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Date: Wed, 04 Apr 2018 15:29:03 +0200
From: Mike Galbraith <efault@....de>
To: "Theodore Y. Ts'o" <tytso@....edu>,
Matthew Garrett <mjg59@...gle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>, luto@...nel.org,
David Howells <dhowells@...hat.com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>, 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>,
jforbes@...hat.com, linux-man@...r.kernel.org, jlee@...e.com,
LSM List <linux-security-module@...r.kernel.org>,
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 Wed, 2018-04-04 at 08:57 -0400, Theodore Y. Ts'o wrote:
> On Wed, Apr 04, 2018 at 04:30:18AM +0000, Matthew Garrett wrote:
> > What I'm afraid of is this turning into a "security" feature that ends up
> > being circumvented in most scenarios where it's currently deployed - eg,
> > module signatures are mostly worthless in the non-lockdown case because you
> > can just grab the sig_enforce symbol address and then kexec a preamble that
> > flips it back to N regardless of the kernel config.
>
> Whoa. Why doesn't lockdown prevent kexec? Put another away, why
> isn't this a problem for people who are fearful that Linux could be
> used as part of a Windows boot virus in a Secure UEFI context?
>
> If lockdown simply included a requirement for a signed kernel for
> kexec --- and if kernel signing aren't available, to simply not alow
> kexec, wouldn't that take care of this case?
>
> This wouldn't even be all that much of a burden for non-distro users
> with lockdown enabled, since in my experience outside of enterprise
> and data center use cases, kexec isn't used...
Lots of folks use kdump, ergo kexec.
-Mike
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