[Qemu-devel] [PATCH] cirrus: fix oob access issue

[Li Qiang <liq3ea@gmail.com>]

From: Li Qiang <liqiang6-s@360.cn>

When doing bitblt copy in backward mode, we should minus the
blt width first just like the adding in the forward mode. This
can avoid the oob access of the front of vga's vram.

Signed-off-by: Li Qiang <liqiang6-s@360.cn>
---
 hw/display/cirrus_vga.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/display/cirrus_vga.c b/hw/display/cirrus_vga.c
index 379910d..fa56730 100644
--- a/hw/display/cirrus_vga.c
+++ b/hw/display/cirrus_vga.c
@@ -277,7 +277,8 @@ static bool blit_region_is_unsafe(struct CirrusVGAState *s,
     }
     if (pitch < 0) {
         int64_t min = addr
-            + ((int64_t)s->cirrus_blt_height-1) * pitch;
+            + ((int64_t)s->cirrus_blt_height - 1) * pitch
+            - s->cirrus_blt_width;
         int32_t max = addr
             + s->cirrus_blt_width;
         if (min < 0 || max > s->vga.vram_size) {
-- 
1.8.3.1