Intel processors (return predictor target sharing): Return predictor targets are shared non-transparently

Impact

Return predictor targets are shared non-transparently between contexts, giving an authorised local user an information-disclosure channel. Fixed in the same microcode wave as the 2024 return-predictor advisories.

Who can reach it

Local authorised code.

What to do

Mitigated by an Intel microcode update plus OS/hypervisor changes. Microcode for this class is normally shipped by your distribution as an early-loadable image, so you can deploy it with a package update and a reboot without waiting for an OEM BIOS release - that distinction is the difference between a week and a quarter. Verify after reboot by reading /sys/devices/system/cpu/vulnerabilities/ rather than assuming the package took effect.

References