SPOILER: Speculative Load Hazards Boost Rowhammer and Cache Attacks (1903.00446v2)

Abstract: Modern microarchitectures incorporate optimization techniques such as speculative loads and store forwarding to improve the memory bottleneck. The processor executes the load speculatively before the stores, and forwards the data of a preceding store to the load if there is a potential dependency. This enhances performance since the load does not have to wait for preceding stores to complete. However, the dependency prediction relies on partial address information, which may lead to false dependencies and stall hazards. In this work, we are the first to show that the dependency resolution logic that serves the speculative load can be exploited to gain information about the physical page mappings. Microarchitectural side-channel attacks such as Rowhammer and cache attacks like Prime+Probe rely on the reverse engineering of the virtual-to-physical address mapping. We propose the SPOILER attack which exploits this leakage to speed up this reverse engineering by a factor of 256. Then, we show how this can improve the Prime+Probe attack by a 4096 factor speed up of the eviction set search, even from sandboxed environments like JavaScript. Finally, we improve the Rowhammer attack by showing how SPOILER helps to conduct DRAM row conflicts deterministically with up to 100% chance, and by demonstrating a double-sided Rowhammer attack with normal user's privilege. The later is due to the possibility of detecting contiguous memory pages using the SPOILER leakage.

• The paper demonstrates that false dependency hazards in speculative loads reveal physical page mappings essential for efficient microarchitectural attacks.
• It shows that exploiting the undocumented 1MB aliasing effect drastically enhances eviction set construction for Prime+Probe attacks and enables deterministic DRAM row conflicts for Rowhammer.
• The study emphasizes that robust hardware-level mitigations are required, as these exploits can bypass traditional software protections even in sandboxed environments.

An Analysis of the SPOILER Attack: Advancements in Microarchitectural Exploitation

In the paper "SPOILER: Speculative Load Hazards Boost Rowhammer and Cache Attacks," the authors introduce an incisive examination of the previously underexplored speculative load hazards in modern microarchitectural practices. The focus of the paper revolves around speculative execution, particularly how speculative loads contribute to effective performance by allowing memory operations to proceed out-of-order; however, this very mechanism is identified as susceptible to the novel side-channel exploit, coined by the authors as SPOILER.

Key Contributions and Methods

The paper makes several notable contributions to the domain of microarchitectural security. It primarily demonstrates the revelation of a previously undisclosed leakage source stemming from false dependency hazards during speculative load operations. This leakage uncovers physical page mapping information crucial for conducting efficient microarchitectural attacks such as Rowhammer and cache attacks. The SPOILER exploit accelerates the reverse engineering of virtual-to-physical mappings, surpassing existing methodologies by a factor of 256, applicable even across sandboxed environments like JavaScript.

By leveraging this leakage, SPOILER transforms the search for eviction sets and enhances the classic Prime+Probe cache attacks, facilitating faster eviction even within restricted environments. Additionally, the authors achieve deterministic DRAM row conflicts fundamental for executing potent Rowhammer attacks, demonstrating near 100% success rates and illustrating a feasible double-sided Rowhammer attack under regular user privileges.

Empirical Analysis and Results

The empirical analysis is thorough, utilizing hardware performance counters (HPCs) to correlate speculative execution anomalies with microarchitectural events. Notably, SPOILER capitalizes on the undocumented 1MB aliasing behavior, resulting in distinct maximum latency peaks during speculative loads that arise evidently from Intel processors like Kaby Lake, Skylake, among others. This realization highlights a critical vulnerability embedded in Intel’s memory disambiguation and dependency resolution logic.

Further, the paper explores JavaScript-based scenarios, typically constrained by the absence of certain assembly level instructions and accurate timers. SPOILER circumvents these restrictions by exploiting latency discrepancies, thus enhancing previous JavaScript-based attack techniques and measuring eviction set creation efficacy across various system configurations.

Implications for Microarchitectural Security

Theoretically, SPOILER opens avenues for refining our understanding of speculative execution vulnerabilities. It underscores an inherent trade-off between performance optimization and security, vividly illustrating how speculative techniques once conceived to augment efficiency now simultaneously expand the attack surface. The paper proves significant, not merely due to its direct implementation ease from user space without administrative rights but as it elevates existing attacks and introduces the potential for fresh ones by disclosing intricate microarchitectural information.

From a practical standpoint, the implications ripple across both hardware manufacturers and software engineers, demanding reconsideration of current speculative design architectures. While software mitigations can introduce partial ameliorations, addressing the heart of this leakage necessitates hardware-level interventions—likely at some performance cost—which challenge conventional performance-security equilibria.

Future Prospects in Microarchitectural Research

Looking forward, the SPOILER attack underlines a vital research trajectory aimed at exploring speculative vulnerabilities beyond the current landscape of side channel exploits. A prolific field emerges that requires rigorous inquiries into sealed speculative behaviors and undocumented microarchitectural intricacies—efforts that will significantly inform the designs of next-generation processors that preempt similar threats.

This research piece serves not only as a technical exposition of speculative vulnerabilities but also calls upon researchers and industry experts to collaboratively conceive security paradigms that inherently integrate with performance optimizations rather than retrofit post-detection solutions. The enduring task is to mediate speculation’s dual role: as an inadvertently potent enabler of microarchitectural exploits and as a catalyst for computational efficiency.