hw/ppc/spapr: Fix crash when specifying bad parameters to spapr-pci-host-bridge

QEMU currently crashes when using bad parameters for the
spapr-pci-host-bridge device:

$ qemu-system-ppc64 -device spapr-pci-host-bridge,buid=0x123,liobn=0x321,mem_win_addr=0x1,io_win_addr=0x10
Segmentation fault

The problem is that spapr_tce_find_by_liobn() might return NULL, but
the code in spapr_populate_pci_dt() does not check for this condition
and then tries to dereference this NULL pointer.
Apart from that, the return value of spapr_populate_pci_dt() also
has to be checked for all PCI buses, not only for the last one, to
make sure we catch all errors.
Signed-off-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NDavid Gibson <david@gibson.dropbear.id.au>

hw/ppc/spapr.c

@@ -940,11 +940,10 @@ static void spapr_finalize_fdt(sPAPRMachineState *spapr,
 
     QLIST_FOREACH(phb, &spapr->phbs, list) {
         ret = spapr_populate_pci_dt(phb, PHANDLE_XICP, fdt);
-    }
-
-    if (ret < 0) {
-        fprintf(stderr, "couldn't setup PCI devices in fdt\n");
-        exit(1);
+        if (ret < 0) {
+            error_report("couldn't setup PCI devices in fdt");
+            exit(1);
+        }
     }
 
     /* RTAS */

hw/ppc/spapr_pci.c

@@ -1816,6 +1816,9 @@ int spapr_populate_pci_dt(sPAPRPHBState *phb,
                      sizeof(interrupt_map)));
 
     tcet = spapr_tce_find_by_liobn(SPAPR_PCI_LIOBN(phb->index, 0));
+    if (!tcet) {
+        return -1;
+    }
     spapr_dma_dt(fdt, bus_off, "ibm,dma-window",
                  tcet->liobn, tcet->bus_offset,
                  tcet->nb_table << tcet->page_shift);