AMD reports that AMD Zen 3 processors are vulnerable to side-channel attacks and advises owners of processors on this architecture to disable the Predictive Store Forwarding (PSF) feature, which improves performance if they intend to use the machine for sensitive operations. This is because this feature is vulnerable to side-channel attacks like Specter.This function is associated with a proactive (or speculative) mechanism of instruction execution, that is, the CPU performs several alternative operations in advance to speed up the work, and then discards unnecessary “predicted” data.
“In typical code, PSF provides performance gains by assuming the result of loading and allowing later instructions to start executing earlier than they otherwise would. In most cases, the PSF prediction is accurate. However, there are times when the forecast can be inaccurate and cause incorrect CPU assumptions”, — AMD engineers describe PSF technology.
The Record cites a specialist from the Graz University of Technology Daniel Gruss, who discovered that AMD PSF can be vulnerable to various side-channel attacks, which have been developed over the years, it is enough to recall Specter, Meltdown, Specter-NG, ZombieLoad, Foreshadow, RIDL, Fallout, LVI and so on.
“Overall, PSF is an extension of the simpler store-to-load forms that have been previously used for Specter attacks. Thus, the PSF allows new variants of Specter-STL (or Specter-v4) attacks to be exploited. PSF adds another opportunity for the attacker to directly get values from the victim’s domain if very specific gadgets are running in the victim’s domain”, — Gruss explained.
While some of the previous attacks occasionally affected AMD and Arm processors, most of the attacks affected the Intel processor, as the company first used speculative execution to improve performance, far ahead of its competitors.
AMD has already admitted that researchers may be right and that PSF can expose customers to various risks. As a result, the company recommends users to use hardware rather than software sandboxing or completely disable PSF.
Let me also remind you that we wrote that Microsoft presented resistant to attacks Pluton processor.
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