vbe: make bochs dispi interface return the correct memory size with qxl

VgaState->vram_size is the size of the pci bar.  In case of qxl not the
whole pci bar can be used as vga framebuffer.  Add a new variable
vbe_size to handle that case.  By default (if unset) it equals
vram_size, but qxl can set vbe_size to something else.

This makes sure VBE_DISPI_INDEX_VIDEO_MEMORY_64K returns correct results
and sanity checks are done with the correct size too.

Cc: qemu-stable@nongnu.org
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
vbe: rework sanity checks

Plug a bunch of holes in the bochs dispi interface parameter checking.
Add a function doing verification on all registers.  Call that
unconditionally on every register write.  That way we should catch
everything, even changing one register affecting the valid range of
another register.

Some of the holes have been added by commit
e9c6149f6ae6873f14a12eea554925b6aa4c4dec.  Before that commit the
maximum possible framebuffer (VBE_DISPI_MAX_XRES * VBE_DISPI_MAX_YRES *
32 bpp) has been smaller than the qemu vga memory (8MB) and the checking
for VBE_DISPI_MAX_XRES + VBE_DISPI_MAX_YRES + VBE_DISPI_MAX_BPP was ok.

Some of the holes have been there forever, such as
VBE_DISPI_INDEX_X_OFFSET and VBE_DISPI_INDEX_Y_OFFSET register writes
lacking any verification.

Security impact:

(1) Guest can make the ui (gtk/vnc/...) use memory rages outside the vga
frame buffer as source  ->  host memory leak.  Memory isn't leaked to
the guest but to the vnc client though.

(2) Qemu will segfault in case the memory range happens to include
unmapped areas  ->  Guest can DoS itself.

The guest can not modify host memory, so I don't think this can be used
by the guest to escape.

CVE-2014-3615

Cc: qemu-stable@nongnu.org
Cc: secalert@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
spice: make sure we don't overflow ssd->buf

Related spice-only bug.  We have a fixed 16 MB buffer here, being
presented to the spice-server as qxl video memory in case spice is
used with a non-qxl card.  It's also used with qxl in vga mode.

When using display resolutions requiring more than 16 MB of memory we
are going to overflow that buffer.  In theory the guest can write,
indirectly via spice-server.  The spice-server clears the memory after
setting a new video mode though, triggering a segfault in the overflow
case, so qemu crashes before the guest has a chance to do something
evil.

Fix that by switching to dynamic allocation for the buffer.

CVE-2014-3615

Cc: qemu-stable@nongnu.org
Cc: secalert@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Merge remote-tracking branch 'remotes/kraxel/tags/pull-cve-2014-3615-20140905-1' into staging

CVE-2014-3615: fix sanity checks in vbe (bochs dispi) and spice.

# gpg: Signature made Fri 05 Sep 2014 12:18:04 BST using RSA key ID D3E87138
# gpg: Good signature from "Gerd Hoffmann (work) <kraxel@redhat.com>"
# gpg:                 aka "Gerd Hoffmann <gerd@kraxel.org>"
# gpg:                 aka "Gerd Hoffmann (private) <kraxel@gmail.com>"

* remotes/kraxel/tags/pull-cve-2014-3615-20140905-1:
  spice: make sure we don't overflow ssd->buf
  vbe: rework sanity checks
  vbe: make bochs dispi interface return the correct memory size with qxl

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>