The bootloader is signed?

What nonsense.

How would that work? If your bootloader is signed then you can go ahead and boot any OS?

Including a malicious one?

If it were that easy it would not be a problem.

All that would be required is that the Grub folks get their key out to the motherboard manufacturers and then *anybody* or *anything* could boot whatever they damn well please via grub, including a Grub loaded malware infestation.

Good lord, if you don't have a clue what you are on about then please try and refrain from commenting. All it does is spread confusion.