lkml.org 
[lkml]   [2013]   [Feb]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH] x86: Lock down MSR writing in secure boot
From
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@zytor.com> wrote:
> We already have CAP_RAWIO for this in mainline; I am not sure if this should be harder than that...
>
> Kees Cook <keescook@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 <keescook@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.



--
Kees Cook
Chrome OS Security


\
 
 \ /
  Last update: 2013-02-08 21:01    [W:0.063 / U:26.920 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site