Arnt Gulbrandsen <a...@gulbrandsen.priv.no> wrote:

> Simon Hobson writes:
>> Not really, but I don't see any sign of that as a question in the post I was 
>> replying to !
> 
> You said secure boot's security is blown out of the water because it's 
> possible to run untrusted code under certain circumstances.

Pretty much

> IMHO it provides useful security because (absent mistakes by the owner) there 
> are many attackers who cannot make use of those circumstances.

Not really, it comes down to "anyone with physical access to your hardware" can 
fiddle with the boot process. With the ability to run an "insecure" boot 
package, you have the opportunity to interject in the process - such as capture 
your password unlocking the encrypted root volume.
Full disk encryption won't help unless it's handled by the BIOS/EFI, having 
full disk encryption done by the kernel means that (as a minimum) you need a 
volume unencrypted with a bootloader, kernel, and init filesystem.

Really, it comes down to that group of "many attackers who cannot make use of 
those circumstances" is really the same set that can't attack your boot process 
because they don't have physical access to the machine (or remote admin ability 
while it's running). In this situation, the security added by secure boot is 
roughly ... a bit of a hindrance, but no obstacle to someone who knows what 
they are doing.

The only way round that is for there to be no "insecure" signed bootloaders in 
existence. But because that situation pretty well kills "open" operating 
systems, that is not the case.

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