Making good on its promise, AMD has deployed new patches to the Linux kernel to mitigate the potential security risk with the Predictive Store Forwarding (PSF) feature. Linux publication Phoronix spotted five patches that allow users to disable Predictive Store Forwarding if security is a concern.
Predictive Store Forwarding is a feature baked into AMD's Zen 3 processors that boosts code execution performance by predicting the relationship between loads and stores. In AMD's whitepaper, the chipmaker exposed the benefits and security complications with Predictive Store Forwarding. The vulnerability is similar to Spectre v4 that affected Intel processors. We reached out to AMD about the feature, and the chipmaker responded with this statement:
"AMD recommends leaving the feature enabled. We do however outline methods to disable PSF if desired."
Software that uses "sandboxing" is more susceptible to the exploit, which is why AMD gives users the power to turn off Predictive Store Forwarding. As Phoronix noted, Predictive Store Forwarding is enabled by default even on the patched Linux kernel. The Linux publication shared two ways to disable Predictive Store Forwarding: You can do so through the Spectre v4 mitigation control or implement the nopsfd parameter boot option.
Predictive Store Forwarding's job is to improve performance, so you might wonder if it presents a significant performance hit. Fortunately, it doesn't. Phoronix conducted a plethora of tests before AMD's patches and discovered performance deltas that were less than a half percent.