This implements smooth scrolling, as used for example by Commander Keen
and Second Reality.
Unfortunately, this is not enough to avoid tearing in Commander Keen,
because sometimes the wrong start address is used for a frame.
On real EGA, the panning register is sampled on every line, while
the display start is latched for the next frame at the start of the
vertical retrace. On real VGA, the panning register is also latched,
but at the end of the vertical retrace. It looks like Keen exploits
this by only waiting for horizontal retrace when setting the display
start, but implementing it breaks the 256-color Keen games...
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This allows setting the start address to a high value, and reading the
bottom of the screen from the beginning of VRAM. Commander Keen 4
("Goodbye, Galaxy!") relies on this behavior.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Instead pass around the address (aka offset into vga memory).
Add vga_read_* helper functions which apply vbe_size_mask to
the address, to make sure the address stays within the valid
range, similar to the cirrus blitter fixes (commits ffaf857778
and 026aeffcb4).
Impact: DoS for privileged guest users. qemu crashes with
a segfault, when hitting the guard page after vga memory
allocation, while reading vga memory for display updates.
Fixes: CVE-2017-13672
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: 20170828122906.18993-1-kraxel@redhat.com
It's no longer a template, we only instanciate the file once.
Keep it a #included file so the functions remain static.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
