Re: [Qemu-devel] [RFC] host and guest kernel trace merging

[Steven Rostedt <rostedt@goodmis.org>]

On Mon, 7 Mar 2016 09:10:10 -0700
Eric Blake <eblake@redhat.com> wrote:

> On 03/07/2016 08:49 AM, Steven Rostedt wrote:
> > On Mon, 7 Mar 2016 15:17:05 +0000
> > Stefan Hajnoczi <stefanha@redhat.com> wrote:
> > 
> >   
> >> qemu-guest-agent runs inside the guest and replies to RPC commands from
> >> the host.  It is used for backups, shutdown, network configuration, etc.
> >> From time to time people have wanted the ability to execute an arbitrary
> >> command inside the guest and return the output.  This functionality has
> >> never been merged, probably for the security reason.  
> > 
> > How's the connection set up. That is, how does it know the commands are
> > coming from the host? And how does it know that the commands from the
> > host is from a trusted source? If the host is compromised, is there
> > anything keeping an intruder from controlling the guest?  
> 
> qemu-guest-agent uses a virtio channel, so only the host can be driving
> that channel.  But how can a guest know that it trusts the host? It
> can't.  A compromised host implicitly compromises all guests, and that's
> always been the case.  At least qemu-guest-agent doesn't make the window
> any larger.
> 

I should have been a bit more clear about what I meant by "host is
compromised". I should have asked, what about untrusted tasks on the
host. Is the channel protected where only admin users can access it?

Of course, one of my concerns with the trace-cmd server is that it may
require a network connection, because doesn't a virtio channel require
to be initialized at boot up? Where the host must have an active
listener when the guest starts? Or am I thinking about something else.

-- Steve