This challenge has a similar hierarchy as "Abyss" has, which is also my series of challenges in HITCON CTF 2018. Abyss contains three layers as well, the user-space program, the kernel, and the hypervisor, but with the self-implemented kernel and hypervisor based on KVM.
For PoE, I modified the latest QEMU source code to add a custom device, Treap Processing Unit (TPU), developed a Linux kernel module to drive my fancy device, and a simple note editor in user-space that utilize TPU to perform string operations.
I have released all the source code and my exploit scripts for this challenge, along with the patch needed for Linux kernel and QEMU.