linux-kernel - [PATCH 08/12] kexec: Disable loading of unverified images

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Date:	Fri, 13 Mar 2015 11:38:24 -1000
From:	Matthew Garrett <matthew.garrett@...ula.com>
To:	linux-security-module@...r.kernel.org
Cc:	james.l.morris@...cle.com, serge@...lyn.com,
	linux-kernel@...r.kernel.org, keescook@...omium.org, hpa@...or.com,
	gnomes@...rguk.ukuu.org.uk,
	Matthew Garrett <matthew.garrett@...ula.com>
Subject: [PATCH 08/12] kexec: Disable loading of unverified images

kexec permits the loading and execution of arbitrary code in ring 0, which
permits the modification of the running kernel. Restrict it such that only
images which have been verified may be loaded when trusted_kernel is true.

Signed-off-by: Matthew Garrett <matthew.garrett@...ula.com>
---
 kernel/kexec.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/kernel/kexec.c b/kernel/kexec.c
index 38c25b1..463b369 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -36,6 +36,7 @@
 #include <linux/syscore_ops.h>
 #include <linux/compiler.h>
 #include <linux/hugetlb.h>
+#include <linux/security.h>
 
 #include <asm/page.h>
 #include <asm/uaccess.h>
@@ -1247,6 +1248,14 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
 		return -EPERM;
 
 	/*
+	 * This codepath has no mechanism for verifying that the loaded image
+	 * is trustworthy, so forbid using kexec_load() if the kernel is
+	 * trusted
+	 */
+	if (get_trusted_kernel())
+		return -EPERM;
+
+	/*
 	 * Verify we have a legal set of flags
 	 * This leaves us room for future extensions.
 	 */
@@ -1388,6 +1397,15 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
 	int ret = 0, i;
 	struct kimage **dest_image, *image;
 
+#ifndef CONFIG_KEXEC_VERIFY_SIG
+	/*
+	 * Don't permit images to be loaded into trusted kernels if we're not
+	 * going to verify the signature on them
+	 */
+	if (get_trusted_kernel())
+		return -EPERM;
+#endif
+
 	/* We only trust the superuser with rebooting the system. */
 	if (!capable(CAP_SYS_BOOT) || kexec_load_disabled)
 		return -EPERM;
-- 
2.1.0

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