linux-kernel - Re: [PATCH] crypto: arm64/ghash - Fix incorrect output from ghash-neon

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Message-Id: <DEUFDH7FJURL.3J0FN5I19VV8F@cknow-tech.com>
Date: Wed, 10 Dec 2025 10:22:19 +0100
From: "Diederik de Haas" <diederik@...ow-tech.com>
To: "Eric Biggers" <ebiggers@...nel.org>, <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-arm-kernel@...ts.infradead.org>,
 <stable@...r.kernel.org>, "Diederik de Haas" <diederik@...ow-tech.com>
Subject: Re: [PATCH] crypto: arm64/ghash - Fix incorrect output from
 ghash-neon

On Tue Dec 9, 2025 at 11:34 PM CET, Eric Biggers wrote:
> Commit 9a7c987fb92b ("crypto: arm64/ghash - Use API partial block
> handling") made ghash_finup() pass the wrong buffer to
> ghash_do_simd_update().  As a result, ghash-neon now produces incorrect
> outputs when the message length isn't divisible by 16 bytes.  Fix this.

I was hoping to not have to do a 'git bisect', but this is much better
:-D I can confirm that this patch fixes the error I was seeing, so

Tested-by: Diederik de Haas <diederik@...ow-tech.com>

> (I didn't notice this earlier because this code is reached only on CPUs
> that support NEON but not PMULL.  I haven't yet found a way to get
> qemu-system-aarch64 to emulate that configuration.)

https://www.qemu.org/docs/master/system/arm/raspi.html indicates it can
emulate various Raspberry Pi models. I've only tested it with RPi 3B+
(bc of its wifi+bt chip), but I wouldn't be surprised if all RPi models
would have this problem? Dunno if QEMU emulates that though.

Thanks for the quick fix!

Cheers,
  Diederik

> Fixes: 9a7c987fb92b ("crypto: arm64/ghash - Use API partial block handling")
> Cc: stable@...r.kernel.org
> Reported-by: Diederik de Haas <diederik@...ow-tech.com>
> Closes: https://lore.kernel.org/linux-crypto/DETXT7QI62KE.F3CGH2VWX1SC@cknow-tech.com/
> Signed-off-by: Eric Biggers <ebiggers@...nel.org>
> ---
>
> If it's okay, I'd like to just take this via libcrypto-fixes.
>
>  arch/arm64/crypto/ghash-ce-glue.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/crypto/ghash-ce-glue.c b/arch/arm64/crypto/ghash-ce-glue.c
> index 7951557a285a..ef249d06c92c 100644
> --- a/arch/arm64/crypto/ghash-ce-glue.c
> +++ b/arch/arm64/crypto/ghash-ce-glue.c
> @@ -131,11 +131,11 @@ static int ghash_finup(struct shash_desc *desc, const u8 *src,
>  
>  	if (len) {
>  		u8 buf[GHASH_BLOCK_SIZE] = {};
>  
>  		memcpy(buf, src, len);
> -		ghash_do_simd_update(1, ctx->digest, src, key, NULL,
> +		ghash_do_simd_update(1, ctx->digest, buf, key, NULL,
>  				     pmull_ghash_update_p8);
>  		memzero_explicit(buf, sizeof(buf));
>  	}
>  	return ghash_export(desc, dst);
>  }
>
> base-commit: 7a3984bbd69055898add0fe22445f99435f33450