Almost unfixable “Sinkclose” bug affects hundreds of millions of AMD chips

Article note: It's always the add on security/management features. If you already have kernel access in any recent AMD box, you can use some (necessary for compatibility) memory remapping features to make the SMM (basically maximum-privilge firmware) read code from memory written by the OS... which can give you a firmware-resident foothold that will persist even through OS reinstalls.

Security flaws in your computer's firmware, the deep-seated code that loads first when you turn the machine on and controls even how its operating system boots up, have long been a target for hackers looking for a stealthy foothold. But only rarely does that kind of vulnerability appear not in the firmware of any particular computer maker, but in the chips found across hundreds of millions of PCs and servers. Now security researchers have found one such flaw that has persisted in AMD processors for decades, and that would allow malware to burrow deep enough into a computer's memory that, in many cases, it may be easier to discard a machine than to disinfect it.

At the Defcon hacker conference, Enrique Nissim and Krzysztof Okupski, researchers from the security firm IOActive, plan to present a vulnerability in AMD chips they're calling Sinkclose. The flaw would allow hackers to run their own code in one of the most privileged modes of an AMD processor, known as System Management Mode, designed to be reserved only for a specific, protected portion of its firmware. IOActive's researchers warn that it affects virtually all AMD chips dating back to 2006, or possibly even earlier.