spapr_rtas: Prevent QEMU crash during hotplug without a prior device_add

If drmgr is used in the guest to hotplug a device before a device_add
has been issued via the QEMU monitor, QEMU segfaults in configure_connector
call. This occurs due to accessing of NULL FDT which otherwise would have
been created and associated with the DRC during device_add command.

Check for NULL FDT and return failure from configure_connector call.
As per PAPR+, an error value of -9003 seems appropriate for this failure.

Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Cc: Michael Roth <mdroth@linux.vnet.ibm.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

hw/ppc/spapr_rtas.c

@@ -522,6 +522,12 @@ static void rtas_ibm_configure_connector(PowerPCCPU *cpu,
 
     drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
     fdt = drck->get_fdt(drc, NULL);
+    if (!fdt) {
+        DPRINTF("rtas_ibm_configure_connector: Missing FDT for DRC index: %xh\n",
+                drc_index);
+        rc = SPAPR_DR_CC_RESPONSE_NOT_CONFIGURABLE;
+        goto out;
+    }
 
     ccs = spapr_ccs_find(spapr, drc_index);
     if (!ccs) {

include/hw/ppc/spapr_drc.h

@@ -119,13 +119,14 @@ typedef enum {
 } sPAPRDREntitySense;
 
 typedef enum {
-    SPAPR_DR_CC_RESPONSE_NEXT_SIB       = 1, /* currently unused */
-    SPAPR_DR_CC_RESPONSE_NEXT_CHILD     = 2,
-    SPAPR_DR_CC_RESPONSE_NEXT_PROPERTY  = 3,
-    SPAPR_DR_CC_RESPONSE_PREV_PARENT    = 4,
-    SPAPR_DR_CC_RESPONSE_SUCCESS        = 0,
-    SPAPR_DR_CC_RESPONSE_ERROR          = -1,
-    SPAPR_DR_CC_RESPONSE_CONTINUE       = -2,
+    SPAPR_DR_CC_RESPONSE_NEXT_SIB         = 1, /* currently unused */
+    SPAPR_DR_CC_RESPONSE_NEXT_CHILD       = 2,
+    SPAPR_DR_CC_RESPONSE_NEXT_PROPERTY    = 3,
+    SPAPR_DR_CC_RESPONSE_PREV_PARENT      = 4,
+    SPAPR_DR_CC_RESPONSE_SUCCESS          = 0,
+    SPAPR_DR_CC_RESPONSE_ERROR            = -1,
+    SPAPR_DR_CC_RESPONSE_CONTINUE         = -2,
+    SPAPR_DR_CC_RESPONSE_NOT_CONFIGURABLE = -9003,
 } sPAPRDRCCResponse;
 
 typedef void (spapr_drc_detach_cb)(DeviceState *d, void *opaque);