[PATCH] crypto: x86/aes-gcm-vaes-avx2 - initialize full %rax return register

[PATCH] crypto: x86/aes-gcm-vaes-avx2 - initialize full %rax return register

[Eric Biggers]

Update aes_gcm_dec_final_vaes_avx2() to be consistent with
aes_gcm_dec_final_aesni() and aes_gcm_dec_final_vaes_avx512() by
initializing the full %rax return register instead of just %al.
Technically this is unnecessary, since these functions return bool.  But
I think it's worth being extra careful with the result of the tag
comparison and also keeping the different implementations consistent.

Signed-off-by: Eric Biggers <ebiggers@kernel.org>
---

This patch is targeting libcrypto-next

 arch/x86/crypto/aes-gcm-vaes-avx2.S | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/crypto/aes-gcm-vaes-avx2.S b/arch/x86/crypto/aes-gcm-vaes-avx2.S
index d9754e683bde..93c9504a488f 100644
--- a/arch/x86/crypto/aes-gcm-vaes-avx2.S
+++ b/arch/x86/crypto/aes-gcm-vaes-avx2.S
@@ -1121,10 +1121,11 @@ SYM_FUNC_END(aes_gcm_aad_update_vaes_avx2)
 	vpxor		(%rax), GHASH_ACC, GHASH_ACC
 	vaesenclast	GHASH_ACC, %xmm0, %xmm0
 	lea		.Lselect_high_bytes_table(%rip), %rax
 	vmovdqu		(%rax, TAGLEN64), %xmm1
 	vpshufb		BSWAP_MASK, %xmm1, %xmm1 // select low bytes, not high
+	xor		%eax, %eax
 	vptest		%xmm1, %xmm0
 	sete		%al
 .endif
 	// No need for vzeroupper here, since only used xmm registers were used.
 	RET

base-commit: 5a2a5e62a5216ba05d4481cf90d915f4de0bfde9
-- 
2.51.2

Re: [PATCH] crypto: x86/aes-gcm-vaes-avx2 - initialize full %rax return register

[Ard Biesheuvel]

On Sun, 2 Nov 2025 at 02:53, Eric Biggers <ebiggers@kernel.org> wrote:
>
> Update aes_gcm_dec_final_vaes_avx2() to be consistent with
> aes_gcm_dec_final_aesni() and aes_gcm_dec_final_vaes_avx512() by
> initializing the full %rax return register instead of just %al.
> Technically this is unnecessary, since these functions return bool.  But
> I think it's worth being extra careful with the result of the tag
> comparison and also keeping the different implementations consistent.
>
> Signed-off-by: Eric Biggers <ebiggers@kernel.org>
> ---
>
> This patch is targeting libcrypto-next
>
>  arch/x86/crypto/aes-gcm-vaes-avx2.S | 1 +
>  1 file changed, 1 insertion(+)
>

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>

Re: [PATCH] crypto: x86/aes-gcm-vaes-avx2 - initialize full %rax return register

[Eric Biggers]

On Sat, Nov 01, 2025 at 06:52:56PM -0700, Eric Biggers wrote:
> Update aes_gcm_dec_final_vaes_avx2() to be consistent with
> aes_gcm_dec_final_aesni() and aes_gcm_dec_final_vaes_avx512() by
> initializing the full %rax return register instead of just %al.
> Technically this is unnecessary, since these functions return bool.  But
> I think it's worth being extra careful with the result of the tag
> comparison and also keeping the different implementations consistent.
> 
> Signed-off-by: Eric Biggers <ebiggers@kernel.org>
> ---
> 
> This patch is targeting libcrypto-next

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

- Eric