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SubjectRe: [PATCH 12/27] x86/msr: Restrict MSR access when the kernel is locked down
On Thu, Oct 19, 2017 at 03:52:04PM +0100, David Howells wrote:
> From: Matthew Garrett <matthew.garrett@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.
>
> Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>
> Signed-off-by: David Howells <dhowells@redhat.com>
> Acked-by: Kees Cook <keescook@chromium.org>
> Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

I have reviewed this patch. Please feel free to add:

Reviewed-by: "Lee, Chun-Yi" <jlee@suse.com>

Thanks!
Joey Lee

> cc: x86@kernel.org
> ---
>
> 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..a05a97863286 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("Direct MSR access"))
> + 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("Direct MSR access")) {
> + err = -EPERM;
> + break;
> + }
> if (copy_from_user(&regs, uregs, sizeof regs)) {
> err = -EFAULT;
> break;
>
> --
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