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Date:   Wed, 28 Jun 2023 20:48:19 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Boris Brezillon <bbrezillon@kernel.org>,
        Arnaud Ebalard <arno@natisbad.org>,
        Srujana Challa <schalla@marvell.com>,
        Mustafa Ismail <mustafa.ismail@intel.com>,
        Shiraz Saleem <shiraz.saleem@intel.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Leon Romanovsky <leon@kernel.org>
Subject: Re: Build error in crypto/marvell/cesa/cipher.c
Message-ID: <202306282038.C3A12326A@keescook>
References: <CAHk-=whXn0YTojV=+J8B-r8KLvNtqc2JtCa4a_bdhf+=GN5OOw@mail.gmail.com>
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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