Six Years of Rowhammer: Breakthroughs and Future Directions

  • Stefan Saroiu, Microsoft

This talk presents the work done over the past six years as part of Project STEMA at Microsoft. STEMA stands for Secure, Trusted, and Enhanced Memory for Azure. We discuss our journey in understanding Rowhammer and our methodology for determining whether cloud servers are vulnerable to these attacks. We also explain why Rowhammer is a significant concern, particularly in the context of nation-state attacks, and how this led us to develop a pragmatic solution called Panopticon. We then introduce Panopticon, an in-DRAM Rowhammer defense that is cost-effective and requires no hardware changes beyond DRAM itself. Unlike previous solutions that monitor Rowhammer in SRAM or CAM memories, Panopticon is the first to implement monitoring within the DRAM fabric. Combined with its alert system, Panopticon has the potential to address Rowhammer once and for all. Panopticon’s approach has caught the attention of industry, leading to the development of Per-Row Activation Counting (PRAC), a groundbreaking Rowhammer defense that will soon be widely deployed in most, if not all, DRAM. In the final part of our talk, we present a brief technical deep dive into PRAC. While PRAC marks a significant advance in DRAM security, its specification leaves some questions unanswered and exposes potential gaps and challenges. This presents a huge opportunity for the research community to address these issues.

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