experiments with isolation on blue pill
Summary
The article documents an embedded systems experiment: building a semi-hypervisor/ supervisor for a Cortex-M3 (Blue Pill) without TrustZone or MMU, using the MPU to create isolated regions. It describes architecture with a privileged bootloader-supervisor and an unprivileged application module, each with separate flash and RAM, and a runtime patch mechanism. It explains privilege transitions via SVC and CONTROL, how the supervisor monitors app health with a watchdog, and discusses limitations such as DMA bypasses and potential vulnerability gaps.