Re: [PATCH] x86: Lock down MSR writing in secure boot

[H. Peter Anvin]

We already have CAP_RAWIO for this in mainline; I am not sure if this should be 
harder than that...

Kees Cook <keesc...@chromium.org> wrote:

>Writing to MSRs should not be allowed unless CAP_COMPROMISE_KERNEL is
>set since it could lead to execution of arbitrary code in kernel mode.
>
>Signed-off-by: Kees Cook <keesc...@chromium.org>
>---
>This would be used on top of Matthew Garrett's existing "Secure boot
>policy support" patch series.
>---
> 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 4929502..adaab3d 100644
>--- a/arch/x86/kernel/msr.c
>+++ b/arch/x86/kernel/msr.c
>@@ -103,6 +103,9 @@ static ssize_t msr_write(struct file *file, const
>char __user *buf,
>       int err = 0;
>       ssize_t bytes = 0;
> 
>+      if (!capable(CAP_COMPROMISE_KERNEL))
>+              return -EPERM;
>+
>       if (count % 8)
>               return -EINVAL; /* Invalid chunk size */
> 
>@@ -150,6 +153,10 @@ static long msr_ioctl(struct file *file, unsigned
>int ioc, unsigned long arg)
>                       err = -EBADF;
>                       break;
>               }
>+              if (!capable(CAP_COMPROMISE_KERNEL)) {
>+                      err = -EPERM;
>+                      break;
>+              }
>               if (copy_from_user(&regs, uregs, sizeof regs)) {
>                       err = -EFAULT;
>                       break;

-- 
Sent from my mobile phone. Please excuse brevity and lack of formatting.
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