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

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

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.

Tamas

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