[PATCH] cirrus: handle wraparound in cirrus_invalidate_region

[Gerd Hoffmann <kraxel@redhat.com>]

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: Alexander Bulekov <alxndr@bu.edu>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 hw/display/cirrus_vga.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/hw/display/cirrus_vga.c b/hw/display/cirrus_vga.c
index 212d6f5e6145..b91b64347473 100644
--- a/hw/display/cirrus_vga.c
+++ b/hw/display/cirrus_vga.c
@@ -640,10 +640,15 @@ 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 - off_cur);
+            memory_region_set_dirty(&s->vga.vram, 0, off_cur_end);
+        }
         off_begin += off_pitch;
     }
 }
-- 
2.27.0