Kernel software installed and running inside a Guest VM may post improper commands to the GPU...

Kernel software installed and running inside a Guest VM may post improper commands to the GPU Firmware to trigger a read and/or write data outside the Guest's virtualised GPU memory.

The firmware uses data provided by the Guest VM to set up accesses to memory. It validated this before use, but a TOCTOU bug was present which allowed the earlier check results to be invalidated.