The Rowhammer vulnerability poses an increasing challenge with newer generations of DRAM and aggressive technology scaling. Existing mitigation techniques, such as Graphene, Twice, and Hydra, primarily rely on tracking activation counts for each row and issuing refreshes when a row reaches a predefined tracking threshold. However, these methods have inherent limitations, including inefficiencies in identifying rows genuinely at risk of bit flips. In this paper, we propose a novel framework called Rowhammer Vulnerability Count (RVC), which shifts the focus from activation count tracking to evaluating a row's actual vulnerability to bit flips. By selectively issuing refreshes only to rows on the verge of experiencing bit flips, RVC drastically reduces unnecessary refresh operations. We also demonstrate that prior works have incorrectly set tracking thresholds, leading to security flaws. Our evaluation shows that RVC achieves 95 - 99.99% improvement in mitigation induced refreshes when compared to Graphene, with no additional space overhead. Furthermore, RVC improves energy efficiency and reduces average LLC latency by up to 76.91%, making it a highly efficient and scalable solution for addressing Rowhammer in modern DRAM systems. These findings establish RVC as a superior approach for preventing Rowhammer, outperforming existing methods in both accuracy and efficiency.

翻译：随着新一代DRAM及激进工艺缩放的推进，Rowhammer漏洞带来的挑战日益严峻。现有缓解技术（如Graphene、Twice和Hydra）主要依赖追踪每行激活次数，并在行达到预设追踪阈值时发出刷新指令。然而，这些方法存在固有缺陷，例如难以准确识别真正面临比特翻转风险的行。本文提出一种名为Rowhammer脆弱性计数（RVC）的新型框架，将焦点从激活次数追踪转向评估行实际遭受比特翻转的脆弱性。通过仅对濒临比特翻转的行选择性执行刷新操作，RVC大幅减少了不必要的刷新行为。我们还证明，先前工作中设定的追踪阈值存在错误，导致安全隐患。评估结果表明，与Graphene相比，RVC将缓解引发的刷新操作降低了95%-99.99%，且无需额外空间开销。此外，RVC将能效提升最多76.91%并降低平均LLC延迟，使其成为应对现代DRAM系统中Rowhammer问题的高效可扩展解决方案。这些发现确立了RVC在准确性和效率方面均优于现有方法的Rowhammer防御技术。