[Xen-devel] [PATCH 09/32] cirrus_vga: fix division by 0 for color expansion rop

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

From: Aurelien Jarno <aurelien@xxxxxxxxxxx>

Commit d85d0d3883f5a567fa2969a0396e42e0a662b3fa introduces a regression
with Windows ME that leads to a division by 0 and a crash.

It uses the color expansion rop with the source pitch set to 0. This is
something allowed, as the manual explicitely says "When the source of
color-expand data is display memory, the source pitch is ignored.".

This patch fixes this regression by computing sx, sy and others
variables only if they are going to be used later, that is for a plain
copy ROP. It basically consists in moving code.

Signed-off-by: Aurelien Jarno <aurelien@xxxxxxxxxxx>
---
 hw/cirrus_vga.c |   70 +++++++++++++++++++++++++++----------------------------
 1 file changed, 35 insertions(+), 35 deletions(-)

diff --git a/hw/cirrus_vga.c b/hw/cirrus_vga.c
index d3bf4cf..e6c3893 100644
--- a/hw/cirrus_vga.c
+++ b/hw/cirrus_vga.c
@@ -754,46 +754,46 @@ static int 
cirrus_bitblt_videotovideo_patterncopy(CirrusVGAState * s)
 
 static void cirrus_do_copy(CirrusVGAState *s, int dst, int src, int w, int h)
 {
-    int sx, sy;
-    int dx, dy;
-    int width, height;
-    int depth;
+    int sx = 0, sy = 0;
+    int dx = 0, dy = 0;
+    int depth = 0;
     int notify = 0;
 
-    depth = s->get_bpp((VGAState *)s) / 8;
-    s->get_resolution((VGAState *)s, &width, &height);
-
-    /* extra x, y */
-    sx = (src % ABS(s->cirrus_blt_srcpitch)) / depth;
-    sy = (src / ABS(s->cirrus_blt_srcpitch));
-    dx = (dst % ABS(s->cirrus_blt_dstpitch)) / depth;
-    dy = (dst / ABS(s->cirrus_blt_dstpitch));
-
-    /* normalize width */
-    w /= depth;
-
-    /* if we're doing a backward copy, we have to adjust
-       our x/y to be the upper left corner (instead of the lower
-       right corner) */
-    if (s->cirrus_blt_dstpitch < 0) {
-       sx -= (s->cirrus_blt_width / depth) - 1;
-       dx -= (s->cirrus_blt_width / depth) - 1;
-       sy -= s->cirrus_blt_height - 1;
-       dy -= s->cirrus_blt_height - 1;
-    }
+    /* make sure to only copy if it's a plain copy ROP */
+    if (*s->cirrus_rop == cirrus_bitblt_rop_fwd_src ||
+        *s->cirrus_rop == cirrus_bitblt_rop_bkwd_src) {
+        int width, height;
+
+        depth = s->get_bpp((VGAState *)s) / 8;
+        s->get_resolution((VGAState *)s, &width, &height);
+
+        /* extra x, y */
+        sx = (src % ABS(s->cirrus_blt_srcpitch)) / depth;
+        sy = (src / ABS(s->cirrus_blt_srcpitch));
+        dx = (dst % ABS(s->cirrus_blt_dstpitch)) / depth;
+        dy = (dst / ABS(s->cirrus_blt_dstpitch));
+
+        /* normalize width */
+        w /= depth;
+
+        /* if we're doing a backward copy, we have to adjust
+           our x/y to be the upper left corner (instead of the lower
+           right corner) */
+        if (s->cirrus_blt_dstpitch < 0) {
+            sx -= (s->cirrus_blt_width / depth) - 1;
+            dx -= (s->cirrus_blt_width / depth) - 1;
+            sy -= s->cirrus_blt_height - 1;
+            dy -= s->cirrus_blt_height - 1;
+        }
 
-    /* are we in the visible portion of memory? */
-    if (sx >= 0 && sy >= 0 && dx >= 0 && dy >= 0 &&
-       (sx + w) <= width && (sy + h) <= height &&
-       (dx + w) <= width && (dy + h) <= height) {
-       notify = 1;
+        /* are we in the visible portion of memory? */
+        if (sx >= 0 && sy >= 0 && dx >= 0 && dy >= 0 &&
+            (sx + w) <= width && (sy + h) <= height &&
+            (dx + w) <= width && (dy + h) <= height) {
+            notify = 1;
+        }
     }
 
-    /* make to sure only copy if it's a plain copy ROP */
-    if (*s->cirrus_rop != cirrus_bitblt_rop_fwd_src &&
-       *s->cirrus_rop != cirrus_bitblt_rop_bkwd_src)
-       notify = 0;
-
     /* we have to flush all pending changes so that the copy
        is generated at the appropriate moment in time */
     if (notify)
-- 
1.7.10.4


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