[PATCH 5.1 249/371] crypto: ccp/gcm - use const time tag comparison.

[Greg Kroah-Hartman]

From: Cfir Cohen <c...@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: <sta...@vger.kernel.org> # v4.12+
Signed-off-by: Cfir Cohen <c...@google.com>
Acked-by: Gary R Hook <gh...@amd.com>
Signed-off-by: Herbert Xu <herb...@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gre...@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);
        }