Re: [Xen-users] Reading a DomU's memory from Dom0 or Xen hypervisor

[Brett Stahlman <brettstahlman@xxxxxxxxx>]

On Mon, Oct 9, 2017 at 4:35 AM, Roger Pau Monné <roger.pau@xxxxxxxxxx> wrote:
> On Fri, Oct 06, 2017 at 04:01:29PM +0000, Brett Stahlman wrote:
>> On Fri, Oct 6, 2017 at 3:51 AM, Roger Pau Monné <roger.pau@xxxxxxxxxx> wrote:
>> > On Thu, Oct 05, 2017 at 05:51:39PM +0000, Brett Stahlman wrote:
>> >> I'd like to be able to read specific memory locations within a DomU,
>> >> either by guest-physical or guest-virtual address, and I'm wondering
>> >> what the Xen-provided options in this area are. I've seen
>> >> documentation on "grant tables", but that mechanism seems tailored
>> >> towards communication between front and back-end drivers. All I want
>> >> to do is allow code in either Dom0 or the hypervisor itself to read
>> >> specific memory ranges within a specific DomU. I notice there's a
>> >> raw_copy_from_guest() function (guestcopy.c), which looks like it
>> >> could be useful. However, the hardcoding of "current->domain" in the
>> >> call to get_page_from_gva() leads me to suspect that it's intended for
>> >> use only in a hypercall. Is there a standard way to read memory from
>> >> an *arbitrary* guest, either using guest-physical or guest-virtual
>> >> addresses? If so, is it possible to do it from Dom0 without modifying
>> >> the Xen hypervisor?
>> >>
>> >> Links to relevant documentation or example source code would be
>> >> greatly appreciated...
>> >
>> > AFAICT you want to take a look at the foreignmemory library. It allows
>> > you to map DomU memory from Dom0 user-space [0].
>>
>> Hmm... Just noticed that the foreignmemory mapping code was factored
>> out of libxc and into libxenforeignmemory in commit 324869 (Xen 4.7).
>> So it looks like there was no alternative to the libxc functions until
>> fairly recently. I'll probably try using the libxenforeignmemory
>> functions (tools/libs/foreignmemory) directly, unless someone can give
>> me a reason to prefer the libxc wrapper...
>
> libxc doesn't have a stable interface, libxenforeignmemory OTOH is
> stable, so you should aim at using the later, or else you
> implementation might be tied to a specific Xen version.

Understood. Thanks.
Brett S.

>
> Roger.

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