Half-Double: Hammering From the Next Row Over


Andreas Kogler, Graz University of Technology; Jonas Juffinger, Graz University of Technology and Lamarr Security Research; Salman Qazi and Yoongu Kim, Google; Moritz Lipp, Amazon Web Services; Nicolas Boichat, Google; Eric Shiu, Rivos; Mattias Nissler, Google; Daniel Gruss, Graz University of Technology


Rowhammer is a vulnerability in modern DRAM where repeated accesses to one row (the aggressor) give off electrical disturbance whose cumulative effect flips the bits in an adjacent row (the victim). Consequently, Rowhammer defenses presuppose the adjacency of aggressor-victim pairs, including those in LPDDR4 and DDR4, most notably TRR.

In this paper, we present Half-Double, an escalation of Rowhammer to rows beyond immediate neighbors. Using Half-Double, we induce errors in a victim by combining many accesses to a distance-2 row with just a few to a distance-1 row. Our experiments show that the cumulative effect of these leads to a sufficient electrical disturbance in the victim row, inducing bit flips. We demonstrate the practical relevance of Half-Double in a proof-of-concept attack on a fully up-to-date system. We use side channels, a new technique called BlindHammering, a new spraying technique, and a Spectre attack in our end-to-end Half-Double Attack. On recent Chromebooks with ECC- and TRR-protected LPDDR4x memory, the attack takes less than 45 minutes on average.

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@inproceedings {281352,
author = {Andreas Kogler and Jonas Juffinger and Salman Qazi and Yoongu Kim and Moritz Lipp and Nicolas Boichat and Eric Shiu and Mattias Nissler and Daniel Gruss},
title = {{Half-Double}: Hammering From the Next Row Over},
booktitle = {31st USENIX Security Symposium (USENIX Security 22)},
year = {2022},
isbn = {978-1-939133-31-1},
address = {Boston, MA},
pages = {3807--3824},
url = {https://www.usenix.org/conference/usenixsecurity22/presentation/kogler-half-double},
publisher = {USENIX Association},
month = aug,

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