Re: [Xen-research] Intercepting memory operations of a guest

["Todd Deshane" <deshantm@xxxxxxxxx>]

On Sun, Dec 7, 2008 at 8:57 PM, Sina Bahram <sbahram@xxxxxxxxx> wrote:
> Hi all,
>
> Sorry for any cross posting. I sent this to the xen-devel list and the
> xen-se list as well.
>
> I'm wanting to modify some xen source code for the purposes of some
> research, exploration, and testing of some security concepts.
>
> I have a few questions after looking through the source.
>
> All of the below applies to 32-bit guests.
>
> #1: Is there anyway possible to trap/insert some code at/hook into, any
> modification of a PV guest's page table. Anything like a hypercall handler I
> can plugin to, a function or series of functions that always gets called,
> something I can provide a call back to, or anything else?
>
> #2: For some research purposes, I plan on replicating portions of the page
> table of a guest, only those pages of the guest's kernel. I hope to do this
> by the supervisory bit being set; however, I welcome any suggestions of a
> better approach to detecting when kernel pages are being modified?
>
> In general, to explain any questions I haven't specifically asked above; I'm
> looking for the appropriate place in xen to intercept any writes, reads, and
> executes of a guest's memory.
>
> Also, would such activities be easier or more difficult with hvm guests?
> Since xen has to provide hvm guests an individual CR3, would such a place be
> much easier to hook into because of any abstraction layers that already
> exist for such things?
>
> The only reason I picked pv guests was that the semantics of what is a
> kernel page and what is not might not be as easy to determine in an hvm
> guest, but perhaps this is not the case?
>

You may want to take a look at the Xen Introspection Project:
http://blog.xen.org/index.php/2008/10/27/new-xen-introspection-project-launching/
http://blog.xen.org/index.php/2008/11/12/xen-introspect-project-update/

Cheers,
Todd

-- 
Todd Deshane
http://todddeshane.net
http://runningxen.com

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