linux-kernel - [PATCH 06/30] kexec: Disable at runtime if the kernel is locked down

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Date:   Thu,  9 Nov 2017 17:31:23 +0000
From:   David Howells <dhowells@...hat.com>
To:     linux-security-module@...r.kernel.org
Cc:     gnomes@...rguk.ukuu.org.uk, linux-efi@...r.kernel.org,
        dhowells@...hat.com, linux-kernel@...r.kernel.org,
        jforbes@...hat.com
Subject: [PATCH 06/30] kexec: Disable at runtime if the kernel is locked down

From: Matthew Garrett <matthew.garrett@...ula.com>

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@...ula.com>
Signed-off-by: David Howells <dhowells@...hat.com>
Acked-by: Dave Young <dyoung@...hat.com>
Reviewed-by: "Lee, Chun-Yi" <jlee@...e.com>
Reviewed-by: James Morris <james.l.morris@...cle.com>
cc: kexec@...ts.infradead.org
---

 kernel/kexec.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/kexec.c b/kernel/kexec.c
index e62ec4dc6620..7dadfed9b676 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -202,6 +202,13 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
 		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.
 	 */