Systems booted with shim have a Forbidden Signature Database called mokx.
During boot, hashes and certs contained within the mokx are loaded into the
blacklist keyring.  When calling verify_pkcs7_message_sig the contents of
the blacklist keyring (or revocation list) are referenced when validating
keys on the platform keyring. Currently, when validating against the
secondary or builtin keyrings, the revocation list is not referenced.  Move
up the check to allow the revocation list to be used with all keyrings,
including the secondary and builtin, allowing the system owner to take
corrective action should a vulnerability be found within keys contained
within either keyring.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>