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Message-ID: <147933295221.19316.10760767173988816147.stgit@warthog.procyon.org.uk>
Date: Wed, 16 Nov 2016 21:49:12 +0000
From: David Howells <dhowells@...hat.com>
To: keyrings@...r.kernel.org
Cc: matthew.garrett@...ula.com, linux-efi@...r.kernel.org,
Kees Cook <keescook@...omium.org>,
linux-kernel@...r.kernel.org, dhowells@...hat.com,
linux-security-module@...r.kernel.org
Subject: [PATCH 16/16] x86: Restrict MSR access when the kernel is locked
down
From: Matthew Garrett <matthew.garrett@...ula.com>
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@...omium.org>
Signed-off-by: Matthew Garrett <matthew.garrett@...ula.com>
Signed-off-by: David Howells <dhowells@...hat.com>
---
arch/x86/kernel/msr.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
index 7f3550acde1b..b875e54bdbf7 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(®s, uregs, sizeof regs)) {
err = -EFAULT;
break;
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