User-level Enclave Protection Scheme based on ARM TrustZone

All Existing popular commercial trusted execution environment (TEE) technologies include ARM TrustZone and Intel SGX, which are widely deployed to secure sensitive digital resources. Though TrustZone and SGX use different design principles. SGX adopts peer-to-peer (P2P) model and executes secured codes in private enclaves created by corresponding applications. The application and its private enclave can communicate with each other. Compared with SGX, existing TrustZone-based solutions commonly adopts the client-server (CS) model, and executes secured code in a common secure world. However, existing TrustZone-based solutions lack of strong security and openness: (1) the trusted applications (TA) share the same isolation environment, which leads to weak isolation between TAs, (2) and client applications (CA) in the normal world can only have one-way access to services provided by the secure world. That means TA cannot access the service provided by the CA, causing vendor needs to write more codes to complete TA's function and increases the TEE's attack surface. Therefore, existing TrustZone-based solutions cannot meet the strong security and openness requirements of cloud computing, artificial intelligence and blockchain technologies. In order to solve the aforementioned problems, we propose a user-level enclave protection scheme based on TrustZone. Our scheme has two major advantages compared with previous TrustZone-based solutions. Firstly, we implement the outcall function to enable the secure world to get the service provided by the normal world. Secondly, we set up security interrupt monitoring and interface encryption mechanisms to provide enclave-level isolation protection for TAs. Our evaluation results show that: (1) this scheme can effectively resist attacks on the user code and the interaction process between the secure world and the normal world. (2) this scheme has only 10% performance loss and achieved good operating efficiency.