[PATCH 05/12] evtchn/sched: reject poll requests for unusable ports

[Jan Beulich <jbeulich@xxxxxxxx>]

Before and after XSA-342 there has been an asymmetry in how not really
usable ports get treated in do_poll(): Ones beyond a certain boundary
(max_evtchns originally, valid_evtchns subsequently) did get refused
with -EINVAL, while lower ones were accepted despite there potentially
being no way to wake the vCPU again from its polling state. Arrange to
also honor evtchn_usable() output in the decision.

Requested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/common/sched/core.c
+++ b/xen/common/sched/core.c
@@ -1427,13 +1427,13 @@ static long do_poll(struct sched_poll *s
         if ( __copy_from_guest_offset(&port, sched_poll->ports, i, 1) )
             goto out;
 
-        rc = -EINVAL;
-        if ( !port_is_valid(d, port) )
-            goto out;
-
-        rc = 0;
-        if ( evtchn_port_is_pending(d, port) )
+        rc = evtchn_port_poll(d, port);
+        if ( rc )
+        {
+            if ( rc > 0 )
+                rc = 0;
             goto out;
+        }
     }
 
     if ( sched_poll->nr_ports == 1 )
--- a/xen/include/xen/event.h
+++ b/xen/include/xen/event.h
@@ -240,19 +240,6 @@ static inline bool evtchn_is_pending(con
     return evtchn_usable(evtchn) && d->evtchn_port_ops->is_pending(d, evtchn);
 }
 
-static inline bool evtchn_port_is_pending(struct domain *d, evtchn_port_t port)
-{
-    struct evtchn *evtchn = evtchn_from_port(d, port);
-    bool rc;
-    unsigned long flags;
-
-    spin_lock_irqsave(&evtchn->lock, flags);
-    rc = evtchn_is_pending(d, evtchn);
-    spin_unlock_irqrestore(&evtchn->lock, flags);
-
-    return rc;
-}
-
 static inline bool evtchn_is_masked(const struct domain *d,
                                     const struct evtchn *evtchn)
 {
@@ -279,6 +266,24 @@ static inline bool evtchn_is_busy(const
            d->evtchn_port_ops->is_busy(d, evtchn);
 }
 
+static inline int evtchn_port_poll(struct domain *d, evtchn_port_t port)
+{
+    int rc = -EINVAL;
+
+    if ( port_is_valid(d, port) )
+    {
+        struct evtchn *evtchn = evtchn_from_port(d, port);
+        unsigned long flags;
+
+        spin_lock_irqsave(&evtchn->lock, flags);
+        if ( evtchn_usable(evtchn) )
+            rc = evtchn_is_pending(d, evtchn);
+        spin_unlock_irqrestore(&evtchn->lock, flags);
+    }
+
+    return rc;
+}
+
 static inline int evtchn_port_set_priority(struct domain *d,
                                            struct evtchn *evtchn,
                                            unsigned int priority)