From: Juergen Gross jgross@suse.com
commit fe415186b43df0db1f17fa3a46275fd92107fe71 upstream.
The Xen console driver is still vulnerable for an attack via excessive number of events sent by the backend. Fix that by using a lateeoi event channel.
For the normal domU initial console this requires the introduction of bind_evtchn_to_irq_lateeoi() as there is no xenbus device available at the time the event channel is bound to the irq.
As the decision whether an interrupt was spurious or not requires to test for bytes having been read from the backend, move sending the event into the if statement, as sending an event without having found any bytes to be read is making no sense at all.
This is part of XSA-391
Signed-off-by: Juergen Gross jgross@suse.com Reviewed-by: Jan Beulich jbeulich@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/tty/hvc/hvc_xen.c | 30 +++++++++++++++++++++++++++--- 1 file changed, 27 insertions(+), 3 deletions(-)
--- a/drivers/tty/hvc/hvc_xen.c +++ b/drivers/tty/hvc/hvc_xen.c @@ -50,6 +50,8 @@ struct xencons_info { struct xenbus_device *xbdev; struct xencons_interface *intf; unsigned int evtchn; + XENCONS_RING_IDX out_cons; + unsigned int out_cons_same; struct hvc_struct *hvc; int irq; int vtermno; @@ -151,6 +153,8 @@ static int domU_read_console(uint32_t vt XENCONS_RING_IDX cons, prod; int recv = 0; struct xencons_info *xencons = vtermno_to_xencons(vtermno); + unsigned int eoiflag = 0; + if (xencons == NULL) return -EINVAL; intf = xencons->intf; @@ -170,7 +174,27 @@ static int domU_read_console(uint32_t vt mb(); /* read ring before consuming */ intf->in_cons = cons;
- notify_daemon(xencons); + /* + * When to mark interrupt having been spurious: + * - there was no new data to be read, and + * - the backend did not consume some output bytes, and + * - the previous round with no read data didn't see consumed bytes + * (we might have a race with an interrupt being in flight while + * updating xencons->out_cons, so account for that by allowing one + * round without any visible reason) + */ + if (intf->out_cons != xencons->out_cons) { + xencons->out_cons = intf->out_cons; + xencons->out_cons_same = 0; + } + if (recv) { + notify_daemon(xencons); + } else if (xencons->out_cons_same++ > 1) { + eoiflag = XEN_EOI_FLAG_SPURIOUS; + } + + xen_irq_lateeoi(xencons->irq, eoiflag); + return recv; }
@@ -399,7 +423,7 @@ static int xencons_connect_backend(struc if (ret) return ret; info->evtchn = evtchn; - irq = bind_evtchn_to_irq(evtchn); + irq = bind_interdomain_evtchn_to_irq_lateeoi(dev->otherend_id, evtchn); if (irq < 0) return irq; info->irq = irq; @@ -563,7 +587,7 @@ static int __init xen_hvc_init(void) return r;
info = vtermno_to_xencons(HVC_COOKIE); - info->irq = bind_evtchn_to_irq(info->evtchn); + info->irq = bind_evtchn_to_irq_lateeoi(info->evtchn); } if (info->irq < 0) info->irq = 0; /* NO_IRQ */