The first three generations of EPYC processors of AMD exposed CacheWarp vulnerabilities, affecting the security of virtual machine memory encryption.

Thanks to CTOnews.com netizen OC_Formula for the clue delivery! CTOnews.com, November 17, according to the German media ComputerBase, researchers at AMD and the University of Gratz in Austria have revealed a new vulnerability in AMD EPYC processors called CacheWarp or CVE-2023-20592, involving first-to third-generation EPYC processors.

This vulnerability takes advantage of the unique CTOnews.com Secure Encrypted Virtualization (SEV) feature of EPYC processors, which is designed to improve the security of virtual machines by encrypting the memory of each virtual machine with a key, but this function, which is supposed to enable it to resist hackers, gives CacheWarp a chance.

CacheWarp is triggered by using the INVD instruction to clear CPU's cache so that CPU stores obsolete data in system memory or RAM, and then CPU reads the data from RAM and "thinks" that the data is new.

According to reports, the key data read by CPU is the verification value-it must be 0 to be successfully verified. The only way to verify that the value is 0 should have been to enter the correct key, but the initial value of this value is also 0, resulting in a vulnerability.

Although this vulnerability affected the first three generations of EPYC processors, only the third generation of EPYC processors (codenamed Milan) received official microcode patches. AMD explained that the first two generations of processors did not require patches, adding that "for them, the features related to secure encryption virtualization are not used to protect the memory integrity of virtual machines."