[PATCH 09/20] x86: Restrict MSR access when module loading is restricted

[Josh Boyer]

From: Matthew Garrett <matthew.garr...@nebula.com>

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 <keesc...@chromium.org>
Signed-off-by: Matthew Garrett <matthew.garr...@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 7f3550acde1b..963ba4011923 100644
--- a/arch/x86/kernel/msr.c
+++ b/arch/x86/kernel/msr.c
@@ -83,6 +83,9 @@ 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 */
 
@@ -130,6 +133,10 @@ 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;
-- 
2.9.3
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