Re: [Xen-devel] [PATCH 1/4] x86/vmx: Don't leak host syscall MSR state into HVM guests

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Andrew Cooper [mailto:amc96@xxxxxxxxxxxxxxxx] On Behalf Of Andrew Cooper
> Sent: Tuesday, February 14, 2017 4:19 PM
> 
> On 14/02/2017 08:04, Tian, Kevin wrote:
> >> From: Andrew Cooper [mailto:amc96@xxxxxxxxxxxxxxxx] On Behalf Of Andrew
> Cooper
> >> Sent: Tuesday, February 14, 2017 3:59 PM
> >>
> >> On 14/02/2017 02:52, Tian, Kevin wrote:
> >>>> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx]
> >>>> Sent: Monday, February 13, 2017 10:32 PM
> >>>>
> >>>> hvm_hw_cpu->msr_flags is in fact the VMX dirty bitmap of MSRs needing to 
> >>>> be
> >>>> restored when switching into guest context.  It should never have been 
> >>>> part of
> >>>> the migration state to start with, and Xen must not make any decisions 
> >>>> based
> >>>> on the value seen during restore.
> >>>>
> >>>> Identify it as obsolete in the header files, consistently save it as 
> >>>> zero and
> >>>> ignore it on restore.
> >>>>
> >>>> The MSRs must be considered dirty during VMCS creation to cause the 
> >>>> proper
> >>>> defaults of 0 to be visible to the guest.
> >>>>
> >>>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> >>> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>, with one small comment.
> >>>
> >>> the effect of this patch should be more than not leaking syscall MSR.
> >>> what about making the subject clearer when check-in?
> >> What other effects do you think are going on here?  Yes, we now context
> >> switch the MSRs right from the start of the domain, but that is
> >> necessary to avoid leaking them.
> >>
> > If just looking at this patch, it's for general MSR save/restore policy,
> > nothing specific to syscall MSR.
> 
> The only three MSRs which use this infrastructure are LSTAR, STAR and
> FMASK.  What if I were to clarify that in the first paragraph?
> 
> ~Andrew

I meant the subject line (talk about syscall MSR leakage) mismatches the 
commit message (for general MSR load)

Thanks
Kevin

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