A Realization of IO Physical Memory Protection for RISC-V Systems

Physical memories or RAMs are essential components in a computer system to hold temporary information required for both software and hardware to work properly. When a system's security is compromised (e.g., due to a malicious application), sensitive information being held in the memories can be leaked out for example to “the cloud”. The RISC-V privileged architecture standard adopts a method called Physical Memory Protection (PMP) to segregate a system's memory into regions with different policy and permissions to prevent unprivileged software from accessing unauthorized regions. However, PMP does not prevent malicious software from hijacking an Input/Output (IO) device with Direct Memory Access (DMA) capability to indirectly gain unauthorized accesses and hence, a similar method commonly termed as “IOPMP” is being worked on in the RISC-V community. This paper describes an early implementation of IOPMP and how it is used to protect physical memory regions in a RISC-V system. Then, the potential performance impact of IOPMP is briefly elaborated. There are still work to be done and this early IOPMP implementation allows various aspects of the protection method such as its scalability, practicality, and effectiveness etc. to be studied for future enhancement.