hw/intc/xics: Add a check for an invalid server id

A malformed IVE value can result in an invalid server field being
passed to icp_irq(). The function assumes the server id is valid and
may access invalid state otherwise, potentially leading to a crash.

Fix this by validating the server id before using it and ignoring
invalid values.

Reported-by: Zexiang Zhang <chan9yan9@gmail.com>
Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3324
Signed-off-by: Zexiang Zhang <chan9yan9@gmail.com>
Signed-off-by: Gautam Menghani <gautam@linux.ibm.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Link: https://lore.kernel.org/qemu-devel/20260428103645.50617-1-Gautam.Menghani@ibm.com
Signed-off-by: Harsh Prateek Bora <harshpb@linux.ibm.com>

hw/intc/xics.c

@@ -26,6 +26,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/log.h"
 #include "qapi/error.h"
 #include "trace.h"
 #include "qemu/timer.h"
@@ -222,6 +223,13 @@ void icp_irq(ICSState *ics, int server, int nr, uint8_t priority)
 
     trace_xics_icp_irq(server, nr, priority);
 
+    if (!icp) {
+        qemu_log_mask(LOG_GUEST_ERROR, "XICS: invalid server %d for IRQ 0x%x\n",
+                      server, nr);
+        ics_reject(ics, nr);
+        return;
+    }
+
     if ((priority >= CPPR(icp))
         || (XISR(icp) && (icp->pending_priority <= priority))) {
         ics_reject(ics, nr);