The Specter vulnerability that burned Intel’s head is now on the side of AMD Ryzen Zen 3 processors.
Three years ago, many Intel processors had serious problems due to the Specter vulnerability. Now, AMD Ryzen Zen 3 processors also face a Specter-like vulnerability. In the company’s report, it is stated that the new technology called Predictive Store Forwarding (PSF), introduced by AMD in Zen 3-based Ryzen and EPYC processors, provides an environment for this vulnerability. PSF works by predicting the relationship between loads and repositories, which improves code execution performance, and its predictions are mostly accurate. On the other hand, in the case of a false prediction, the result is false processor speculation.
Architects of AMD Zen processors state that the vulnerability is at the same level as Specter v4. It is also stated that it is possible for the repository / payload pair to become addicted for a while, but then to stop the addiction. It is shared that this can also occur if the address of the warehouse or load changes during the execution of the program.
The second source of false PSF predictions can arise if there is an alias in the PSF prediction structure. The PSF estimator is designed to monitor repositories / payload pairs according to the parts of their RIP. It seems possible that a bin / payload pair with a dependency could be aliased in the predictor with another bin / payload pair that was not. This could lead to false speculation when the second storage / load pair is executed.
AMD has not seen any exploits or any code using Predictive Store Forwarding, which is thought to be susceptible to false predictions. Therefore, the security risk is believed to be low for most applications. Although AMD admits that there are some vulnerabilities, the technology also brings performance advantages for Ryzen processors.
The company officially recommends leaving Predictive Store Forwarding (PSF) technology to achieve the best possible performance. So those who are worried about the vulnerability can disable PSF.