linux-kernel - Re: [PATCH v2] crypto: ccp/gcm - use const time tag comparison.

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Date:   Tue, 2 Jul 2019 17:46:53 +0000
From:   Gary R Hook <ghook@....com>
To:     Cfir Cohen <cfir@...gle.com>,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        "Hook, Gary" <Gary.Hook@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        David Rientjes <rientjes@...gle.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v2] crypto: ccp/gcm - use const time tag comparison.

On 7/2/19 12:32 PM, Cfir Cohen wrote:
> Avoid leaking GCM tag through timing side channel.
> 
> Fixes: 36cf515b9bbe ("crypto: ccp - Enable support for AES GCM on v5 CCPs")
> Cc: <stable@...r.kernel.org> # v4.12+
> Signed-off-by: Cfir Cohen <cfir@...gle.com>

Acked-by: Gary R Hook <ghook@....com>

> ---
>   drivers/crypto/ccp/ccp-ops.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/crypto/ccp/ccp-ops.c b/drivers/crypto/ccp/ccp-ops.c
> index db8de89d990f..633670220f6c 100644
> --- a/drivers/crypto/ccp/ccp-ops.c
> +++ b/drivers/crypto/ccp/ccp-ops.c
> @@ -840,7 +840,8 @@ static int ccp_run_aes_gcm_cmd(struct ccp_cmd_queue *cmd_q,
>   		if (ret)
>   			goto e_tag;
>   
> -		ret = memcmp(tag.address, final_wa.address, AES_BLOCK_SIZE);
> +		ret = crypto_memneq(tag.address, final_wa.address,
> +				    AES_BLOCK_SIZE) ? -EBADMSG : 0;
>   		ccp_dm_free(&tag);
>   	}
>   
>