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Tue, 3 Apr 2018 17:09:06 -0400 X-Google-Smtp-Source: AIpwx49S/1FUA1JVjw9tHS83zaRwC4ZH9hXS++0MKeWO8qrBSYZUZwCHSe4Z02u+x4rMlIdqP/psu5kg/ACz0RSHieg= MIME-Version: 1.0 References: <4136.1522452584@warthog.procyon.org.uk> <186aeb7e-1225-4bb8-3ff5-863a1cde86de@kernel.org> <30459.1522739219@warthog.procyon.org.uk> In-Reply-To: From: Matthew Garrett Date: Tue, 03 Apr 2018 21:08:54 +0000 Message-ID: Subject: Re: [GIT PULL] Kernel lockdown for secure boot To: Linus Torvalds Cc: luto@kernel.org, David Howells , Ard Biesheuvel , jmorris@namei.org, Alan Cox , Greg Kroah-Hartman , Linux Kernel Mailing List , jforbes@redhat.com, linux-man@vger.kernel.org, jlee@suse.com, LSM List , linux-api@vger.kernel.org, Kees Cook , linux-efi Content-Type: text/plain; charset="UTF-8" Sender: linux-efi-owner@vger.kernel.org X-Mailing-List: linux-efi@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Tue, Apr 3, 2018 at 2:01 PM Linus Torvalds wrote: > On Tue, Apr 3, 2018 at 1:54 PM, Matthew Garrett 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.