SAFES: Sand-boxed Architecture for Frequent Environment Self-measurement

Monitoring software of low-end devices is a key part of defense in depth for IoT systems. These devices are particularly susceptible to memory corruption vulnerabilities because the limited computational resources restrict the types of countermeasures that can be implemented. Run-time monitoring therefore is fundamental for the security of these devices. We propose a monitoring architecture for untrusted software at the I/O event granularity for TrustZone-enabled devices. The architecture enables us to measure the integrity of the code immediately before its execution is triggered by any input. To verify the integrity in a lightweight manner, we statically determine the minimal code region that needs to be measured based on the I/O operation. We develop a prototype of the architecture using TrustZone-M and demonstrate that our prototype has a low processing overhead and small ROM memory footprint.