[PATCH] lib/crypto: arm/curve25519: Disable on CPU_BIG_ENDIAN

[Ard Biesheuvel]

On Tue, 4 Nov 2025 at 06:51, Eric Biggers <ebiggers at kernel.org> wrote:
>
> On big endian arm kernels, the arm optimized Curve25519 code produces
> incorrect outputs and fails the Curve25519 test.  This has been true
> ever since this code was added.
>
> It seems that hardly anyone (or even no one?) actually uses big endian
> arm kernels.  But as long as they're ostensibly supported, we should
> disable this code on them so that it's not accidentally used.
>
> Note: for future-proofing, use !CPU_BIG_ENDIAN instead of
> CPU_LITTLE_ENDIAN.  Both of these are arch-specific options that could
> get removed in the future if big endian support gets dropped.
>
> Fixes: d8f1308a025f ("crypto: arm/curve25519 - wire up NEON implementation")
> Cc: stable at vger.kernel.org
> Signed-off-by: Eric Biggers <ebiggers at kernel.org>
> ---
>
> This patch is targeting libcrypto-fixes
>
>  lib/crypto/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>

Acked-by: Ard Biesheuvel <ardb at kernel.org>

> diff --git a/lib/crypto/Kconfig b/lib/crypto/Kconfig
> index 8886055e938f..16859c6226dd 100644
> --- a/lib/crypto/Kconfig
> +++ b/lib/crypto/Kconfig
> @@ -62,11 +62,11 @@ config CRYPTO_LIB_CURVE25519
>           of the functions from <crypto/curve25519.h>.
>
>  config CRYPTO_LIB_CURVE25519_ARCH
>         bool
>         depends on CRYPTO_LIB_CURVE25519 && !UML && !KMSAN
> -       default y if ARM && KERNEL_MODE_NEON
> +       default y if ARM && KERNEL_MODE_NEON && !CPU_BIG_ENDIAN
>         default y if PPC64 && CPU_LITTLE_ENDIAN
>         default y if X86_64
>
>  config CRYPTO_LIB_CURVE25519_GENERIC
>         bool
>
> base-commit: 1af424b15401d2be789c4dc2279889514e7c5c94
> --
> 2.51.2
>