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arXiv · 2505.10111

When Mitigations Backfire: Timing Channel Attacks and Defense for PRAC-Based RowHammer Mitigations

Jeonghyun Woo·Joyce Qu·Gururaj Saileshwar·Prashant J. Nair
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Abstract

Per Row Activation Counting (PRAC) has emerged as a robust framework for mitigating RowHammer (RH) vulnerabilities in modern DRAM systems. However, we uncover a critical vulnerability: a timing channel introduced by the Alert Back-Off (ABO) protocol and Refresh Management (RFM) commands. We present PRACLeak, a novel attack that exploits these timing differences to leak sensitive information, such as secret keys from vulnerable AES implementations, by monitoring memory access latencies. To counter this, we propose Timing-Safe PRAC (TPRAC), a defense that eliminates PRAC-induced timing channels without compromising RH mitigation efficacy. TPRAC uses Timing-Based RFMs, issued periodically and independent of memory activity. It requires only a single-entry in-DRAM mitigation queue per DRAM bank and is compatible with existing DRAM standards. Our evaluations demonstrate that TPRAC closes timing channels while incurring only 3.4% performance overhead at the RH threshold of 1024.

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Jeonghyun Woo, Joyce Qu, Gururaj Saileshwar, Prashant J. Nair. 2025-05-15. When Mitigations Backfire: Timing Channel Attacks and Defense for PRAC-Based RowHammer Mitigations. https://arxiv.org/abs/2505.10111

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