Technology

As the chips shrink, it becomes more difficult to stop Rowhammer attacks


In 2015, researchers Google has a troubling discovery: a data theft technology known as “Rowhammer”, which was previously seen as a theoretical concern. Can be exploited In real world conditions. Now a different group of computer scientists at Google has shown that the problem has been exacerbated, thanks in part to improvements in how the chips are designed.

Rowhammer is a physical hacking technology that manipulates the electrical charge in computer memory chips (known as DRAM) to corrupt or steal data. In an attack, hackers repeatedly run the same program on a “row” of DRAM transistors to “hammer” that row until electricity leaks into the adjacent row. When done in a targeted fashion, this leakage can actually flip a bit in the next row of transistors from 1 to 0 or vice versa. By strategically flipping enough pieces, the attacker can begin to manipulate the target system and gain a digital foothold.

In the years that followed A native 2014 Rowhammer research, chip makers added mitigations that monitor adjacent rows for potentially suspicious behavior. But as the chips continue to be minimized, the ripple effect of knocking a particular row can flip the bits in two or more rows away. I’m thinking of Gallagher smashing a watermelon. You can protect the audience’s front by giving them all plastic gowns. But if it swayed hard enough, and the crowd was tight enough, the crust and core could come into contact with faces two or three rows deep.

Researchers He called it their attack “Half-Double,” he noted, and noted that this technology was not practical on older generations of DRAM as the transistor rows were slightly spaced. All the rest of Moore’s Law Transistors pack together more densely than ever, although the risk of spreading in Rowhammer attacks is increasing.

“This is the result of miniaturization,” Google researchers told WIRED in a written response to the questions. “In our trials with older DDR4 chips, this technology has not been successful. We are releasing this research today to further understand this threat. We hope this leads to further discussions about mitigations that are both long-lasting and effective.”

Google disclosed its findings to the semiconductor trade organization, JEDEC, which it has Issued Two Reducing the downtime. The researchers coordinated with other industry partners as well as raising awareness on the issue. But the chip makers will take some time to fully understand the implications of this.

“Imagine your house is huge,” says Daniel Mugime, a postdoctoral scientist at the University of California, San Diego. Rowhammer studied And subtle architectural attacks. “If your next-door neighbor who also owns a huge house plays loud music, you will probably hear it from your house, but maybe not from three doors. But when you live in an apartment complex where the units are crammed close together, the music will annoy the neighbors in a lot. Of apartments. It’s the same idea with the density of DRAM cells and their proximity to each other. “

A complete overhaul will also require rethinking how the chips are designed, and can be applied to future generations of DRAM. To go back to the Meiji metaphor, it is easier to build a new apartment with thicker walls and insulation than to rehabilitate an existing building.

Mugime says researchers have already understood this potential risk in theory, but Google’s results, once again, show a plausible attack in the real world. “It shows it’s more practical than many people think,” he says.

This isn’t the first time that the Rowhammer attacks appear to be resolved and then returned again. Researchers at Vrije Universiteit Amsterdam have them Repeatedly Shown In the past 18 months, existing chip defenses could be defeated against traditional Rowhammer attacks. But Google’s results carry an additional caveat that advances in the size and efficiency of memory chips will likely come with new risks from Rowhammer.

These hacking techniques require skill and even some luck to launch a real targeted attack. Given that Rowhammer’s potential exposure is present in basically every computer out there, its progress deserves to be taken seriously.


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