In seL4's virtualization support, VM exceptions are turned into messages and handled by VMM, a task running in unprivileged mode. VMM has no more capabilities

In seL4's virtualization support, VM exceptions are turned into messages and handled by VMM, a task running in unprivileged mode. VMM has no more capabilities than the VM itself, thus a VM escape would be, outside of academics, of no value. Refer to pages 8 to 10 in the OP PDF.