The shape of the flaw seems pretty clearly described in the abstract - it's the ability to either modify the contents of the locked SMM memory regions (and so g

The shape of the flaw seems pretty clearly described in the abstract - it's the ability to either modify the contents of the locked SMM memory regions (and so get arbitrary code execution there), or trigger SMM execution of code outside the SMRAM region. Either way, SMM vulnerabilities aren't new, and the capabilities associated with them are pretty well understood - what's different here is that the vulnerability is apparently in the CPU rather than the firmware, and so everyone's affected no matter who their firmware vendor is.