Read disturbance in modern DRAM chips is a widespread phenomenon and is reliably used for breaking memory isolation, a fundamental building block for building robust systems. RowHammer and RowPress are two examples of read disturbance in DRAM where repeatedly accessing (hammering) or keeping active (pressing) a memory location induces bitflips in other memory locations. Unfortunately, shrinking technology node size exacerbates read disturbance in DRAM chips over generations. As a result, existing defense mechanisms suffer from significant performance and energy overheads, limited effectiveness, or prohibitively high hardware complexity. In this paper, we tackle these shortcomings by leveraging the spatial variation in read disturbance across different memory locations in real DRAM chips. To do so, we 1) present the first rigorous real DRAM chip characterization study of spatial variation of read disturbance and 2) propose Sv\"ard, a new mechanism that dynamically adapts the aggressiveness of existing solutions based on the row-level read disturbance profile. Our experimental characterization on 144 real DDR4 DRAM chips representing 10 chip designs demonstrates a large variation in read disturbance vulnerability across different memory locations: in the part of memory with the worst read disturbance vulnerability, 1) up to 2x the number of bitflips can occur and 2) bitflips can occur at an order of magnitude fewer accesses, compared to the memory locations with the least vulnerability to read disturbance. Sv\"ard leverages this variation to reduce the overheads of five state-of-the-art read disturbance solutions, and thus significantly increases system performance.

翻译：现代DRAM芯片中的读取干扰是一种普遍现象，并可靠地用于破坏内存隔离——构建稳健系统的基本基石。RowHammer和RowPress是DRAM中读取干扰的两种实例，反复访问（锤击）或保持激活（按压）同一内存位置会导致其他内存位置发生位翻转。不幸的是，随着工艺节点尺寸的缩小，DRAM芯片的读取干扰问题逐代加剧。因此，现有防御机制面临显著的性能和能耗开销、效果有限或硬件复杂度过高等缺陷。本文通过利用真实DRAM芯片中不同内存位置之间读取干扰的空间变化来弥补这些不足。为此，我们：1）首次对读取干扰的空间变化进行了严格的真实DRAM芯片特征研究；2）提出Svård——一种新机制，可根据行级读取干扰特征动态调整现有解决方案的激进程度。我们对代表10种芯片设计的144块真实DDR4 DRAM芯片进行的实验特征分析表明，不同内存位置对读取干扰的脆弱性存在显著差异：在读取干扰脆弱性最严重的内存区域中，与脆弱性最低的区域相比，1）位翻转数量可高达2倍，2）位翻转可在访问次数减少一个数量级时发生。Svård利用这一空间变化降低了五种最先进读取干扰解决方案的开销，从而显著提升了系统性能。