x86: Restrict MSR access when the kernel is locked down Writing to MSRs should not be allowed if the kernel is locked down, since it could lead to execution of arbitrary code in kernel mode. Based on a patch by Kees Cook. Cc: Kees Cook <keescook@chromium.org> Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com> Signed-off-by: David Howells <dhowells@redhat.com>

diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
index 7f3550a..b875e54 100644
--- a/arch/x86/kernel/msr.c
+++ b/arch/x86/kernel/msr.c

@@ -39,6 +39,7 @@
 #include <linux/notifier.h>
 #include <linux/uaccess.h>
 #include <linux/gfp.h>
+#include <linux/security.h>
 
 #include <asm/cpufeature.h>
 #include <asm/msr.h>
@@ -83,6 +84,9 @@ static ssize_t msr_write(struct file *file, const char __user *buf,
 	int err = 0;
 	ssize_t bytes = 0;
 
+	if (kernel_is_locked_down())
+		return -EPERM;
+
 	if (count % 8)
 		return -EINVAL;	/* Invalid chunk size */
 
@@ -130,6 +134,10 @@ static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
 			err = -EBADF;
 			break;
 		}
+		if (kernel_is_locked_down()) {
+			err = -EPERM;
+			break;
+		}
 		if (copy_from_user(&regs, uregs, sizeof regs)) {
 			err = -EFAULT;
 			break;