From: Matthew Garrett <matthew.garrett@nebula.com>
Date: Mon, 9 Sep 2013 22:49:44 +0000 (-0700)
Subject: x86: Restrict MSR access when securelevel is set
X-Git-Tag: v4.1.12-92~310^2~5
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=5c700e60c8c54a4f552af3bd79b5c4e431b761f1;p=users%2Fjedix%2Flinux-maple.git

x86: Restrict MSR access when securelevel is set

Orabug: 21539498

Permitting write access to MSRs allows userspace to modify the running
kernel. Prevent this if securelevel has been set. 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: Santosh Shilimkar <santosh.shilimkar@oracle.com>
---

diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
index 113e70784854..979517195ec0 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/processor.h>
 #include <asm/msr.h>
@@ -105,6 +106,9 @@ static ssize_t msr_write(struct file *file, const char __user *buf,
 	int err = 0;
 	ssize_t bytes = 0;
 
+	if (get_securelevel() > 0)
+		return -EPERM;
+
 	if (count % 8)
 		return -EINVAL;	/* Invalid chunk size */
 
@@ -152,6 +156,10 @@ static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
 			err = -EBADF;
 			break;
 		}
+		if (get_securelevel() > 0) {
+			err = -EPERM;
+			break;
+		}
 		if (copy_from_user(&regs, uregs, sizeof regs)) {
 			err = -EFAULT;
 			break;