On (Sun) 06 Jul 2014 [23:09:49], Kees Cook wrote: > On Sun, Jul 6, 2014 at 10:51 PM, Amit Shah <amit.shah@xxxxxxxxxx> wrote: > > On (Sun) 06 Jul 2014 [21:38:36], Kees Cook wrote: > >> On Fri, Jul 4, 2014 at 10:34 PM, Amit Shah <amit.shah@xxxxxxxxxx> wrote: > >> > The hwrng core asks for random data in the hwrng_register() call itself > >> > from commit d9e7972619. This doesn't play well with virtio -- the > >> > DRIVER_OK bit is only set by virtio core on a successful probe, and > >> > we're not yet out of our probe routine when this call is made. This > >> > causes the host to not acknowledge any requests we put in the virtqueue, > >> > and the insmod or kernel boot process just waits for data to arrive from > >> > the host, which never happens. > >> > >> Doesn't this mean that virtio-rng won't ever contribute entropy to the system? > > > > The initial randomness? Yes. But it'll start contributing entropy as > > soon as it's used as the current source. > > How does that happen? I don't see an init function defined for it? I mean the regular usage; not the initial randomness patch that you added. Initial randomness from virtio-rng currently won't be sourced. That's no different from the way things were before your patch; and I can't think of a way to make that happen for now. virtio's probe() has to finish before communication with the host can start. If a virtio-rng device is the only hwrng in the system (very likely in a guest), it's almost guaranteed that hwrng_init() won't be called after hwrng_register() completes (as it would have already been called and the virtio-rng device will have become the current_rng). If the VM admin configured two virtio-rng sources, though, or hotplugged one later, the early randomness will be obtained for the second virtio-rng device. But this is a scenario I don't expect to ever arise -- it's just a theoretical possibility. Amit _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
