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Upmem Nails RowHammer

June 22, 2021

Author: Tom R. Halfhill

Although human memory is notoriously faulty, computer memory requires perfection. We hardly notice a few wayward synapses, but a single-bit error in DRAM can crash a program or even a whole computer. Error-correction codes (ECC) protect servers and other mission-critical systems from random “soft errors” that flip a DRAM bit cell from one to zero or vice versa, but larger errors remain a problem. In recent years, a deliberate attack called RowHammer is playing havoc with DRAM chips and the computers that rely on them.

First documented in 2014, RowHammer deliberately flips bits by rapidly and repeatedly accessing specific DRAM rows. Although it’s unable to control the flips to write malicious code into memory, it can overwhelm ECC protection, crashing the affected program or forcing the entire system to reboot. In its simplest form, RowHammer mounts a denial-of-service (DoS) attack. In more-sophisticated assaults, it can trigger a fault that gives the attacker elevated system privileges or access to another user’s virtual partition on a shared server. In other words, it’s potentially catastrophic.

Various countermeasures have been only somewhat effective or costly in lost performance and power. Now, a French startup, Grenoble-based Upmem, claims to have a defense that’s economical and completely effective. It has patented the technique and is offering it to DRAM manufacturers as licensable intellectual property (IP). The catch is that the solution, called Silver Bullet, requires modification of future DRAM-chip designs. The modifications are minimal but can’t be added to existing DRAMs.

The upside is that Silver Bullet doesn’t require the industry to modify memory controllers, create new DDR protocols, revise operating systems, or adopt nonstandard manufacturing technology. If DRAM makers license the IP, their new chips could be available in less than a year.

Subscribers can view the full article in the Microprocessor Report.

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