UBUNTU: SAUCE: (efi-lockdown) kexec: Disable at runtime if the kernel is locked down

UBUNTU: SAUCE: (efi-lockdown) kexec: Disable at runtime if the kernel is locked down

kexec permits the loading and execution of arbitrary code in ring 0, which
is something that lock-down is meant to prevent. It makes sense to disable
kexec in this situation.

This does not affect kexec_file_load() which can check for a signature on the
image to be booted.

Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Dave Young <dyoung@redhat.com>
Reviewed-by: "Lee, Chun-Yi" <jlee@suse.com>
Reviewed-by: James Morris <james.l.morris@oracle.com>
cc: kexec@lists.infradead.org
(cherry picked from commit 9a7ef0aead9519d42e351d10e0c6f7b8d3bebdb1
 git://git.kernel.org/pub/scm/linux/kernel/git/jwboyer/fedora.git)
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>