Re: EFER in HVM guests

["Jan Beulich" <jbeulich@novell.com>]

>>> Keir Fraser <keir@xensource.com> 29.11.06 14:09 >>>
>On 29/11/06 13:07, "Jan Beulich" <jbeulich@novell.com> wrote:
>
>> Is it intentional that
>> - under SVM, 32-bit guests can freely set EFER.LME
>> - under VMX, 32-bit guests can't access EFER at all?
>> 
>> Thanks, Jan
>
>I'm sure any differences are unintentional. There is obviously scope for
>making much of the MSR and CPUID code non-vmx/svm specific.
>
>I assume that this particular difference doesn't really matter?

I think it does - allowing a guest to enable EFER.LME when the
hypervisor is a 32-bit one is clearly a security problem: While I
haven't tried it, I would suspect the moment you load a context
with such an EFER the whole system's dead.
Not being able to access EFER is also a potential problem, as a
guest should be allowed to set EFER.NX (at least) - the CPUID
handling code specifically does not suppress this bit if the guest
is allowed to use PAE (which we agreed a few days ago should
be the default anyway).

Jan