This question is based off of a TempleOS question here on Super User. The gist is that PS/2 support seems to be disabled from many modern BIOS’es due to a possible security flaw in the protocol. Specifically from this section on the TempleOS site explaining “Why Not More?”:
I don't stand a chance working on native hardware, anymore. I could install and run natively on hardware from about 2005-2010. It requires BIOS's being nice enough to write USB mode PS/2 legacy keyboard/mouse support. As it turns-out, sometimes the BIOS has PS/2 drivers but purposely disables them, just to be mean. The CIA and whole industry is trying to mess everything up, on purpose. Perhaps, at a point of sale in a store, a thief could hack a credit card machine. Therefore, the BIOS companies actually want it difficult to make drivers and purposely make it broken.
This seems confusing to me. The casual claim here is that PS/2 protocol is somehow weaker and more prone to—what I believe would be—man in the middle attacks on a hardware level on point of sale devices. But is that really the case with PS/2 protocol? Isn’t it the case that USB protocols are actually more risky for point of sale devices because of USB’s inherent flexibility?
Can anyone provide solid info on how/why PS/2 might be less—or more—risky to data leakage on a device level?