kvmvapic: Catch invalid ROM size

If not caught early, a zero-length ROM will cause a NULL-pointer access
later on in patch_hypercalls when allocating a zero-length ROM copy and
trying to read from it.

CC: qemu-stable@nongnu.org
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 9 insertions, 2 deletions

diff --git a/hw/i386/kvmvapic.c b/hw/i386/kvmvapic.c
index d3a6fbe1f9..c66fbf2fdb 100644
--- a/hw/i386/kvmvapic.c
+++ b/hw/i386/kvmvapic.c
@@ -578,7 +578,7 @@ static int patch_hypercalls(VAPICROMState *s)
  * enable write access to the option ROM so that variables can be updated by
  * the guest.
  */
-static void vapic_map_rom_writable(VAPICROMState *s)
+static int vapic_map_rom_writable(VAPICROMState *s)
 {
     hwaddr rom_paddr = s->rom_state_paddr & ROM_BLOCK_MASK;
     MemoryRegionSection section;
@@ -599,6 +599,9 @@ static void vapic_map_rom_writable(VAPICROMState *s)
     /* read ROM size from RAM region */
     ram = memory_region_get_ram_ptr(section.mr);
     rom_size = ram[rom_paddr + 2] * ROM_BLOCK_SIZE;
+    if (rom_size == 0) {
+        return -1;
+    }
     s->rom_size = rom_size;
 
     /* We need to round to avoid creating subpages
@@ -612,11 +615,15 @@ static void vapic_map_rom_writable(VAPICROMState *s)
     memory_region_add_subregion_overlap(as, rom_paddr, &s->rom, 1000);
     s->rom_mapped_writable = true;
     memory_region_unref(section.mr);
+
+    return 0;
 }
 
 static int vapic_prepare(VAPICROMState *s)
 {
-    vapic_map_rom_writable(s);
+    if (vapic_map_rom_writable(s) < 0) {
+        return -1;
+    }
 
     if (patch_hypercalls(s) < 0) {
         return -1;