Tavis Ormandy discovered that under specific microarchitectural
circumstances, a vector register in "Zen 2" CPUs may not be written to 0 correctly. This flaw allows an attacker to leak register contents across concurrent processes, hyper threads and virtualized guests.
The initial microcode release by AMD only provides updates for second generation EPYC CPUs: Various Ryzen CPUs are also affected, but no
updates are available yet. Fixes will be provided in a later update once
they are released.