2019-07-02 00:25:50

by Eric Biggers

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

On Mon, Jul 01, 2019 at 05:01:32PM -0700, Cfir Cohen wrote:
> Avoid leaking GCM tag through timing side channel.
>
> Signed-off-by: Cfir Cohen <[email protected]>
> ---
> 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);
> }
>
> --
> 2.22.0.410.gd8fdbe21b5-goog
>

Looks like this needs:

Fixes: 36cf515b9bbe ("crypto: ccp - Enable support for AES GCM on v5 CCPs")
Cc: <[email protected]> # v4.12+

- Eric

2019-07-02 15:41:50

by Gary R Hook

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

On 7/1/19 7:25 PM, Eric Biggers wrote:
> On Mon, Jul 01, 2019 at 05:01:32PM -0700, Cfir Cohen wrote:
>> Avoid leaking GCM tag through timing side channel.
>>
>> Signed-off-by: Cfir Cohen <[email protected]>
>> ---
>> 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);
>> }
>>
>> --
>> 2.22.0.410.gd8fdbe21b5-goog
>>
>
> Looks like this needs:
>
> Fixes: 36cf515b9bbe ("crypto: ccp - Enable support for AES GCM on v5 CCPs")
> Cc: <[email protected]> # v4.12+


Yes, it does. For clarity, does that mean you've taken care of this?