REMAP: A Fine-Grained Runtime Memory Protection System for RTOS

Embedded systems rely on real-time operating systems (RTOS) for safety-critical applications, but the absence of fine-grained memory protection poses serious security risks. Existing protection mechanisms either require specialized hardware or rely on static configurations that fail to adapt to dynamic task behavior. This paper introduces Runtime Enforcement of Memory Access Protection (REMAP), which is a novel framework that combines LLVM-based static analysis with runtime Memory Protection Unit (MPU) reconfiguration to achieve fine-grained, dynamic compartmentalization for RTOS environments. REMAP constructs task-specific Access Control Table (ACT) at compile time and enforces them at runtime through on-demand MPU updates triggered by memory access violations. This lazy mapping strategy allows REMAP to support hundreds of compartments per task despite the limitation on the number of hardware MPU slots. Our prototype on ARMv8-M (Cortex-M33) demonstrates that REMAP enforces memory access control down to the function and variable level, protects shared buffers for secure Inter Process Communication (IPC), and prevents error propagation across tasks. Evaluation using the BEEBS benchmark suite shows that compartment merging significantly reduces fault frequency, yielding overheads under 5% across all benchmarks. Therefore, REMAP achieves precise, adaptive memory protection suitable for commercial RTOS deployments without compromising real-time performance.