Re: [Xen-devel] [PATCH] HVM x86_32 PAE guest support on 64-bit Xen

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 19 Feb 2006, at 07:58, Keir Fraser wrote:

> > The VMX does not save/restore NXE (bit 11) and SCE (bit 0), and they 
> > are
> > always set in Xen (on machines where VMX is available). So it's 
> > possible
> > that those bits are still effectively on in the guest even after the
> > guest attempted to clear them (and we ignore such writes). I don't 
> > think
> > bad things can happen practically. We need to check carefully if we
> > might expose security holes there.
> Isn't SYSENTER effectively disabled if SYSENTER_CS == 0? Presumably 
> the guest wouldn't touch that MSR unless it intends to set SCE.
Oops, SCE enables SYSCALL. Yes, that might be a problem -- I think 
there is no 'safety catch' except for that EFER flag. Possibly the MSR 
does need save/restore on context switch.
 -- Keir


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