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

[Brett Stahlman <brettstahlman@xxxxxxxxx>]

Excellent. The function xenforeignmemory_map() looks like it may do
what I want. There's also function xc_map_foreign_range(), defined
in... libs/libxc/xc_foreign_memory.c. Is libxc meant to be used only
from tools like xc/xl? I notice that it delegates the actual mapping
to xenforeignmemory_map(). Are you aware of any benefits provided by
the extra level of indirection?

Thanks,
Brett S.

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].
>
> Roger.
>
> [0] 
> http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=tools/libs/foreignmemory/core.c

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