UBUNTU: SAUCE: (efi-lockdown) MODSIGN: Import certificates from UEFI Secure Boot

UBUNTU: SAUCE: (efi-lockdown) MODSIGN: Import certificates from UEFI Secure Boot

Secure Boot stores a list of allowed certificates in the 'db' variable.
This imports those certificates into the system trusted keyring.  This
allows for a third party signing certificate to be used in conjunction
with signed modules.  By importing the public certificate into the 'db'
variable, a user can allow a module signed with that certificate to
load.  The shim UEFI bootloader has a similar certificate list stored
in the 'MokListRT' variable.  We import those as well.

Secure Boot also maintains a list of disallowed certificates in the 'dbx'
variable.  We load those certificates into the newly introduced system
blacklist keyring and forbid any module signed with those from loading and
forbid the use within the kernel of any key with a matching hash.

This facility is enabled by setting CONFIG_LOAD_UEFI_KEYS.

Signed-off-by: Josh Boyer <jwboyer@fedoraproject.org>
Signed-off-by: David Howells <dhowells@redhat.com>
(cherry picked from commit dc5fd3fc2faf24eed23ed8317f2315fb49ff6382
 git://git.kernel.org/pub/scm/linux/kernel/git/jwboyer/fedora.git)
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>