StackLock with simple FSM

With a wide spread of malicious software attacks, run-time stack has been drawing attention because it is one of the most vulnerable points in computer architecture. Conventional stack layout, in which local variables for user input and control flow data such as return address are saved close to each other, is often the root of the attack vulnerability. This paper proposes a simple finite state machine to track usage of stack frame locations at a fine granularity of 2-bytes. Such a fine grain protection is necessary to distinguish adjacent stack frame locations, which allows detecting abnormal memory operations even in real mode running of a boot loader. The proposed scheme guarantees 2-byte granularity for preventing malicious writes in the stack using small additional memory space for the finite state machine.