From: Matthew Garrett Date: Wed, 5 Apr 2017 17:40:30 +0100 Subject: [51/61] x86: Restrict MSR access when the kernel is locked down Origin: https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/commit?id=e20ab2be2f77e6c0da7cd8fe0953a367c5012ecf 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 Signed-off-by: Matthew Garrett Signed-off-by: David Howells --- 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(®s, uregs, sizeof regs)) { err = -EFAULT; break;