[PATCH secure-modules 08/13] x86: Restrict MSR access when module loading is restricted

[Josh Boyer]

>From 012ac79f54ab746114d8276d8858a3df18b10e22 Mon Sep 17 00:00:00 2001
From: Matthew Garrett <matthew.garrett at nebula.com>
Date: Mon, 19 Aug 2013 13:26:10 -0400
Subject: [PATCH 08/13] x86: Restrict MSR access when module loading is
 restricted

Writing to MSRs should not be allowed if module loading is restricted,
since it could lead to execution of arbitrary code in kernel mode. Based
on a patch by Kees Cook.

Cc: Kees Cook <keescook at chromium.org>
Signed-off-by: Matthew Garrett <matthew.garrett at nebula.com>
---
 arch/x86/kernel/msr.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
index 88458fa..d08f7e3 100644
--- a/arch/x86/kernel/msr.c
+++ b/arch/x86/kernel/msr.c
@@ -103,6 +103,9 @@ static ssize_t msr_write(struct file *file, const char __user *buf,
 	int err = 0;
 	ssize_t bytes = 0;
 
+	if (secure_modules())
+		return -EPERM;
+
 	if (count % 8)
 		return -EINVAL;	/* Invalid chunk size */
 
@@ -150,6 +153,10 @@ static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
 			err = -EBADF;
 			break;
 		}
+		if (secure_modules()) {
+			err = -EPERM;
+			break;
+		}
 		if (copy_from_user(&regs, uregs, sizeof regs)) {
 			err = -EFAULT;
 			break;
-- 
1.8.3.1