linux-kernel - Re: [PATCH 07/27] kexec_file: Disable at runtime if securelevel has been set

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Date:   Thu, 26 Oct 2017 11:46:45 -0400
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     David Howells <dhowells@...hat.com>, joeyli <jlee@...e.com>
Cc:     linux-security-module@...r.kernel.org, gnomes@...rguk.ukuu.org.uk,
        linux-efi@...r.kernel.org, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, jforbes@...hat.com,
        Matthew Garrett <mjg59@...gle.com>
Subject: Re: [PATCH 07/27] kexec_file: Disable at runtime if securelevel has
 been set

[Cc'ing Matthew Garrett]

On Thu, 2017-10-26 at 16:02 +0100, David Howells wrote:
> joeyli <jlee@...e.com> wrote:
> 
> > +	if (!IS_ENABLED(CONFIG_KEXEC_VERIFY_SIG) &&
> > +	    !is_ima_appraise_enabled() &&
> > +	    kernel_is_locked_down("kexec of unsigned images"))
> 
> This doesn't seem right.  It seems that you can then kexec unsigned images
> into a locked-down kernel if IMA appraise is enabled.

Huh?!  With the "secure_boot" policy enabled on the boot command line,
IMA-appraisal would verify the kexec kernel image, firmware, kernel
modules, and custom IMA policy signatures.  With the "ima: require
secure_boot rules in lockdown mode" patch, the "lockdown" mode would
enable IMA-appraisal's secure_boot policy, without requiring the boot
command line option.  It would also add the secure_boot rules to the
custom policy, so that if the builtin policy is replaced with a custom
policy, the "secure_boot" policy would still be enforced.

Other patches in this patch series need to be updated as well to check
if IMA-appraisal is enabled.

Mimi