Comment by nextaccountic

7 hours ago

here is some actual security: encrypted /boot, encrypted everything other than the boot loader (grub in this case)

sign grub with your own keys (some motherboards let you to do so). don't let random things signed by microsoft to boot (it defeats the whole point)

so you have grub in an efi partition, it passes secure boot, loads, and attempts to unlock a luks partition with the user provided passphrase. if it passed secure boot it should increase confidence that you are typing you password into the legit thing

so anyway, after unlocking luks, it locates the kernel and initrd inside it, and boots

https://wiki.archlinux.org/title/GRUB#Encrypted_/boot

the reason I don't do it is.. my laptop is buggy. often when I enable secure boot, something periodically gets corrupted (often when the laptop powers off due to low power) and when it gets up, it doesn't verify anything. slightly insane tech

however, this is still better than, at failure, letting anything run

sophisticated attackers will defeat this, but they can also add a variety of attacks at hardware level

3 comments

nextaccountic

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gorgoiler  1 hour ago

I’d much rather have tamper detection. Encryption is great should the device is stolen but it feels like the wrong tool for defending against evil maids. All I’d want is that any time you open the case or touch the cold external ports (ie unbolted) you have to re-authenticate with a master password. I’m happy to use cabled peripherals to achieve this.

Chaining trust from POST to login feels like trying to make a theoretically perfect diamond and titanium bicycle that never wears down or falls apart when all I need is an automated system to tell me when to replace a part that’s about to fail.

ahepp  5 hours ago

Doing secure boot properly is kind of difficult. There are a bunch of TPM measurement registers for various bits and bobs (kernel, initramfs, cmdline, lots more). Using UKIs simplifies it a lot, but it’s not trivial to do right at the moment.

  • Nextgrid  2 hours ago

    Secure Boot and TPM are separate things. The current Secure Boot policy gets measured by the TPM but that's about it.