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

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Message-ID: <20190702155337.GA895@sol.localdomain>
Date:   Tue, 2 Jul 2019 08:53:37 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Gary R Hook <ghook@....com>
Cc:     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>,
        "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 Tue, Jul 02, 2019 at 03:41:23PM +0000, Gary R Hook wrote:
> 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?
> 

Herbert is the person who will apply this, so he'd need to do it.  But it might
be better just to resend.

- Eric