Function ati_2d_blt() in hw/display/ati-2d.c is affected by an integer overflow
vulnerability leading to potential out-of-bounds read/write operations. 

Specifically, variables `s->regs.dst_x` and `s->regs.dst_y` are set to less than
0x3fff in function ati_mm_write() in ati.c. However, it turns out they can
infinitely increase the size to exceed 0x3fff in the switch case ROP3_SRCCOPY
in function ati_2d_blt(): 

1) when looping, first set `dst_stride` to 0 to pass the check 
   `dst_bits + dst_x + (dst_y + s-> regs.dst_height) * dst_stride> = end`

2) after `dst_x` and `dst_y` assume a large value, `dst_stride` can be set

3) expression `dst_x + (dst_y + s-> regs.dst_height) * dst_stride` can be set
   to a large value (like 0xffffffff). When using a 32-bit operating system,
   the pointer plus 0xffffffff can pass the check.

This will cause wrong memory access leading to out-of-bounds read/write in
function pixman_blt().

Upstream fix:
https://git.qemu.org/?p=qemu.git;a=commit;h=ac2071c3791b67fc7af78b8ceb320c01ca1b5df7