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

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Date:   Wed, 04 Apr 2018 10:43:57 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     David Howells <dhowells@...hat.com>
Cc:     Andy Lutomirski <luto@...nel.org>, Jann Horn <jannh@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Garrett <mjg59@...gle.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

David Howells <dhowells@...hat.com> writes:

> Andy Lutomirski <luto@...nel.org> wrote:
>
>> As far as I can tell, what's really going on here is that there's a
>> significant contingent here that wants to prevent Linux from
>> chainloading something that isn't Linux.
>
> You have completely the wrong end of the stick.  No one has said that or even
> implied that.  You are alleging dishonesty on our part.
>
> What we *have* said is that *if* we want to pass the secure boot state across
> kexec, then we have to make sure that:
>
>  (1) no one tampers with the intermediate kernel between boot and kexec
>      otherwise the secure boot state is effectively invalidated, and
>
>  (2) the image that gets kexec'ed is trusted.
>
> Remember: you cannot know (2) if you don't have (1).
>
> And if someone tampers with the aim of breaking, say, Windows, then someone,
> e.g.  Microsoft, might blacklist the shim.

*Wow*   You just denied this isn't about not booting Windows and a few
lines later said that is your concern.

I was thinking I would have to dig up old archives where I had been told
this before, but you just nicely repeated all of the old arguments so I
don't see the point.

Eric