The Avatar Cache: Enabling On-Demand Security with Morphable Cache Architecture

2026-02-06

AI Summary

Shared last-level caches in multicore systems are vulnerable to cross-core contention and occupancy-based side-channel attacks, yet existing secure cache designs struggle to balance area overhead, performance, and scalability, hindering practical deployment. This work proposes Avatar, a morphable cache architecture that dynamically switches among three modes: insecure, randomized secure (Avatar-R), and partitioned secure (Avatar-P). Avatar uniquely enables on-demand security activation without OS support, incurring only 1.5% storage overhead and 0.2% performance degradation in Avatar-R mode while achieving a security strength of one collision every 10³⁰ years. Avatar-P incurs merely 3% performance overhead—significantly outperforming prior partitioning schemes—and the insecure mode retains native performance and energy efficiency.

Technology Category

• Machine Learning: Hardware-aware ML
• Cognitive Modeling & Cognitive Systems: Agent Architectures
• Application Domains: Security

Application Category

• Security and Privacy: Large-scale security measurements
• User Modeling, Personalization and Recommendation: Attacks and countermeasures in recommendation systems
• Responsible Web: Data and user privacy-enhancing technologies for the Web

Abstract

The sharing of the last-level cache (LLC) among multiple cores makes it vulnerable to cross-core conflict- and occupancy-based attacks. Despite extensive prior work, modern processors still employ non-secure set-associative LLCs. Existing secure LLC designs broadly fall into two categories: (i) randomized and (ii) partitioned. The state-of-the-art randomized design, Mirage, mitigates conflict-based attacks but incurs significant area overhead (20% additional storage) and design complexity. Partitioned LLCs mitigate both conflict- and occupancy-based attacks, but often suffer from large performance overheads (on average over 5% and up to 49%), require OS support in set-based schemes, or face scalability issues in way-based schemes. These factors pose major obstacles to the industrial adoption of secure LLCs. This paper asks whether strong LLC security can be achieved with minimal changes to a conventional set-associative LLC, enabling security only when needed while preserving low performance, power, and area overheads. We propose Avatar, a secure and morphable LLC that supports three modes: non-secure (Avatar-N), randomized secure (Avatar-R), and partitioned secure (Avatar-P), and can switch dynamically between them. Avatar closely resembles a conventional set-associative LLC, facilitating industrial adoption. Avatar-R introduces extra invalid entries and leverages high associativity to provide a strong security guarantee with little capacity loss, achieving only one set-associative eviction per $10^{30}$ years, while incurring 1.5% storage overhead, a 2.7% increase in static power, and a 0.2% slowdown over a 16~MB baseline. Avatar-P mitigates both conflict- and occupancy-based attacks with only a 3% performance overhead, substantially outperforming prior way-based partitioned LLCs. When security is unnecessary, Avatar switches to Avatar-N to maximize performance and energy efficiency.

Problem

• last-level cache
• security
• conflict-based attacks
• occupancy-based attacks
• cache architecture

Innovation

• morphable cache
• secure LLC
• on-demand security
• conflict-based attacks
• partitioned cache