If you are worried about someone breaking in to your house and replacing the bootloader while leaving your drives in place I probably wouldn't use the TPM auto unlock even if in theory secure boot should be able to handle this.
But in reality that will never happen and the only actual attack you need to be worried about is junkies breaking in and flogging the drives on facebook marketplace. For which, this level of security is fine.
I run my cheap hosting box with a cleartext boot setup that uses ssh to automatically grab the key for the real root from my home server (or an alternate at my MILs house). Using FreeBSD, but similar concepts.
A previous hoster once gave me someone else's drives without wiping them. I don't want random customers snooping around on my data if a similar mistake happens with my disks.
For home use, I run without disk encryption. If I ever need to do data recovery, it's not going to be possible with encrypted disks and one point of a centralized NAS is to have stable long term storage.
> What about /boot - encrypted and tamper proof? Resists evil maid attack?
> Rabbit hole, I know, but so fascinating if you solved it all :)
Encrypting `/boot/` is the wrong thing to do. One can just replace it with something that logs the encryption key instead (and sends it off to somewhere). You actually need to verify that what you expect to be there is actually there and a encryption isn't gonna do that for you.
A reasonably secure boot chain looks roughly as follows: bootloader is checked by the UEFI (read secure-boot), bootloader chain loads a signed UKI which also uses secure boot verification (or just skip the bootloader if you only have a single kernel with no fallback), this then loads a signed dm-verity `/usr/` which brings you to the login screen. Root is just data (e.g. mounted `noexec`) and is encrypted using e.g. PCR 11 so that it only unlocks if the UKI is the one that is expected (with some other backup unlock method).
This is basically #2 of the "Design Goals" of Poetterings "Fitting everything together"[0]. It's a good read if you are looking to designing your own Linux image and are looking for some inspiration. There is ParticleOS[1] which somewhat dogfoods this kind of system, though I don't think it is anything remotely considered for a production system.
But in reality that will never happen and the only actual attack you need to be worried about is junkies breaking in and flogging the drives on facebook marketplace. For which, this level of security is fine.