hw/display/qxl: Avoid buffer overrun in qxl_phys2virt (CVE-2022-4144)

hw/display/qxl: Avoid buffer overrun in qxl_phys2virt (CVE-2022-4144)

Have qxl_get_check_slot_offset() return false if the requested
buffer size does not fit within the slot memory region.

Similarly qxl_phys2virt() now returns NULL in such case, and
qxl_dirty_one_surface() aborts.

This avoids buffer overrun in the host pointer returned by
memory_region_get_ram_ptr().

Fixes: CVE-2022-4144 (out-of-bounds read)
Reported-by: Wenxu Yin (@awxylitol)
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1336
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20221128202741.4945-5-philmd@linaro.org>