linux-kernel - Re: [PATCH] x86/ima: require signed kernel modules

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Date:   Fri, 8 Feb 2019 13:21:27 -0600
From:   Seth Forshee <seth.forshee@...onical.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jessica Yu <jeyu@...nel.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        David Howells <dhowells@...hat.com>,
        Justin Forbes <jforbes@...hat.com>,
        Matthew Garrett <mjg59@...gle.com>
Subject: Re: [PATCH] x86/ima: require signed kernel modules

On Tue, Feb 05, 2019 at 01:52:21PM -0500, Mimi Zohar wrote:
> On Tue, 2019-02-05 at 12:32 -0600, Seth Forshee wrote:
> > On Tue, Feb 05, 2019 at 11:47:24AM -0500, Mimi Zohar wrote:
> > > Hi Seth,
> > > 
> > > On Tue, 2019-02-05 at 09:18 -0600, Seth Forshee wrote:
> > > > On Thu, Jan 31, 2019 at 02:18:59PM -0500, Mimi Zohar wrote:
> > > > > Require signed kernel modules on systems with secure boot mode enabled.
> > > > > 
> > > > > To coordinate between appended kernel module signatures and IMA
> > > > > signatures, only define an IMA MODULE_CHECK policy rule if
> > > > > CONFIG_MODULE_SIG is not enabled.
> > > > > 
> > > > > This patch defines a function named set_module_sig_required() and renames
> > > > > is_module_sig_enforced() to is_module_sig_enforced_or_required().  The
> > > > > call to set_module_sig_required() is dependent on CONFIG_IMA_ARCH_POLICY
> > > > > being enabled.
> > > > > 
> > > > > Signed-off-by: Mimi Zohar <zohar@...ux.ibm.com>
> > > > 
> > > > With respect to interactions with the kernel lockdown patches, this
> > > > looks better than the patches I saw previously. I don't feel like I know
> > > > enough about what's going on with IMA to ack the patch, but I feel
> > > > confident that it's at least not going to break signature enforcement
> > > > for us.
> > > 
> > > Thank you for testing!  Could this be translated into a "tested-by"
> > > "(for w/lockdown patches)"?
> > 
> > Yeah, that's fine. To be clear about what I tested, I've confirmed that
> > it doesn't interfere with requiring signed modules under lockdown with
> > CONFIG_IMA_ARCH_POLICY=n and IMA appraisal enabled.
> > 
> > Tested-by: Seth Forshee <seth.forshee@...onical.com>
> 
> Oh!  You've disabled the coordination of the two signature
> verification methods.  Any chance you could test with
> "CONFIG_IMA_ARCH_POLICY" enabled?

Ok, I've tested this now and it also seems to be working. However it
does seem redundant to have CONFIG_IMA_ARCH_POLICY alongside lockdown,
as it doesn't enforce anything not already being enforced by lockdown.

Seth