vga: add sr_vbe register set

Commit "fd3c136 vga: make sure vga register setup for vbe stays intact
(CVE-2016-3712)." causes a regression.  The win7 installer is unhappy
because it can't freely modify vga registers any more while in vbe mode.

This patch introduces a new sr_vbe register set.  The vbe_update_vgaregs
will fill sr_vbe[] instead of sr[].  Normal vga register reads and
writes go to sr[].  Any sr register read access happens through a new
sr() helper function which will read from sr_vbe[] with vbe active and
from sr[] otherwise.

This way we can allow guests update sr[] registers as they want, without
allowing them disrupt vbe video modes that way.

Cc: qemu-stable@nongnu.org
Reported-by: Thomas Lamprecht <thomas@lamprecht.org>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 1463475294-14119-1-git-send-email-kraxel@redhat.com

1 files changed, 1 insertions, 0 deletions

diff --git a/hw/display/vga_int.h b/hw/display/vga_int.h
index bdb43a5a34..3ce5544efd 100644
--- a/hw/display/vga_int.h
+++ b/hw/display/vga_int.h
@@ -98,6 +98,7 @@ typedef struct VGACommonState {
     MemoryRegion chain4_alias;
     uint8_t sr_index;
     uint8_t sr[256];
+    uint8_t sr_vbe[256];
     uint8_t gr_index;
     uint8_t gr[256];
     uint8_t ar_index;