st parameter); maybe use struct_group()?
> [-Werror=attribute-warning[

This was fixed very recently here:
https://lore.kernel.org/all/20230523083313.899332-1-arnd@kernel.org/
and Herbert took it.

I assume the crypto tree hasn't been merged yet?

> Kees, any idea why I'm seeing it now? Is it the new
> -fstrict-flex-arrays=3? And if so, why? None of this is about flex
> arrays...

The unexpected bit is that without -fstrict-flex-arrays=3 (i.e. the
default since the dawn of time), the compiler treats any array that
happens to be the last struct member as a flexible array. So with it
enabled, FORTIFY_SOURCE gains coverage over things it should have been
examining before.

-- 
Kees Cook