linux-hardening - Re: [PATCH 2/9] security: Move trivial IMA hooks into LSM

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Date:   Fri, 21 Oct 2022 09:53:48 -0500
From:   "Dr. Greg" <greg@...ellic.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Mimi Zohar <zohar@...ux.ibm.com>, Paul Moore <paul@...l-moore.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        Micka?l Sala?n <mic@...ikod.net>, Petr Vorel <pvorel@...e.cz>,
        Borislav Petkov <bp@...e.de>, Takashi Iwai <tiwai@...e.de>,
        Jonathan McDowell <noodles@...com>,
        linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org, KP Singh <kpsingh@...nel.org>,
        Casey Schaufler <casey@...aufler-ca.com>,
        John Johansen <john.johansen@...onical.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH 2/9] security: Move trivial IMA hooks into LSM

On Wed, Oct 19, 2022 at 11:59:40AM -0700, Kees Cook wrote:

Good morning, I hope the week is ending well for everyone.

> On Wed, Oct 19, 2022 at 10:34:48AM -0400, Mimi Zohar wrote:
> >
> > The only thing trivial about making IMA and EVM LSMs is moving
> > them to LSM hooks.  Although static files may be signed and the
> > signatures distributed with the file data through the normal
> > distribution mechanisms (e.g. RPM), other files cannot be signed
> > remotely (e.g.  configuration files).  For these files, both IMA
> > and EVM may be configured to maintain persistent file state stored
> > as security xattrs in the form of security.ima file hashes or
> > security.evm HMACs.  The LSM flexibility of enabling/disabling IMA
> > or EVM on a per boot basis breaks this usage, potentially
> > preventing subsequent boots.

> I'm not suggesting IMA and EVM don't have specific behaviors that
> need to be correctly integrated into the LSM infrastructure. In
> fact, I spent a lot of time designing that infrastructure to be
> flexible enough to deal with these kinds of things. (e.g. plumbing
> "enablement", etc.) As I mentioned, this was more of trying to
> provide a head-start on the conversion. I don't intend to drive this
> -- please take whatever is useful from this example and use it. :)
> I'm happy to help construct any missing infrastructure needed
> (e.g. LSM_ORDER_LAST, etc).

We are 2-3 weeks out from submitting for review and inclusion in the
kernel, a new LSM, and an associated userspace stack, that will have a
high degree of significance with respect to these conversations.

> Kees Cook

Best wishes for a pleasant fall weekend.

As always,

Dr. Greg
The Quixote Project - Flailing at the Travails of Cybersecurity