According to AMD’s own security analysis, Zen 3 processors (Ryzeny 5000, etc.) contain a potential security hole in the Predictive Store Forwarding (PSF) implementation. It is theoretically possible to exploit this feature of the CPU for a Specter attack.
Predictive Store Forwarding is a technique that provides higher CPU performance to the point where the processor tries to estimate (predict) the dependencies between load and store instructions and execute the corresponding instructions speculatively. AMD researchers have concluded that their implementation of PSF in the CPU may be susceptible to Specter V4 (Speculative Store Bypass) attacks, respectively. running untrusted code inside the sandbox.
AMD does not currently know of any code that would be risky for PSF, considers the risk of misuse of PSF mechanisms to be small, but publishes all findings and adds recommendations to deactivate Predictive Store Forwarding (more in PDF). It is not necessary to turn off the PSF if the Specter V4 (SSB) fix is already applied, but you can only deactivate the pure PSF – this can also be done after individual CPU threads. AMD is currently ready to implement patches for Linux using the new kernel option, but they are not yet in the kernel.
For most users, an active PSF should not pose a risk.
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