# SoftTRR: Protect Page Tables Against RowHammer Attacks using Software-only Target Row Refresh

**Authors:** Zhi Zhang, Yueqiang Cheng, Minghua Wang, Wei He, Wenhao Wang, Nepal Surya, Yansong Gao, Kang Li, Zhe Wang, Chenggang Wu  
**arXiv:** [2102.10269](https://arxiv.org/abs/2102.10269)  
**Date:** 2021-02-20  
**Summary page:** https://www.summarizepaper.com/fr/paper/2102.10269v1/

## Abstract

Rowhammer attacks that corrupt level-1 page tables to gain kernel privilege are the most detrimental to system security and hard to mitigate. However, recently proposed software-only mitigations are not effective against such kernel privilege escalation attacks. In this paper, we propose an effective and practical software-only defense, called SoftTRR, to protect page tables from all existing rowhammer attacks on x86. The key idea of SoftTRR is to refresh the rows occupied by page tables when a suspicious rowhammer activity is detected. SoftTRR is motivated by DRAM-chip-based target row refresh (ChipTRR) but eliminates its main security limitation (i.e., ChipTRR tracks a limited number of rows and thus can be bypassed by many-sided hammer). Specifically, SoftTRR protects an unlimited number of page tables by tracking memory accesses to the rows that are in close proximity to page-table rows and refreshing the page-table rows once the tracked access count exceeds a pre-defined threshold. We implement a prototype of SoftTRR as a loadable kernel module, and evaluate its security effectiveness, performance overhead, and memory consumption. The experimental results show that SoftTRR protects page tables from real-world rowhammer attacks and incurs small performance overhead as well as memory cost.