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

[Cfir Cohen]

Avoid leaking GCM tag through timing side channel.

Fixes: 36cf515b9bbe ("crypto: ccp - Enable support for AES GCM on v5 CCPs")
Cc: <sta...@vger.kernel.org> # v4.12+
Signed-off-by: Cfir Cohen <c...@google.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