Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <CA+55aFzYbpRAdma0PvqE+9ygySuKzNKByqOzzMufBoovXVnfPw@mail.gmail.com>
 <CACdnJuv-VpdhjEe1cMysdHb6Oy67jQqg-_TVHbUrOfH9GmCVvg@mail.gmail.com>
 <CA+55aFwvuoSHhKnn82VnDndZ6oXMJgwHF604gZ=h3ehHyC600A@mail.gmail.com>
 <CA+55aFzJ2sQR13T+20MKEJ5co-f3Ev8rRxQkRCWVaeDSUU3yhQ@mail.gmail.com>
 <CACdnJuti5Riqoi1sesqPALYHq9LT87o4MFj-0Y5BZqqzJ5579g@mail.gmail.com>
 <CA+55aFwhi=gz3HLoGST9--n1_kLJNP6jsf8GSesSFxTDCdPdtQ@mail.gmail.com>
 <CACdnJuuek-sS3esmomNOkjBMV_6VPL2NFCzRd+UGxbZrMe=4nw@mail.gmail.com>
 <CA+55aFxgrh5eeG9MRSEsJtyL5yTe0TehZ=BS2josGJaLxoMMBQ@mail.gmail.com>
 <CACdnJutuBaE3RaDx0KM5vDF9Sinrp=3tG9csrS-H3eU-J7-Utw@mail.gmail.com>
 <24353.1522848817@warthog.procyon.org.uk> <20180404135251.GD16242@thunk.org>
 <CACdnJuuGRRUt-a3i89o906ka3RDOhs+_7tz_G8LTG8Jc0DXAyQ@mail.gmail.com> <CALCETrXwp1faWnqRJ5iLeo6bOOrRS_-L74_xnRAN1Md1YZW8Tg@mail.gmail.com>
In-Reply-To: <CALCETrXwp1faWnqRJ5iLeo6bOOrRS_-L74_xnRAN1Md1YZW8Tg@mail.gmail.com>
From:   Matthew Garrett <mjg59@google.com>
Date:   Wed, 04 Apr 2018 16:42:20 +0000
Message-ID: <CACdnJutctrxMUKfXxOXv6Z6mrjeZh8xFmg0Yhid56G2YCWGHVA@mail.gmail.com>
Subject: Re: [GIT PULL] Kernel lockdown for secure boot
To:     luto@kernel.org
Cc:     tytso@mit.edu, David Howells <dhowells@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>, jmorris@namei.org,
        Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        jforbes@redhat.com, linux-man@vger.kernel.org, jlee@suse.com,
        LSM List <linux-security-module@vger.kernel.org>,
        linux-api@vger.kernel.org, Kees Cook <keescook@chromium.org>,
        linux-efi <linux-efi@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, Apr 4, 2018 at 9:39 AM Andy Lutomirski <luto@kernel.org> wrote:
> On Wed, Apr 4, 2018 at 9:22 AM, Matthew Garrett <mjg59@google.com> wrote:
> > If you don't have secure boot then an attacker with root can modify your
> > bootloader or kernel, and on next boot lockdown can be silently
disabled.

> This has been rebutted over and over and over.  Secure boot is not the
> only verified boot mechanism in the world.  Other, better, much more
> auditable, and much simpler mechanisms have been around for a long,
> long time.

Right and if you *know* that you're in that situation then you either turn
it on in bootparams from the verified bootloader (which we can't do in UEFI
because the *firmware* can be the bootloader thanks to the EFI boot stub)
or you enable it from userland later (I can't remember if this version of
the patchset provides that functionality, but a previous one did).

> > Which is why Shim allows you to disable validation if you prove physical
> > user presence.

> And that's a giant hack.  The actual feature should be that a user
> proves physical presence and thus disables lockdown *without*
> disabling verification.

That's a completely reasonable feature request.