Attacking full-disk encryption with Inception

With Firewire, the device sets up and starts the DMA

so the exploit DMA on other devices, you need to hack the firmware of the controller card to have it do something other than what the device driver expects it to.

But with Firewire, you only need to hack the firmware of the device you are plugging in (and since you can completely control that device, this is rather easy)

In terms of risk, Firewire is more like exposing the PCI bus for external things to plug into.