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

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Message-ID: <1eea04e4-ac19-241d-695b-61be43640509@amd.com>
Date:   Tue, 2 Jul 2019 15:41:23 +0000
From:   Gary R Hook <ghook@....com>
To:     Eric Biggers <ebiggers@...nel.org>, Cfir Cohen <cfir@...gle.com>
CC:     "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        "Hook, Gary" <Gary.Hook@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        David Rientjes <rientjes@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>
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 <cfir@...gle.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);
>>   	}
>>   
>> -- 
>> 2.22.0.410.gd8fdbe21b5-goog
>>
> 
> Looks like this needs:
> 
> 	Fixes: 36cf515b9bbe ("crypto: ccp - Enable support for AES GCM on v5 CCPs")
> 	Cc: <stable@...r.kernel.org> # v4.12+


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