[Qemu-devel] [PULL 1/1] qdev: Fix assert in PCI address property when used by vfio-pci

[Eduardo Habkost <ehabkost@redhat.com>]

From: Daniel Oram <daniel.oram@gmail.com>

Allow the PCIHostDeviceAddress structure to work as the host property
in vfio-pci when it has it's default value of all fields set to ~0. In
this form the property indicates a non-existant device but given the
field bit sizes gets asserted as excess (and invalid) precision
overflows the string buffer. The BDF of an invalid device
"FFFF:FF:FF.F" is returned instead.

Signed-off-by: Daniel Oram <daniel.oram@gmail.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Message-Id: <71f06765c4ba16dcd71cbf78e877619948f04ed9.1478777270.git.daniel.oram@gmail.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 hw/core/qdev-properties.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/hw/core/qdev-properties.c b/hw/core/qdev-properties.c
index 311af6d..2a82768 100644
--- a/hw/core/qdev-properties.c
+++ b/hw/core/qdev-properties.c
@@ -705,13 +705,19 @@ static void get_pci_host_devaddr(Object *obj, Visitor *v, const char *name,
     DeviceState *dev = DEVICE(obj);
     Property *prop = opaque;
     PCIHostDeviceAddress *addr = qdev_get_prop_ptr(dev, prop);
-    char buffer[] = "xxxx:xx:xx.x";
+    char buffer[] = "ffff:ff:ff.f";
     char *p = buffer;
     int rc = 0;
 
-    rc = snprintf(buffer, sizeof(buffer), "%04x:%02x:%02x.%d",
-                  addr->domain, addr->bus, addr->slot, addr->function);
-    assert(rc == sizeof(buffer) - 1);
+    /*
+     * Catch "invalid" device reference from vfio-pci and allow the
+     * default buffer representing the non-existant device to be used.
+     */
+    if (~addr->domain || ~addr->bus || ~addr->slot || ~addr->function) {
+        rc = snprintf(buffer, sizeof(buffer), "%04x:%02x:%02x.%0d",
+                      addr->domain, addr->bus, addr->slot, addr->function);
+        assert(rc == sizeof(buffer) - 1);
+    }
 
     visit_type_str(v, name, &p, errp);
 }
-- 
2.7.4