hw/intc/arm_gicv3_its: Range-check ICID before indexing into collection table

In process_its_cmd(), we read an ICID out of the interrupt table
entry, and then use it as an index into the collection table.  Add a
check that it is within range for the collection table first.

This check is not strictly necessary, because:
 * we range check the ICID from the guest before writing it into
   the interrupt table entry, so the the only way to get an
   out of range ICID in process_its_cmd() is if a badly-behaved
   guest is writing directly to the interrupt table memory
 * the collection table is in guest memory, so QEMU won't fall
   over if we read off the end of it

However, it seems clearer to include the check.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20220111171048.3545974-14-peter.maydell@linaro.org

hw/intc/arm_gicv3_its.c

@@ -299,6 +299,13 @@ static ItsCmdResult process_its_cmd(GICv3ITSState *s, uint64_t value,
         return CMD_CONTINUE;
     }
 
+    if (icid >= s->ct.num_ids) {
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "%s: invalid ICID 0x%x in ITE (table corrupted?)\n",
+                      __func__, icid);
+        return CMD_CONTINUE;
+    }
+
     cte_valid = get_cte(s, icid, &cte, &res);
     if (res != MEMTX_OK) {
         return CMD_STALL;