Umbra: An Efficient Framework for Trusted Execution on Modern TrustZone-Enabled Microcontrollers

The rise of microcontrollers in critical systems demands robust security measures beyond traditional methods like Memory Protection Units. ARM's TrustZone-M offers enhanced protection for secure applications, yet its potential for deploying Trusted Execution Environments often remains untapped, leaving room for innovation in managing security on resource-constrained devices. This paper presents Umbra, a Rust-based framework that isolates mutually distrustful applications and integrates with untrusted embedded OSes. Leveraging modern security hardware, Umbra features an efficient secure caching mechanism that encrypts all code exposed to attackers, decrypting and validating only necessary blocks during execution, achieving practical Trusted Execution Environments on modern microcontrollers.