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

[David Hopwood <david.nospam.hopwood@xxxxxxxxxxxxxxxx>]

Mark Williamson wrote:
> > Also, I suppose you will wish to prevent covert channels between
> > domains, e.g. domains communicating using various timing attacks (I move
> > the disk head to the other end of the disk if I wish to tell you
> > something), or by allocating/freeing certains parts of memory.
> >
> > How much will you need to dumb down the VMs view of what is going on in
> > the machine to achieve this (not expose real time information, not
> > expose real page tables), and how much of a VMM will there be left when
> > you are done?
> Well domains are not aware of each other's memory usage, so I wouldn't have 
> thought that allocation / exposing real page tables would matter.  (Except 
> dom0 can of course see everything if it wants).
Information about other domains' memory usage is leaked via the
hardware->physical mapping.

> 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.

--
David Hopwood <david.nospam.hopwood@xxxxxxxxxxxxxxxx>



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