From: Matthew Garrett <matthew.garrett@nebula.com>
Date: Wed, 8 Nov 2017 15:11:32 +0000
Subject: [06/29] kexec: Disable at runtime if the kernel is locked down
Origin: https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/commit?id=6081db9ba435b757a3a3473d0cd50ee2252ccaeb

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
[bwh: Adjust context to apply after commit a210fd32a46b
 "kexec: add call to LSM hook in original kexec_load syscall"]
---
 kernel/kexec.c | 7 +++++++
 1 file changed, 7 insertions(+)

Index: linux/kernel/kexec.c
===================================================================
--- linux.orig/kernel/kexec.c
+++ linux/kernel/kexec.c
@@ -208,6 +208,13 @@ static inline int kexec_load_check(unsig
 		return result;
 
 	/*
+	 * kexec can be used to circumvent module loading restrictions, so
+	 * prevent loading in that case
+	 */
+	if (kernel_is_locked_down("kexec of unsigned images"))
+		return -EPERM;
+
+	/*
 	 * Verify we have a legal set of flags
 	 * This leaves us room for future extensions.
 	 */
