The patch wouldn’t stop users running microcode for older CPUs on Linux but would flag them as vulnerable.
Intel engineer Dave Hansen has sparked a “Microcode Revision Discussion” regarding a proposed Linux patch on the kernel mailing list.
This new feature would report outdated microcode through the existing sysfs vulnerabilities reporting system. Specifically, it would create a new file at /sys/devices/system/cpu/vulnerabilities/old_microcode.
The patch would introduce a X86_BUG_ OLD_MICROCODE flag to mark CPU microcode as vulnerable if outdated.
This lies at the heart of Hansen’s proposed changes, as he states in the preamble to the online discussion: “You can’t practically run old microcode and consider a system secure these days. So, let’s call old microcode what it is: a vulnerability.”