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

[Gary R Hook]

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@xxxxxxxxxxxxxxx> # v4.12+
> Signed-off-by: Cfir Cohen <cfir@xxxxxxxxxx>

Acked-by: Gary R Hook <ghook@xxxxxxx>

> ---
>   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);
>   	}
>   
>