linux-kernel - Re: [PATCH v2] lib/crypto: curve25519-hacl64: Fix older clang KASAN workaround for GCC

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Message-ID: <20251104173840.GB1780@sol>
Date: Tue, 4 Nov 2025 09:38:40 -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 v2] lib/crypto: curve25519-hacl64: Fix older clang KASAN
 workaround for GCC

On Mon, Nov 03, 2025 at 12:11:24PM -0700, 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_CLANG to avoid applying
> the workaround for GCC, which is only needed for clang-17 and older.
> 
> 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>
> ---
> Changes in v2:
> - Check for CONFIG_CC_IS_CLANG explicitly instead of using
>   CONFIG_CC_IS_GCC as "not clang" (Eric).
> - Link to v1: https://patch.msgid.link/20251102-curve25519-hacl64-fix-kasan-workaround-v1-1-6ec6738f9741@kernel.org
> ---
>  lib/crypto/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/crypto/Makefile b/lib/crypto/Makefile
> index bded351aeace..d2845b214585 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),)
> +ifeq ($(CONFIG_CC_IS_CLANG)_$(call clang-min-version, 180000),y_)
>  KASAN_SANITIZE_curve25519-hacl64.o := n
>  endif

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux.git/log/?h=libcrypto-fixes

- Eric