From: Matthew Garrett <matthew.garrett@nebula.com>
Date: Wed, 8 Nov 2017 15:11:32 +0000 (+0000)
Subject: kexec: Disable at runtime if the kernel is locked down
X-Git-Tag: archive/raspbian/4.18.10-2+rpi1^2~50
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=eb84ce0fd84767bee52acbe65b97cdb50fc1ad8c;p=linux.git

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

Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name 0006-kexec-Disable-at-runtime-if-the-kernel-is-locked-dow.patch
---

diff --git a/kernel/kexec.c b/kernel/kexec.c
index aed8fb2564b..1553ac765e7 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -199,6 +199,13 @@ static inline int kexec_load_check(unsigned long nr_segments,
 	if (!capable(CAP_SYS_BOOT) || kexec_load_disabled)
 		return -EPERM;
 
+	/*
+	 * 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.