Protecting enclaves from side-channel attacks through physical isolation

Abstract

The digital world is taking an increasingly crucial role in our lives. Digital systems control our calendars, how we gain access to our devices and even the vehicles we use for transportation. It is therefore no surprise that security solutions like trusted execution environments (TEEs) have been introduced in many systems ranging from small embedded networking devices to large server racks. One of the main challenges of this ever growing functionality is keeping the trusted computing base (TCB) small and manageable. Enclave systems are a way to do exactly that: they allow applications to run on the same system as a rich operating system (OS) while ensuring the confidentiality and integrity of enclave data.

In this thesis I explore the difficulty in protecting enclaves from side-channel attacks in the face of privileged software. I propose a threat model, a methodology to analyze side channels and a new enclave system that adheres to this threat model. Due to the complexities of modern superscalar processors, I conclude that it is undesirable to run enclaves on the same cores as untrusted software due to the performance degradation this would have on regular applications. My new enclave system uses a heterogeneous multi-core processor to physically isolate enclaves on secure cores while regular applications run on fast cores. I show that this system works with a conventional OS by implementing a Linux driver that facilitates management of enclaves and communication between untrusted applications and enclaves. The enclave subsystem only requires a small TCB: a trusted management shim to interface the Linux driver with the enclave hardware. I evaluate hardware implementation approaches in simulation and on a field-programmable gate array (FPGA). The evaluation shows that this system is reasonable in communication overhead, memory footprint, runtime and hardware area. Thus, physical isolation is a feasible way to protect enclaves from side-channel attacks in modern enclave systems.