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[Xen-research] Intercepting memory operations of a guest

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Subject: [Xen-research] Intercepting memory operations of a guest
From: "Sina Bahram" <sbahram@xxxxxxxxx>
Date: Sun, 7 Dec 2008 20:57:30 -0500
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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?

Thanks for any assistance.

Take care,

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