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Subject: Re: [PATCH V31 07/25] kexec_file: Restrict at runtime if the kernel
 is locked down
From:   Mimi Zohar <zohar@linux.ibm.com>
To:     Matthew Garrett <mjg59@google.com>, Dave Young <dyoung@redhat.com>
Cc:     James Morris <jmorris@namei.org>, Jiri Bohac <jbohac@suse.cz>,
        Linux API <linux-api@vger.kernel.org>,
        kexec@lists.infradead.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        David Howells <dhowells@redhat.com>,
        LSM List <linux-security-module@vger.kernel.org>,
        Andy Lutomirski <luto@kernel.org>
Date:   Mon, 24 Jun 2019 17:27:37 -0400
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Hi Matthew,

On Mon, 2019-06-24 at 14:06 -0700, Matthew Garrett wrote:
> On Sun, Jun 23, 2019 at 6:52 PM Dave Young <dyoung@redhat.com> wrote:
> >
> > On 06/21/19 at 01:18pm, Matthew Garrett wrote:
> > > I don't think so - we want it to be possible to load images if they
> > > have a valid signature.
> >
> > I know it works like this way because of the previous patch.  But from
> > the patch log "When KEXEC_SIG is not enabled, kernel should not load
> > images", it is simple to check it early for !IS_ENABLED(CONFIG_KEXEC_SIG) &&
> > kernel_is_locked_down(reason, LOCKDOWN_INTEGRITY)  instead of depending
> > on the late code to verify signature.  In that way, easier to
> > understand the logic, no?
> 
> But that combination doesn't enforce signature validation? We can't
> depend on !IS_ENABLED(CONFIG_KEXEC_SIG_FORCE) because then it'll
> enforce signature validation even if lockdown is disabled.

I agree with Dave.  There should be a stub lockdown function to
prevent enforcing lockdown when it isn't enabled.

Mimi