Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <CACdnJuvW47m3JvEcuEX1bsr+L2Ht9LDn_iCuPbHLOoaohOFW4Q@mail.gmail.com>
 <1551392438.10911.227.camel@linux.ibm.com> <CACdnJuvwnh0PKr5jUTm2h=P5-u-oLgBjvThX+DxcegShXReCdA@mail.gmail.com>
 <1551398720.10911.270.camel@linux.ibm.com>
In-Reply-To: <1551398720.10911.270.camel@linux.ibm.com>
From:   Matthew Garrett <mjg59@google.com>
Date:   Thu, 28 Feb 2019 17:01:59 -0800
Message-ID: <CACdnJutqg26pk5xnK2ii3ia9JabAnBptE3YQ3yLvVT93as666Q@mail.gmail.com>
Subject: Re: [PULL REQUEST] Lock down patches
To:     Mimi Zohar <zohar@linux.ibm.com>
Cc:     jmorris@namei.org,
        LSM List <linux-security-module@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        David Howells <dhowells@redhat.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Feb 28, 2019 at 4:05 PM Mimi Zohar <zohar@linux.ibm.com> wrote:
>
> On Thu, 2019-02-28 at 15:13 -0800, Matthew Garrett wrote:
> > On Thu, Feb 28, 2019 at 2:20 PM Mimi Zohar <zohar@linux.ibm.com> wrote:
> > > Where/when was this latest version of the patches posted?
> >
> > They should have followed this, but git-send-email choked on some
> > reviewed-by: lines so I'm just trying to sort that out.
>
> I'm a little perplexed as to why you would send a pull request, before
> re-posting the patches with the changes for review.

They should be there now. There's no substantive change to the
patches, other than having dropped a few from the series.

> > It's a little more complicated than this. We can't just rely on IMA
> > appraisal - it has to be based on digital signatures, and the existing
> > patch only made that implicit by enabling the secure_boot policy.
>
> Right, which is the reason the IMA architecture specific policy
> requires file signatures. [1][2]

The current patches seem to require ima signatures - shouldn't this
allow ima digests as long as there's an evm signature?

> > I
> > think we do want to integrate these, but there's a few things we need
> > to take into account:
> >
> > 1) An integrated solution can't depend on xattrs, both because of the
> > lagging support for distributing those signatures but also because we
> > need to support filesystems that don't support xattrs
>
> That's not a valid reason for preventing systems that do use IMA for
> verifying the kexec kernel image signature or kernel module signatures
> from enabling "lock down".  This just means that there needs to be
> some coordination between the different signature verification
> methods. [1][2]

I agree, but the current form of the integration makes it impossible
for anyone using an IMA-enabled kernel (but not using IMA) to do
anything unless they have IMA signatures. It's a problem we need to
solve, I just don't think it's a problem we need to solve before
merging the patchset.

> > 2) An integrated solution can't depend on the current secure_boot
> > policy because that requires signed IMA policy updates, but
> > distributions have no way of knowing what IMA policy end users require
>
> Both the "CONFIG_IMA_APPRAISE_REQUIRE_KEXEC_SIGS" and the IMA
> architecture policy rules persist after loading a custom policy.
>  Neither of them require loading or signing a custom policy.

The previous version of the lockdown patchset sets the secure_boot
policy when lockdown is enabled, which does require that any custom
policy be signed.

> > In any case, I do agree that we should aim to make this more
> > reasonable - having orthogonal signing code doesn't benefit anyone.
> > Once there's solid agreement on that we can extend this support.
> >
>
> Having multiple signature verification methods is going to be around
> for a while.  The solution is to coordinate the signature verification
> methods, without requiring both types of signatures. [1][2]

Agree, and once we have a solution to this we should integrate that
with lockdown. I don't think merging this first makes that any harder.
Importantly, this version of the patchset doesn't enable lockdown
automatically unless explicitly configured to do so, which means you
can build a lockdown kernel without interfering with IMA.