vga display update mis-calculated the region for the dirty bitmap snapshot in case split screen mode is used. This can trigger an assert in cpu_physical_memory_snapshot_get_dirty().
Impact: DoS for privileged guest users. Fixes: CVE-2017-13673 Fixes: fec5e8c92becad223df9d972770522f64aafdb72 Cc: P J P <ppan...@redhat.com> Reported-by: David Buchanan <d...@vidbuchanan.co.uk> Signed-off-by: Gerd Hoffmann <kra...@redhat.com> --- hw/display/vga.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/hw/display/vga.c b/hw/display/vga.c index 63421f9ee8..ab33668402 100644 --- a/hw/display/vga.c +++ b/hw/display/vga.c @@ -1628,9 +1628,15 @@ static void vga_draw_graphic(VGACommonState *s, int full_update) y1 = 0; if (!full_update) { + ram_addr_t region_start = addr1; + ram_addr_t region_end = addr1 + line_offset * height; vga_sync_dirty_bitmap(s); - snap = memory_region_snapshot_and_clear_dirty(&s->vram, addr1, - line_offset * height, + if (s->line_compare < height) { + /* split screen mode */ + region_start = 0; + } + snap = memory_region_snapshot_and_clear_dirty(&s->vram, region_start, + region_end - region_start, DIRTY_MEMORY_VGA); } -- 2.9.3