[PATCH v7 2/7] xen/events: don't allow binding a global virq from any domain

[Juergen Gross <jgross@suse.com>]

Today Xen will happily allow binding a global virq by a domain which
isn't configured to receive it. This won't result in any bad actions,
but the bind will appear to have succeeded with no event ever being
received by that event channel.

Instead of allowing the bind, error out if the domain isn't set to
handle that virq. Note that this check is inside the write_lock() on
purpose, as a future patch will put a related check into
set_global_virq_handler() with the addition of using the same lock.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
V6:
- new patch
V7:
- move handling domain check inside locked region (Jan Beulich)
- style fix (Jan Beulich)
---
 xen/common/event_channel.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/xen/common/event_channel.c b/xen/common/event_channel.c
index 46281b16ce..cd6f5a1211 100644
--- a/xen/common/event_channel.c
+++ b/xen/common/event_channel.c
@@ -120,6 +120,13 @@ static uint8_t get_xen_consumer(xen_event_channel_notification_t fn)
 /* Get the notification function for a given Xen-bound event channel. */
 #define xen_notification_fn(e) (xen_consumers[(e)->xen_consumer-1])
 
+static struct domain *__read_mostly global_virq_handlers[NR_VIRQS];
+
+static struct domain *get_global_virq_handler(unsigned int virq)
+{
+    return global_virq_handlers[virq] ?: hardware_domain;
+}
+
 static bool virq_is_global(unsigned int virq)
 {
     switch ( virq )
@@ -469,6 +476,7 @@ int evtchn_bind_virq(evtchn_bind_virq_t *bind, evtchn_port_t port)
     struct domain *d = current->domain;
     int            virq = bind->virq, vcpu = bind->vcpu;
     int            rc = 0;
+    bool           is_global;
 
     if ( (virq < 0) || (virq >= ARRAY_SIZE(v->virq_to_evtchn)) )
         return -EINVAL;
@@ -478,8 +486,9 @@ int evtchn_bind_virq(evtchn_bind_virq_t *bind, evtchn_port_t port)
     * speculative execution.
     */
     virq = array_index_nospec(virq, ARRAY_SIZE(v->virq_to_evtchn));
+    is_global = virq_is_global(virq);
 
-    if ( virq_is_global(virq) && (vcpu != 0) )
+    if ( is_global && vcpu != 0 )
         return -EINVAL;
 
     if ( (v = domain_vcpu(d, vcpu)) == NULL )
@@ -487,6 +496,12 @@ int evtchn_bind_virq(evtchn_bind_virq_t *bind, evtchn_port_t port)
 
     write_lock(&d->event_lock);
 
+    if ( is_global && get_global_virq_handler(virq) != d )
+    {
+        rc = -EBUSY;
+        goto out;
+    }
+
     if ( read_atomic(&v->virq_to_evtchn[virq]) )
     {
         rc = -EEXIST;
@@ -965,15 +980,13 @@ void send_guest_pirq(struct domain *d, const struct pirq *pirq)
     }
 }
 
-static struct domain *global_virq_handlers[NR_VIRQS] __read_mostly;
-
 static DEFINE_SPINLOCK(global_virq_handlers_lock);
 
 void send_global_virq(uint32_t virq)
 {
     ASSERT(virq_is_global(virq));
 
-    send_guest_global_virq(global_virq_handlers[virq] ?: hardware_domain, virq);
+    send_guest_global_virq(get_global_virq_handler(virq), virq);
 }
 
 int set_global_virq_handler(struct domain *d, uint32_t virq)
-- 
2.43.0