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From:   Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date:   Tue, 28 May 2019 16:36:25 +0200
Message-ID: <CAKv+Gu9+79HV3EvTGpqJS8nCbfZ22xtvUbJ5XyMuuF9bR+Nysw@mail.gmail.com>
Subject: Re: [PATCH] arm64 sha2-ce finup: correct digest for empty data
To:     Elena Petrova <lenaptr@google.com>
Cc:     "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@vger.kernel.org>, stable <stable@vger.kernel.org>
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On Tue, 28 May 2019 at 16:35, Elena Petrova <lenaptr@google.com> wrote:
>
> The sha256-ce finup implementation for ARM64 produces wrong digest
> for empty input (len=0). Expected: the actual digest, result: initial
> value of SHA internal state. The error is in sha256_ce_finup:
> for empty data `finalize` will be 1, so the code is relying on
> sha2_ce_transform to make the final round. However, in
> sha256_base_do_update, the block function will not be called when
> len == 0.
>
> Fix it by setting finalize to 0 if data is empty.
>
> Fixes: 03802f6a80b3a ("crypto: arm64/sha2-ce - move SHA-224/256 ARMv8 implementation to base layer")
> Cc: stable@vger.kernel.org
> Signed-off-by: Elena Petrova <lenaptr@google.com>

Thanks again

Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

> ---
>  arch/arm64/crypto/sha2-ce-glue.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/crypto/sha2-ce-glue.c b/arch/arm64/crypto/sha2-ce-glue.c
> index a725997e55f2..6a5ade974a35 100644
> --- a/arch/arm64/crypto/sha2-ce-glue.c
> +++ b/arch/arm64/crypto/sha2-ce-glue.c
> @@ -60,7 +60,7 @@ static int sha256_ce_finup(struct shash_desc *desc, const u8 *data,
>                            unsigned int len, u8 *out)
>  {
>         struct sha256_ce_state *sctx = shash_desc_ctx(desc);
> -       bool finalize = !sctx->sst.count && !(len % SHA256_BLOCK_SIZE);
> +       bool finalize = !sctx->sst.count && !(len % SHA256_BLOCK_SIZE) && len;
>
>         if (!crypto_simd_usable()) {
>                 if (len)
> --
> 2.22.0.rc1.257.g3120a18244-goog
>