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vga: fix display update region calculation (split screen) 

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: fec5e8c92b
Cc: P J P <ppandit@redhat.com>
Reported-by: David Buchanan <d@vidbuchanan.co.uk>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 20170828123307.15392-1-kraxel@redhat.com
This commit is contained in:
Gerd Hoffmann 2017-08-28 14:33:07 +02:00
parent 223cd0e13f
commit e65294157d
1 changed files with 8 additions and 2 deletions
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10
hw/display/vga.c
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@ -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);
}