Re: [Xen-devel] [PATCH v2] x86/hvm: Allow guest_request vm_events coming from userspace

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 01.08.2017 19:07, Tamas K Lengyel wrote:
> On Tue, Aug 1, 2017 at 4:30 AM, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> > On 01/08/17 10:46, Alexandru Isaila wrote:
> > > Allow guest userspace code to request that a vm_event be sent out
> > > via VMCALL. This functionality seems to be handy for a number of
> > > Xen developers, as stated on the mailing list (thread "[Xen-devel]
> > > HVMOP_guest_request_vm_event only works from guest in ring0").
> > > This is a use case in communication between a userspace application
> > > in the guest and the introspection application in dom0.
> > >
> > > Signed-off-by: Alexandru Isaila <aisaila@xxxxxxxxxxxxxxx>
> > This issue has been argued several times before, and while I am in
> > favour of the change, there is a legitimate argument that it breaks one
> > of our security boundaries.
> >
> > One intermediate option comes to mind however.
> >
> > Could we introduce a new monitor op which permits the use of
> > HVMOP_guest_request_vm_event from userspace?  This way, it requires a
> > positive action on behalf of the introspection agent to relax the CPL
> > check, rather than having the CPL check unconditionally relaxed.
> I agree, it would be required to gate this on a monitor option that is
> disabled by default.
That's the way we'll move forward. About that: would you prefer a new 
libxc function that toggles only the userspace part, or that we add a 
bool parameter to the existing xc_monitor_guest_request()?

Thanks,
Razvan

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