Re: Fw: [Xen-devel] Xen on /. again

[Mark Williamson <Mark.Williamson@xxxxxxxxxxxx>]

> Information about other domains' memory usage is leaked via the
> hardware->physical mapping.

OK, I was forgetting about the domain memory reservation hypercalls.  It's 
probably reasonable just to throw away ballooning functionality where this 
might be a problem.

The main problem (as I see it) is going to be the network interface, whose 
performance depends on page-flipping.  You can eliminate the security problem 
without hiding machine address if you copy incoming packets but that's going 
to hurt performance :-(

> > Timing related attacks are somewhat trickier to eliminate covert channels
> > in, although some randomisation can limit the bandwidth.
>
> Eliminating covert channels is completely infeasible. I don't see any
> value in aiming for this. It's not a useful security property in most
> circumstances.

I agree it's not useful in the majority of circumstances.  If it's required it 
can be implemented at a later date but the returns for the amount of time 
invested are likely to be smaller.

Cheers,
Mark


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