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@chromium.org>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>

diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
index 113e70784854fb55bdc0eb08fe5e38bee4946126..26c2f83fc47056e5a1d47055c1721924887682f0 100644 (file)
--- a/arch/x86/kernel/msr.c
+++ b/arch/x86/kernel/msr.c
@@ -105,6 +105,9 @@ 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 */
 
@@ -152,6 +155,10 @@ 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;