linux-kernel - Re: [PATCH] lib/crypto: curve25519-hacl64: Fix older clang KASAN workaround for GCC

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Message-ID: <20251103170036.GD1735@sol>
Date: Mon, 3 Nov 2025 09:00:36 -0800
From: Eric Biggers <ebiggers@...nel.org>
To: Nathan Chancellor <nathan@...nel.org>
Cc: "Jason A. Donenfeld" <Jason@...c4.com>,
	Ard Biesheuvel <ardb@...nel.org>, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] lib/crypto: curve25519-hacl64: Fix older clang KASAN
 workaround for GCC

On Sun, Nov 02, 2025 at 09:35:03PM -0500, Nathan Chancellor wrote:
> Commit 2f13daee2a72 ("lib/crypto/curve25519-hacl64: Disable KASAN with
> clang-17 and older") inadvertently disabled KASAN in curve25519-hacl64.o
> for GCC unconditionally because clang-min-version will always evaluate
> to nothing for GCC. Add a check for CONFIG_CC_IS_GCC to avoid the
> workaround, which is only needed for clang-17 and older.
> 
> Additionally, invert the 'ifeq (...,)' into 'ifneq (...,y)', as it is a
> little easier to read and understand the intention ("if not GCC or at
> least clang-18, disable KASAN").
> 
> Cc: stable@...r.kernel.org
> Fixes: 2f13daee2a72 ("lib/crypto/curve25519-hacl64: Disable KASAN with clang-17 and older")
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
>  lib/crypto/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/crypto/Makefile b/lib/crypto/Makefile
> index bded351aeace..372b7a12b371 100644
> --- a/lib/crypto/Makefile
> +++ b/lib/crypto/Makefile
> @@ -90,7 +90,7 @@ else
>  libcurve25519-$(CONFIG_CRYPTO_LIB_CURVE25519_GENERIC) += curve25519-fiat32.o
>  endif
>  # clang versions prior to 18 may blow out the stack with KASAN
> -ifeq ($(call clang-min-version, 180000),)
> +ifneq ($(CONFIG_CC_IS_GCC)$(call clang-min-version, 180000),y)
>  KASAN_SANITIZE_curve25519-hacl64.o := n
>  endif

Thanks for catching this!

Using CONFIG_CC_IS_GCC == "" to check for clang seems a bit odd when
there's already a CONFIG_CC_IS_CLANG available.

How about we do it like this?

    ifeq ($(CONFIG_CC_IS_CLANG)_$(call clang-min-version, 180000),y_)

- Eric