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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Cfir Cohen <cfir@google.com>,
        Gary R Hook <ghook@amd.com>,
        Herbert Xu <herbert@gondor.apana.org.au>
Subject: [PATCH 4.19 181/271] crypto: ccp/gcm - use const time tag comparison.
Date:   Wed, 24 Jul 2019 21:20:50 +0200
Message-Id: <20190724191710.650102308@linuxfoundation.org>
In-Reply-To: <20190724191655.268628197@linuxfoundation.org>
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From: Cfir Cohen <cfir@google.com>

commit 538a5a072e6ef04377b180ee9b3ce5bae0a85da4 upstream.

Avoid leaking GCM tag through timing side channel.

Fixes: 36cf515b9bbe ("crypto: ccp - Enable support for AES GCM on v5 CCPs")
Cc: <stable@vger.kernel.org> # v4.12+
Signed-off-by: Cfir Cohen <cfir@google.com>
Acked-by: Gary R Hook <ghook@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/crypto/ccp/ccp-ops.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/crypto/ccp/ccp-ops.c
+++ b/drivers/crypto/ccp/ccp-ops.c
@@ -853,7 +853,8 @@ static int ccp_run_aes_gcm_cmd(struct cc
 		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);
 	}