Cross-core data disclosure via incomplete buffer cleanup

Special register buffer data sampling in some Intel processors allows local users to infer sensitive values read on other CPU cores. A special register read refreshes only the needed portion of a shared staging buffer, leaving stale RDRAND, RDSEED, or SGX EGETKEY data that the processor copies into a core's fill buffer. Code running locally on an affected processor that is also susceptible to MFBDS or TAA can sample those stale values across cores, exposing only special-register data rather than arbitrary memory.