[plug] SED Trap for young players

[Brad Campbell]

I have a "main server". It runs the household and my business, is on a big UPS and is generally "hands-off".
It boots off a pair of SATA drives, loads the initramfs which them unlocks the 2 NVME drives that hold the OS and most of the data.
These drives are SED encrypted and so need to be unlocked after a power cycle.

Recently I replaced one of the drives. 

Fast forward a couple of months when I went to replace the PSU and on boot was greeted with a UEFI "Enter the password for this drive" screen.
Had to manually escape a couple of times before it warned me the password was wrong and the drive was still locked. That meant anytime the
machine power cycled it was going to need manual intervention to bring it back up. Not acceptable. So I rifled through all the BIOS/EFI settings
and could not figure out how to disable this.

When I first set SED up a decade ago, I just blindly followed the instructions in the FAQ.
This time I thought "Why do I need to enable the shadow MBR, I don't use it". I set the drive up and off we went. I enabled locking, unlocked and rebooted.
Everything came up as you'd expect so I thought nothing more of it. I did *not* check a hard power cycle, because it has always "just worked".

Turns out if the UEFI sees the shadow MBR it thinks "Well, there's something there that will unlock the drive, so I won't worry". If not however
then you get the boot blocking "enter the password" screen.

Easy enough, just sedutil-cli --setMBREnable on and the problem is solved.

Just in case anyone ever hits it.