diff mbox series

[PULL,03/10] hw/xen: prevent guest from binding loopback event channel to itself

Message ID 20230801215421.60133-4-philmd@linaro.org
State Accepted
Commit 75a87af9b228ca7d14902a9390fe5e83c4898eb0
Headers show
Series [PULL,01/10] hw/xen: fix off-by-one in xen_evtchn_set_gsi() | expand

Commit Message

Philippe Mathieu-Daudé Aug. 1, 2023, 9:54 p.m. UTC 
From: David Woodhouse <dwmw@amazon.co.uk>

Fuzzing showed that a guest could bind an interdomain port to itself, by
guessing the next port to be allocated and putting that as the 'remote'
port number. By chance, that works because the newly-allocated port has
type EVTCHNSTAT_unbound. It shouldn't.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
Message-Id: <20230801175747.145906-4-dwmw2@infradead.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 hw/i386/kvm/xen_evtchn.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/hw/i386/kvm/xen_evtchn.c b/hw/i386/kvm/xen_evtchn.c
index 0e9c108614..a731738411 100644
--- a/hw/i386/kvm/xen_evtchn.c
+++ b/hw/i386/kvm/xen_evtchn.c
@@ -1408,8 +1408,15 @@  int xen_evtchn_bind_interdomain_op(struct evtchn_bind_interdomain *interdomain)
         XenEvtchnPort *rp = &s->port_table[interdomain->remote_port];
         XenEvtchnPort *lp = &s->port_table[interdomain->local_port];
 
-        if (rp->type == EVTCHNSTAT_unbound && rp->type_val == 0) {
-            /* It's a match! */
+        /*
+         * The 'remote' port for loopback must be an unbound port allocated for
+         * communication with the local domain (as indicated by rp->type_val
+         * being zero, not PORT_INFO_TYPEVAL_REMOTE_QEMU), and must *not* be
+         * the port that was just allocated for the local end.
+         */
+        if (interdomain->local_port != interdomain->remote_port &&
+            rp->type == EVTCHNSTAT_unbound && rp->type_val == 0) {
+
             rp->type = EVTCHNSTAT_interdomain;
             rp->type_val = interdomain->local_port;