[GIT PULL] Kernel lockdown for secure boot

[Matthew Garrett]

On Tue, Apr 3, 2018 at 2:01 PM Linus Torvalds
<torvalds at linux-foundation.org>
wrote:

> On Tue, Apr 3, 2018 at 1:54 PM, Matthew Garrett <mjg59 at google.com> wrote:
> >
> >> .. maybe you don't *want* secure boot, but it's been pushed in your
> >> face by people with an agenda?
> >
> > Then turn it off, or build a self-signed kernel that doesn't do this?

> Umm. So you asked a question, and then when you got an answer you said
> "don't do that then".

> The fact is, some hardware pushes secure boot pretty hard. That has
> *nothing* to do with some "lockdown" mode.

Secure Boot ensures that the firmware will only load signed bootloaders. If
a signed bootloader loads a kernel that's effectively an unsigned
bootloader, there's no point in using Secure Boot - you should just turn it
off instead, because it's not giving you any meaningful security. Andy's
example gives a scenario where by constraining your *userland* sufficiently
you can get close to having the same guarantees, but that involves you
having a read-only filesystem and takes you even further away from having a
general purpose computer.

If you don't want Secure Boot, turn it off. If you want Secure Boot, use a
kernel that behaves in a way that actually increases your security.
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