AMD 16h processor microcode - locked instructions vs write-combined memory: Interaction between locked instructions

Impact

Interaction between locked instructions and write-combined memory types hangs the system, reachable from an unprivileged local application. A tenant can wedge the whole machine with a small crafted program - no privilege needed, no recovery short of a hard reset. Included for completeness on legacy AMD hardware; it is the archetype of the 'any tenant can halt the node' class that keeps recurring in CPU errata.

Who can reach it

Local, unprivileged. Any process on the machine, including inside a container.

What to do

Fixed by a BIOS/microcode update carrying the erratum 793 workaround. Affects AMD 16h family processors, long out of production - if you have any of these in a fleet, the realistic answer is that they are past firmware support and should be retired rather than patched.

References