Virtualbox is an out-of-tree module and hence needs to be compiled. The base package is GPLv2 and is compatible with the Linux kernel license, but I don't know if Virtualbox developers ever tried to "upstream" their module. This is probably the easiest way to solve your problem. Most Virtualization Software these days use virtualization hardware extensions (Intel VMX/AMD SVM) and so the "hypervisor code" needs to be able to execute privileged instructions, eg - you can't run VMON from ring 3/userspace.