linux-kernel - Re: [PATCH 0/6] lib/crypto: More at

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Message-ID: <20251123040037.GA42791@sol>
Date: Sat, 22 Nov 2025 20:00:37 -0800
From: Eric Biggers <ebiggers@...nel.org>
To: linux-crypto@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
	"Jason A . Donenfeld" <Jason@...c4.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	linux-hardening@...r.kernel.org, Kees Cook <kees@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 0/6] lib/crypto: More at_least decorations

On Sat, Nov 22, 2025 at 11:42:00AM -0800, Eric Biggers wrote:
> This series depends on the 'at_least' macro added by
> https://lore.kernel.org/r/20251122025510.1625066-4-Jason@zx2c4.com
> It can also be retrieved from
> 
>     git fetch https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git more-at-least-decorations-v1
> 
> Add the at_least (i.e. 'static') decoration to the fixed-size array
> parameters of more of the crypto library functions.  This causes clang
> to generate a warning if a too-small array of known size is passed.
> 
> Eric Biggers (6):
>   lib/crypto: chacha: Add at_least decoration to fixed-size array params
>   lib/crypto: curve25519: Add at_least decoration to fixed-size array
>     params
>   lib/crypto: md5: Add at_least decoration to fixed-size array params
>   lib/crypto: poly1305: Add at_least decoration to fixed-size array
>     params
>   lib/crypto: sha1: Add at_least decoration to fixed-size array params
>   lib/crypto: sha2: Add at_least decoration to fixed-size array params
> 
>  include/crypto/chacha.h     | 12 ++++-----
>  include/crypto/curve25519.h | 24 ++++++++++-------
>  include/crypto/md5.h        | 11 ++++----
>  include/crypto/poly1305.h   |  2 +-
>  include/crypto/sha1.h       | 12 +++++----
>  include/crypto/sha2.h       | 53 ++++++++++++++++++++++---------------

It turns out this causes a build error when <crypto/poly1305.h>,
<crypto/sha1.h>, or <crypto/sha2.h> is included before
<linux/compiler.h>.

Jason's patch to <crypto/chacha20poly1305.h> is okay, because that one
indirectly includes <linux/compiler.h> by chance.

I thought <linux/compiler.h> already got included in everything via the
-include compiler flag.  But it's actually <linux/compiler_types.h>
which works that way, not <linux/compiler.h> which is a regular header.

We can make these crypto headers include <linux/compiler.h>.  But before
we do that, should we perhaps consider putting the definition of
'at_least' in <linux/compiler_types.h> instead of in <linux/compiler.h>,
so that it becomes always available?  This is basically a core language
feature.  Maybe it belongs next to the definition of __counted_by, which
is another definition related to array bounds?

- Eric