linux-kernel - Re: [PATCH 03/27] Enforce module signatures if the kernel is locked down

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Date:   Thu, 02 Nov 2017 17:41:21 -0400
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-security-module@...r.kernel.org, gnomes@...rguk.ukuu.org.uk,
        linux-efi@...r.kernel.org, matthew.garrett@...ula.com,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        jforbes@...hat.com
Subject: Re: [PATCH 03/27] Enforce module signatures if the kernel is locked
 down

On Thu, 2017-11-02 at 21:30 +0000, David Howells wrote:
> Mimi Zohar <zohar@...ux.vnet.ibm.com> wrote:
> 
> > By this point, IMA-appraisal has already verified the kernel module
> > signature back in kernel_read_file_from_fd(), if it was required.
> >  Having a key with which to verify the appended signature or requiring
> > an appended signature, should not be required as well.
> 
> I guess I don't need to put in any support for IMA here, then, and you've
> taken care of it in your patchset such that it won't actually go into
> module_sig_check() in that case (or will at least return immediately).

Right, it would never get here if the IMA signature verification
fails.  If sig_enforce is not enabled, then it will also work.  So the
only case is if sig_enforced is enabled and there is no key.

eg.
         else if (can_do_ima_check && is_ima_appraise_enabled())
                err = 0;

Mimi