🤖 AI Summary
This work addresses the programming challenges and error-proneness introduced by Arm’s POE2 architecture, which employs a complex spatiotemporal permission mechanism yet lacks a unified security model. We propose the first general-purpose secure programming model tailored for POE2, abstracting away the intricacies of its spatial and temporal indexing and encapsulating hardware features such as memory protection keys, dedicated registers, and table structures. By doing so, our model significantly simplifies permission management while preserving POE2’s strong security guarantees. It naturally supports common intra-process isolation patterns used in software partitioning, enabling developers to construct secure isolated systems more efficiently and with fewer errors.
📝 Abstract
Arm Permission Overlay Extension (POE) is an intra-process isolation mechanism based on memory protection keys. This mechanism partitions virtual memory into regions whose access permissions can be reconfigured without invoking higher exception levels. Because POE does not enforce privilege separation, POE-based protection domains are applicable only as a software fault-isolation technique.
The POE2 is an isolation mechanism that substantially extends POE1. Dealing with memory protection keys, it also introduces new registers and tables that regulate the operations permitted for code executing within protection domains associated with different keys. A permission is determined by the spatial index of the executing code (i.e., the protection key associated with code), the spatial index of the accessed memory, the operation type, and a new attribute of the thread context: its temporal index.
POE2 provides stronger security guarantees than POE1, but also introduces considerable architectural complexity. Effective permissions arise from the interaction of multiple hardware components, making direct programming non-trivial and prone to subtle errors. In the paper, we present a detailed analysis of POE2 and introduce a universal programming model with a strong security model for POE2-based systems. The model abstracts the complexity of spatial and temporal indices while enabling typical patterns of partitioned software constructed using intra-process isolation.