Re: [Xen-devel] Blocking CR and MSR writes via mem_access?

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.10.14 at 12:49, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> Currently hvm_memory_event_cr3() and the other hvm_memory_event_*()
> functions in hvm.c can pause the VCPU and send a mem_event with the new
> value of the respective register, but especially in the case of CR
> events (as opposed to MSR events), this is done _after_ the value is set
> (please see hvm_set_cr3() in hvm.c).
> 
> It would be interesting from a memory introspection application's point
> of view to be able to receive a mem_event _before_ the value is set, and
> important to be able to veto the change.

So what do you expect the effect of denying the write to be?
Wouldn't crashing the guest explicitly have about the same effect?

> 1. Would it be acceptable to move the CR3 event sending code so that a
> mem_access client would receive the event _before_ the write takes
> place? Is this likely to break other mem_event clients that might rely
> on the event being received _after_ the value has been set?

I don't think you should break existing behavior. If you need an
event before the setting gets carried out, just add another one.

Jan


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