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Subject: Re: [GIT PULL] Kernel lockdown for secure boot
From:   Mike Galbraith <efault@gmx.de>
To:     "Theodore Y. Ts'o" <tytso@mit.edu>,
        Matthew Garrett <mjg59@google.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>, luto@kernel.org,
        David Howells <dhowells@redhat.com>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>, jmorris@namei.org,
        Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
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        linux-api@vger.kernel.org, Kees Cook <keescook@chromium.org>,
        linux-efi <linux-efi@vger.kernel.org>
Date:   Wed, 04 Apr 2018 15:29:03 +0200
In-Reply-To: <20180404125743.GB16242@thunk.org>
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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