Exploiting System Management Mode with a very very very very very very very long interrupt. Overview It turns out that you can break SMM — the secure, ultra privileged execution environment running invisibly in the background of every x86 CPU — with nothing more than an obscenely long-running machine instruction. SMM requires that all cores are either in SMM or out of SMM at the same time. Its security model doesn't work without this - when one thread enters SMM, it makes all the others enter too. To break this, all we need is someone too busy to notice they're supposed to join SMM.…