lkml.org 
[lkml]   [2018]   [Jan]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRE: [PATCH] x86: vmx: Allow direct access to MSR_IA32_SPEC_CTRL
From

>>
>> On Sun, 2018-01-28 at 12:40 -0800, Andy Lutomirski wrote:
>> >
>> > Do you mean that the host would intercept the guest WRMSR and do
>> > WRMSR itself?  I would suggest that doing so is inconsistent with the
>> > docs.  As specified, doing WRMSR to write 1 to IBRS does *not*
>> > protect the guest.
>>
>> I believe it does. Guest kernel is protected from any guest userspace
>> predictions learned before IBRS was last set to 1 in *any* mode,
>> including host.
>
> the specification requires you to write a 1 on each transition to higher
> privilege.

Right. Andy's concern was about VMX non-root (i.e. guest) ring 0
attempting to write IBRS but it's trapped and actually happens in the
host.

As long as it *remains* set when the host re-enters the vCPU that should
be fine.


--
dwmw2

\
 
 \ /
  Last update: 2018-01-28 22:48    [W:0.050 / U:0.116 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site