[Qemu-devel] [PATCH] monitor: Fix crashes when using HMP commands without CPU

[Thomas Huth]

When running certain HMP commands ("info registers", "info cpustats"
or dumping virtual memory) with the "none" machine, QEMU crashes
with a segmentation fault. This happens because the "none" machine does
not have any CPUs by default, but these HMP commands did not check for
a valid CPU pointer yet. Add such a check now and print a message
about the missing CPU instead.

Signed-off-by: Thomas Huth <th...@redhat.com>
---
 monitor.c | 29 +++++++++++++++++++++++++----
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/monitor.c b/monitor.c
index 0841d43..0103979 100644
--- a/monitor.c
+++ b/monitor.c
@@ -1025,6 +1025,9 @@ int monitor_set_cpu(int cpu_index)
 CPUState *mon_get_cpu(void)
 {
     if (!cur_mon->mon_cpu) {
+        if (!first_cpu) {
+            return NULL;
+        }
         monitor_set_cpu(first_cpu->cpu_index);
     }
     cpu_synchronize_state(cur_mon->mon_cpu);
@@ -1043,7 +1046,13 @@ int monitor_get_cpu_index(void)
 
 static void hmp_info_registers(Monitor *mon, const QDict *qdict)
 {
-    cpu_dump_state(mon_get_cpu(), (FILE *)mon, monitor_fprintf, CPU_DUMP_FPU);
+    CPUState *cs = mon_get_cpu();
+
+    if (!cs) {
+        monitor_printf(mon, "No CPU available\n");
+        return;
+    }
+    cpu_dump_state(cs, (FILE *)mon, monitor_fprintf, CPU_DUMP_FPU);
 }
 
 static void hmp_info_jit(Monitor *mon, const QDict *qdict)
@@ -1076,7 +1085,13 @@ static void hmp_info_history(Monitor *mon, const QDict 
*qdict)
 
 static void hmp_info_cpustats(Monitor *mon, const QDict *qdict)
 {
-    cpu_dump_statistics(mon_get_cpu(), (FILE *)mon, &monitor_fprintf, 0);
+    CPUState *cs = mon_get_cpu();
+
+    if (!cs) {
+        monitor_printf(mon, "No CPU available\n");
+        return;
+    }
+    cpu_dump_statistics(cs, (FILE *)mon, &monitor_fprintf, 0);
 }
 
 static void hmp_info_trace_events(Monitor *mon, const QDict *qdict)
@@ -1235,6 +1250,12 @@ static void memory_dump(Monitor *mon, int count, int 
format, int wsize,
     int l, line_size, i, max_digits, len;
     uint8_t buf[16];
     uint64_t v;
+    CPUState *cs = mon_get_cpu();
+
+    if (!cs && (format == 'i' || !is_physical)) {
+        monitor_printf(mon, "Can not dump without CPU\n");
+        return;
+    }
 
     if (format == 'i') {
         int flags = 0;
@@ -1264,7 +1285,7 @@ static void memory_dump(Monitor *mon, int count, int 
format, int wsize,
         flags = msr_le << 16;
         flags |= env->bfd_mach;
 #endif
-        monitor_disas(mon, mon_get_cpu(), addr, count, is_physical, flags);
+        monitor_disas(mon, cs, addr, count, is_physical, flags);
         return;
     }
 
@@ -1303,7 +1324,7 @@ static void memory_dump(Monitor *mon, int count, int 
format, int wsize,
         if (is_physical) {
             cpu_physical_memory_read(addr, buf, l);
         } else {
-            if (cpu_memory_rw_debug(mon_get_cpu(), addr, buf, l, 0) < 0) {
+            if (cpu_memory_rw_debug(cs, addr, buf, l, 0) < 0) {
                 monitor_printf(mon, " Cannot access memory\n");
                 break;
             }
-- 
1.8.3.1