x86: Register File Data Sampling

ISSUE DESCRIPTION

Intel have disclosed RFDS, Register File Data Sampling, affecting some Atom cores.
This came from internal validation work. There is no information provided about how an attacker might go about inferring data from the register files.
For more details, see: <a href=“https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/advisory-guidance/register-file-data-sampling.html”>https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/advisory-guidance/register-file-data-sampling.html</a>

IMPACT

An attacker might be able to infer the contents of data held previously in floating point, vector and/or integer register files on the same logical processor, including data from a more privileged context.
Note: None of the vulnerable processors support HyperThreading, so there is no instantaneous exposure of data from other threads.

VULNERABLE SYSTEMS

Systems running all versions of Xen are affected.
RFDS is only known to affect certain Atom processors from Intel. Other Intel CPUs, and CPUs from other hardware vendors are not known to be affected.
RFDS affects Atom processors between the Goldmont and Gracemont microarchitectures. This includes Alder Lake and Raptor Lake hybrid client systems which have a mix of Gracemont and other types of cores.