Protection Mechanism in Privileged Memory Space for Embedded Systems, Real-Time OS

Memory protection mechanisms have become important in embedded systems because programs are becoming larger and more complex, and the failure of one program can corrupt other programs. In order to isolate failures and to prevent the failure of one program from propagating throughout the system, memory protection is required. Recently, memory protection is also required in safety-critical embedded systems. In embedded systems, the memory protection mechanisms are used the memory management unit (MMU) function in a CPU. However, the overhead cost of system calls to the OS is very large because the system calls are implemented by a software trap, which decreases the system performance. The goal of the present study is to provide a lightweight memory protection mechanism in the privilege memory space in order to protect a real-time OS from unintended behaviors of application programs in the privilege memory space. An application program in the privilege level in an embedded system, which is accessible to registers in peripheral devices and can execute privilege instructions for the embedded system, is crucial. We design and implement the light memory protection mechanism in the privilege memory space in real-time OS using MMU in ARM processor. We show that our memory protection mechanism is effective in a real application because of very small increase of execution time.