linux-kernel - [PATCH 05/27] kexec_load: Disable at runtime if the kernel is locked down

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Message-Id: <20190228231203.212359-5-matthewgarrett@google.com>
Date:   Thu, 28 Feb 2019 15:11:41 -0800
From:   Matthew Garrett <matthewgarrett@...gle.com>
To:     jmorris@...ei.org
Cc:     linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, dhowells@...hat.com
Subject: [PATCH 05/27] kexec_load: Disable at runtime if the kernel is locked down

From: Matthew Garrett <mjg59@...f.ucam.org>

The kexec_load() syscall 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_load() in this situation.

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

Signed-off-by: Matthew Garrett <mjg59@...f.ucam.org>
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 68559808fdfa..8ea0ce31271f 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -207,6 +207,13 @@ static inline int kexec_load_check(unsigned long nr_segments,
 	if (result < 0)
 		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.
-- 
2.21.0.352.gf09ad66450-goog