multiboot: Limit number of multiboot modules

Add size checks to avoid overwriting the multiboot structure
when too many modules are loaded.

Patchworks-ID: 35700
Signed-off-by: NAdam Lackorzynski <adam@os.inf.tu-dresden.de>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/pc.c

@@ -702,6 +702,10 @@ static int load_multiboot(void *fw_cfg,
         int mb_mod_count = 0;
 
         do {
+            if (mb_mod_info + 16 > mb_mod_cmdline) {
+                printf("WARNING: Too many modules loaded, aborting.\n");
+                break;
+            }
             next_initrd = strchr(initrd_filename, ',');
             if (next_initrd)
                 *next_initrd = '\0';
@@ -712,8 +716,11 @@ static int load_multiboot(void *fw_cfg,
                     initrd_filename);
             stl_p(bootinfo + mb_mod_info + 8, mb_bootinfo + mb_mod_cmdline); /* string */
             mb_mod_cmdline += strlen(initrd_filename) + 1;
-            if (mb_mod_cmdline > sizeof(bootinfo))
+            if (mb_mod_cmdline > sizeof(bootinfo)) {
                 mb_mod_cmdline = sizeof(bootinfo);
+                printf("WARNING: Too many module cmdlines loaded, aborting.\n");
+                break;
+            }
             if ((next_space = strchr(initrd_filename, ' ')))
                 *next_space = '\0';
 #ifdef DEBUG_MULTIBOOT