Re: Fw: Xen on /. again

[David Hopwood <david.nospam.hopwood@blueyonder.co.uk>]

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@blueyonder.co.uk>



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