May 28, 2023

AMD published a document detailing the vulnerability of the Zen 3 generation processors. It was revealed that one of the architecture elements was susceptible to so-called side-channel attacks, the prominent representatives of which were the Specter and Meltdown vulnerabilities of Intel processors. There were no such problems with AMD processors, but now they have appeared and hit the newest CPUs on the Zen 3 architecture. What happened?

One of the important elements to speed up processors’ work on the Zen 3 architecture is the Predictive Store Forwarding (PSF) prediction engine. This is a process of speculative execution of instructions when the processor logic tries to predict the result of loading and starts executing instructions that are far in the queue in advance. Typically, the prediction accuracy is very high, explaining AMD, making it possible to increase computing performance significantly.

Since the data is processed with predictions in mind, there is still room for error. In such cases, the data must be discarded, but, as in the Specter attacks, the malicious code opens up the possibility of gaining unauthorized access to intermediate results of calculations, even in a protected memory area. In particular, according to AMD, the attack on PSF is in many ways similar to the Specter V4 (Speculative Store Bypass) attack.

It should be said that the company’s specialists are not aware of any attacks on Zen 3 processors using a vulnerability in the PSF. Therefore, AMD considers the risk of this vulnerability below. Most users do not recommend disabling the PSF function because this will reduce system performance.

At the same time, the company is working on patches to disable Predictive Store Forwarding conveniently. It is claimed that a patch for Linux has already been created. There are likely to be patched for Windows in the pipeline. .

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