[Qemu-devel] [PATCH] do boundary check based on absolute value

[Glauber Costa]

For backward operations, dstpitch and srcpitch can
be negative. This leads BLTUNSAFE macro into an
overflow, and as a result, it avoids performing
operations that are perfectly valid.

The visible effect that led to that patch was the gnome-panel
bar in Fedora10. Before this patch, you could see garbage
clobbering a big portion of the bar.

After this patch, this garbage is gone.

Signed-off-by: Glauber Costa <address@hidden>
---
 hw/cirrus_vga.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/hw/cirrus_vga.c b/hw/cirrus_vga.c
index e0cf458..5690719 100644
--- a/hw/cirrus_vga.c
+++ b/hw/cirrus_vga.c
@@ -221,15 +221,17 @@
 #define CIRRUS_HOOK_NOT_HANDLED 0
 #define CIRRUS_HOOK_HANDLED 1
 
+#define ABS(a) ((signed)(a) > 0 ? a : -a)
+
 #define BLTUNSAFE(s) \
     ( \
         ( /* check dst is within bounds */ \
-            (s)->cirrus_blt_height * (s)->cirrus_blt_dstpitch \
+            (s)->cirrus_blt_height * ABS((s)->cirrus_blt_dstpitch) \
                 + ((s)->cirrus_blt_dstaddr & (s)->cirrus_addr_mask) > \
                     (s)->vram_size \
         ) || \
         ( /* check src is within bounds */ \
-            (s)->cirrus_blt_height * (s)->cirrus_blt_srcpitch \
+            (s)->cirrus_blt_height * ABS((s)->cirrus_blt_srcpitch) \
                 + ((s)->cirrus_blt_srcaddr & (s)->cirrus_addr_mask) > \
                     (s)->vram_size \
         ) \
-- 
1.5.6.5