1. A system for preventing unauthorized modification of an operating system, comprising: a processing unit; a system memory in communication with said processing unit; an operating system for controlling the operation of said processing unit, said operating system comprised of kernel code; and an enforcement agent executing at a higher privilege than said kernel code, wherein the enforcement agent prevents unauthorized modification of existing kernel code and injection of new code with kernel privilege by maintaining shadow copies of a global descriptor table, a local descriptor table, and one or more registers, and by only permitting entry pointers contained within the global descriptor table, the local descriptor table, and the one or more registers to point to approved kernel code.