Re: [Xen-devel] protecting xen startup

[Mark Williamson <maw48@xxxxxxxxxxxxxxxx>]

> are you hinting at the allocation of device drivers across domains?
>
> e.g. having one domain do the hardware side and securely
> proxy-forwarding the access to that device over to another domain?
Well, this is really already done.  e.g. net and block devices are 
securely shared.  Domain 0 runs the real physical device driver and the 
unprivileged domain uses a virtual device driver to communicate its 
requests to dom0.  These are requests are validated before being accepted.
Setting up these "device channels" is reasonably involved.  A protocol 
using the control message framework is used to communicate to the 
"backend" (runs in dom0 and co-ordinates sharing) and "frontend" (runs in 
guest and provides virtual devices to the guest) about what virtual 
devices exist.  The protocol is then used to establish a shared-memory 
connection between the two.
One problem here is that domain 0's control interface (used to communicate 
with the backend drivers) can only have one writer.  Hence it's necessary 
to ensure mutual exclusion - we let Xend control writing requests to this 
interface.
As well as keeping track of various forms of state, you also need to 
ensure that the control interface is dealt with correctly, which could be 
quite a bit of work.
> ... but i have to point out that i'm more concerned about leveraging
> what is available - right now - than i am about future versions.
Sure thing.  We're planning to add mandatory access control features at 
some stage but that's still on the drawing board at the moment.  In the 
meantime, there should be plenty of other fun to be had...
Cheers,
Mark


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