[PATCH 14/24] x86: Restrict MSR access when the kernel is locked down

[David Howells]

From: Matthew Garrett <matthew.garr...@nebula.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 <keesc...@chromium.org>
Signed-off-by: Matthew Garrett <matthew.garr...@nebula.com>
Signed-off-by: David Howells <dhowe...@redhat.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 ef688804f80d..fbcce028e502 100644
--- a/arch/x86/kernel/msr.c
+++ b/arch/x86/kernel/msr.c
@@ -84,6 +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 */
 
@@ -131,6 +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;