cirrus: handle wraparound in cirrus_invalidate_region

Code simply asserts that there is no wraparound instead of handling
it properly.  The assert() can be triggered by the guest (must be
privilidged inside the guest though).  Fix it.

Buglink: https://bugs.launchpad.net/qemu/+bug/1880189
Cc: Li Qiang <liq3ea@163.com>
Reported-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Li Qiang <liq3ea@163.com>
Message-id: 20200901140944.24101-1-kraxel@redhat.com

diff --git a/hw/display/cirrus_vga.c b/hw/display/cirrus_vga.c
index 02d9ed0bd46500eca7e5d07fdc9842f61c448251..41e71af08a0f78006b6defa5a348548f495582cf 100644 (file)
--- a/hw/display/cirrus_vga.c
+++ b/hw/display/cirrus_vga.c
@@ -640,10 +640,16 @@ static void cirrus_invalidate_region(CirrusVGAState * s, int off_begin,
     }
 
     for (y = 0; y < lines; y++) {
-        off_cur = off_begin;
+        off_cur = off_begin & s->cirrus_addr_mask;
         off_cur_end = ((off_cur + bytesperline - 1) & s->cirrus_addr_mask) + 1;
-        assert(off_cur_end >= off_cur);
-        memory_region_set_dirty(&s->vga.vram, off_cur, off_cur_end - off_cur);
+        if (off_cur_end >= off_cur) {
+            memory_region_set_dirty(&s->vga.vram, off_cur, off_cur_end - off_cur);
+        } else {
+            /* wraparound */
+            memory_region_set_dirty(&s->vga.vram, off_cur,
+                                    s->cirrus_addr_mask + 1 - off_cur);
+            memory_region_set_dirty(&s->vga.vram, 0, off_cur_end);
+        }
         off_begin += off_pitch;
     }
 }