According to a security white paper released by AMD this week, the company conducted an in-depth analysis of the “predictive store forwarding” (Predictive Store Forwarding) feature introduced by the and finally confirmed a potential side-channel attack. Phoronix pointed out that AMD will allow customers to disable this feature to prevent susceptibility to attacks similar to the “Spectre” processor security vulnerabilities.
As per the official description, PSF aims to try to predict the relationship between load and store to improve processor performance, and it can speculatively execute instructions based on related load results.
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Although the prediction can be hit to a large extent, it can still lead to erroneous CPU speculations. AMD researchers pointed out that the impact of incorrect PSF predictions is similar to that of Spectre V4. This concern becomes especially obvious when executing untrusted code in a sandbox/isolated environment.
Although AMD has not noticed any impact codes used in the wild, and the risk estimate of PSF is “maybe extremely low”, there is still a need to allow PSF to be closed and provide relevant guidance.
Based on this, when deploying Spectre V4 / SSB mitigation measures, AMD will also disable the “predictive store and forward” (PSF) behavior of Zen 3 processors.
At present, AMD officials are ready to deploy Linux patches, but at the time of writing, the company seems to have not disclosed it to the outside world.
