linux-kernel - Re: [GIT PULL] Kernel lockdown for secure boot

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Message-ID: <CA+55aFx9u-O81MwSq8zpb+MKaWYjYvtEcFu1NLP1_s63ED6_3Q@mail.gmail.com>
Date:   Tue, 3 Apr 2018 16:39:48 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Matthew Garrett <mjg59@...gle.com>
Cc:     Andrew Lutomirski <luto@...nel.org>,
        David Howells <dhowells@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        James Morris <jmorris@...ei.org>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Justin Forbes <jforbes@...hat.com>,
        linux-man <linux-man@...r.kernel.org>, joeyli <jlee@...e.com>,
        LSM List <linux-security-module@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        linux-efi <linux-efi@...r.kernel.org>
Subject: Re: [GIT PULL] Kernel lockdown for secure boot

On Tue, Apr 3, 2018 at 4:26 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> Magically changing kernel behavior depending on some subtle and often
> unintentional bootup behavior detail is completely idiotic.

Another way of looking at this: if lockdown is a good idea to enable
when you booted using secure boot, then why isn't it a good idea when
you *didn't* boot using secure boot?

That's the flip side of this whole argument.

People who boot without secure boot may be wanting all the same
protections. Maybe you have to disable it when you build your own
kernel, for example. Does that suddenly mean that lockdown is now a
bad idea?

And if it does, explain it. Explain why it's a bad idea to enable
without secure boot, but is a good idea to enable *with* secure boot.

In other words: explain the tie-in.

Because I really don't see it. All I see is illogical blathering that
tries to conflate issues that have nothing to do with each other.

Please explain to me why a distro or a user would want lockdown to be
disabled just because the user didn't use secure boot, but suddenly if
it's booted on another machine, it's not just a good idea, but
mandatory in your world view?

Honestly, if I were a distro maintainer, the *last* thing I'd want is
the kernel to act fundamentally differently in some security context
depending on some random bootup condition.

              Linus