Microarchitectural Side-Channel Attacks for Privileged Software Adversaries

Recent developments on hardware-based trusted execution environments, such as the Software Guard Extensions (SGX) included in recent Intel x86 processors, hold the promise of securely outsourcing sensitive computations to untrusted remote platforms. The compelling aspect of these architectures is that they aim to protect small software components, called enclaves, even against a very powerful type of root adversaries that have full control over the operating system on the target device. This thesis shows, however, that the protection offered by today's trusted execution environments is not sufficiently understood and should be nuanced in terms of microarchitectural attack surface.In the first part of this dissertation, we develop several innovative side-channel attack techniques that allow a privileged software adversary to reliably derive metadata from an enclaved execution. These results show that traditionally privileged x86 processor interfaces, such as page tables and interrupts, can be abused in new and unexpected ways to construct highly accurate side-channel oracles that reveal code and data access patterns performed by a victim enclave. In several practical attack scenarios, we furthermore demonstrate that these metadata access patterns can lead to full disclosure of application-level secrets.In the second part, we move from metadata exposure to direct data extraction in a critical new line of transient-execution attacks. These results show that current out-of-order processors fail to safeguard enclave secrets against subtle microarchitectural leakage coming from instructions that were tentatively executed before a CPU exception is raised. Building upon these insights, we demonstrate several innovative attacks that led to a full collapse of the Intel SGX ecosystem and required extensive hardware and software updates.We conclude this dissertation with a systematization of the last five years of SGX attacks, and we outline several promising defense avenues for next-generation hardened trusted execution architectures.

Publication year:2020