Re: [PATCH] x86: Lock down MSR writing in secure boot
[Posted March 12, 2013 by mkerrisk]
| From: |
| Kees Cook <keescook-F7+t8E8rja9g9hUCZPvPmw-AT-public.gmane.org> |
| To: |
| "H. Peter Anvin" <hpa-YMNOUZJC4hwAvxtiuMwx3w-AT-public.gmane.org> |
| Subject: |
| Re: [PATCH] x86: Lock down MSR writing in secure boot |
| Date: |
| Fri, 8 Feb 2013 11:18:54 -0800 |
| Message-ID: |
| <CAGXu5jJnLY6Qp3J6HBpVg-AdUGdKYm-e4wErZO3=NuRo04ajvg@mail.gmail.com> |
| Cc: |
| LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA-AT-public.gmane.org>,
Matthew Garrett <matthew.garrett-05XSO3Yj/JvQT0dZR+AlfA-AT-public.gmane.org>,
Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ-AT-public.gmane.org>,
Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA-AT-public.gmane.org>, x86-DgEjT+Ai2ygdnm+yROfE0A-AT-public.gmane.org,
linux-efi-u79uwXL29TY76Z2rM5mHXA-AT-public.gmane.org,
linux-security-module <linux-security-module-u79uwXL29TY76Z2rM5mHXA-AT-public.gmane.org> |
| Archive‑link: | |
Article |
No. CAP_RAWIO is for reading. Writing needs a much stronger check.
-Kees
On Fri, Feb 8, 2013 at 11:17 AM, H. Peter Anvin <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>
wrote:
> We already have CAP_RAWIO for this in mainline; I am not sure if this should be harder than
that...
>
> Kees Cook <keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.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 <keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.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(®s, uregs, sizeof regs)) {
>> err = -EFAULT;
>> break;
>
> --
> Sent from my mobile phone. Please excuse brevity and lack of formatting.
--
Kees Cook
Chrome OS Security
