[PATCH] ati-vga: increment mm_index in ati_mm_read/write

[P J P <ppandit@redhat.com>]

From: Prasad J Pandit <pjp@fedoraproject.org>

While accessing VGA registers via ati_mm_read/write routines,
a guest may set 's->regs.mm_index' such that it leads to infinite
recursion. Increment the mm_index value to avoid it.

Reported-by: Ren Ding <rding@gatech.edu>
Reported-by: Hanqing Zhao <hanqing@gatech.edu>
Reported-by: Yi Ren <c4tren@gmail.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 hw/display/ati.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/hw/display/ati.c b/hw/display/ati.c
index 065f197678..fa9061ad0b 100644
--- a/hw/display/ati.c
+++ b/hw/display/ati.c
@@ -286,7 +286,8 @@ static uint64_t ati_mm_read(void *opaque, hwaddr addr, unsigned int size)
                 val = ldn_le_p(s->vga.vram_ptr + idx, size);
             }
         } else {
-            val = ati_mm_read(s, s->regs.mm_index + addr - MM_DATA, size);
+            uint32_t idx = s->regs.mm_index++;
+            val = ati_mm_read(s, idx + addr - MM_DATA, size);
         }
         break;
     case BIOS_0_SCRATCH ... BUS_CNTL - 1:
@@ -521,7 +522,8 @@ static void ati_mm_write(void *opaque, hwaddr addr,
                 stn_le_p(s->vga.vram_ptr + idx, size, data);
             }
         } else {
-            ati_mm_write(s, s->regs.mm_index + addr - MM_DATA, data, size);
+            uint32_t idx = s->regs.mm_index++;
+            ati_mm_write(s, idx + addr - MM_DATA, data, size);
         }
         break;
     case BIOS_0_SCRATCH ... BUS_CNTL - 1:
-- 
2.26.2