In early 2015 news broke that the NSA was installing firmware backdoors in many hard drives. I was wondering, if there was a BIOS and Hard Drive backdoor how well would full disk encryption protect you, if at all.
This article describes how a certain hacking tool, which could be deployed by a hard-drive's firmware-based backdoor, can be used to grab crucial information from RAM and then store it on a small area on the firmware, to be retrieved later in order to aid in decrypting the drive.
For instance, if using bitlocker, such crucial information might be any file called "Bitlocker Recovery Key*" (the user is prompted to save such file(s) when enabling encryption). A more sophisticated technique would be to get the surrogate key from memory, in the same principle as a cold boot attack.