Re: [Qemu-devel] [PATCH v2 3/3] Add rate limiting of RTC_CHANGE, BALLOON_CHANGE & WATCHDOG events

[Luiz Capitulino <lcapitulino@redhat.com>]

On Fri, 8 Jun 2012 17:48:56 +0100
"Daniel P. Berrange" <berrange@redhat.com> wrote:

> On Wed, May 30, 2012 at 03:50:37PM -0300, Luiz Capitulino wrote:
> > On Mon, 21 May 2012 17:59:53 +0100
> > "Daniel P. Berrange" <berrange@redhat.com> wrote:
> 
> > > +/* Global, one-time initializer to configure the rate limiting
> > > + * and initialize state */
> > > +static void monitor_protocol_event_init(void)
> > > +{
> > > +    qemu_mutex_init(&monitor_event_state_lock);
> > > +    /* Limit RTC & BALLOON events to 1 per second */
> > > +    monitor_protocol_event_throttle(QEVENT_RTC_CHANGE, 1000);
> > > +    monitor_protocol_event_throttle(QEVENT_BALLOON_CHANGE, 1000);
> > > +    monitor_protocol_event_throttle(QEVENT_WATCHDOG, 1000);
> > 
> > What about SUSPENDED and BLOCK_IO_ERROR? Couldn't the former be also
> > used by a malicious guest to cause a DoS? The former is already emitted
> > several times for virtio.
> 
> This can't be used to filter BLOCK_IO_ERROR, since that event
> contains per-device state information. Filtering this would
> need to be done in the block layer, so it can done per device.

That's right.

> I don't think SUSPEND can be used to DoS, since once the VM
> is in the suspend state, a monitor command is required to wake
> it up again before the guest OS can trigger a new suspend.

Can't the guest OS awake itself?