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    Subject[PATCH 4.19 181/271] crypto: ccp/gcm - use const time tag comparison.
    Date
    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);
    }


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