If I remember correctly, not long ago someone posted here about a cheat using DMA to modify the display buffer of a shooter. I'm in a hurry but I'll look it up later.
Well, with DMA, one can do pretty much anything. Doesn’t Thunderbolt (which is PCIe and hence has DMA) have this problem? As in, couldn’t a rouge TB peripheral siphon your data?
Thunderbolt & Firewire before it. DMA to external devices is powerful but the feature also means you expose a bus that wasn't originally conceived to be read by malicious agents.