linux-kernel - Re: [PATCH] integrity: powerpc: Do not select CA_MACHINE

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Message-ID: <f5759a6275ca1e978f33fb7bad53ee68a79d3609.camel@linux.ibm.com>
Date:   Tue, 12 Sep 2023 15:56:52 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>,
        Michal Suchánek <msuchanek@...e.de>,
        Nayna <nayna@...ux.vnet.ibm.com>
Cc:     linux-integrity@...r.kernel.org,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        Paul Moore <paul@...l-moore.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, joeyli <jlee@...e.com>,
        Eric Snowberg <eric.snowberg@...cle.com>,
        Nayna Jain <nayna@...ux.ibm.com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH] integrity: powerpc: Do not select CA_MACHINE_KEYRING

On Tue, 2023-09-12 at 22:32 +0300, Jarkko Sakkinen wrote:
> On Tue Sep 12, 2023 at 10:22 PM EEST, Mimi Zohar wrote:
> > On Tue, 2023-09-12 at 12:49 +0300, Jarkko Sakkinen wrote:
> > > On Tue Sep 12, 2023 at 10:41 AM EEST, Michal Suchánek wrote:
> > > > On Mon, Sep 11, 2023 at 11:39:38PM -0400, Nayna wrote:
> > > > > 
> > > > > On 9/7/23 13:32, Michal Suchánek wrote:
> > > > > > Adding more CC's from the original patch, looks like get_maintainers is
> > > > > > not that great for this file.
> > > > > > 
> > > > > > On Thu, Sep 07, 2023 at 06:52:19PM +0200, Michal Suchanek wrote:
> > > > > > > No other platform needs CA_MACHINE_KEYRING, either.
> > > > > > > 
> > > > > > > This is policy that should be decided by the administrator, not Kconfig
> > > > > > > dependencies.
> > > > > 
> > > > > We certainly agree that flexibility is important. However, in this case,
> > > > > this also implies that we are expecting system admins to be security
> > > > > experts. As per our understanding, CA based infrastructure(PKI) is the
> > > > > standard to be followed and not the policy decision. And we can only speak
> > > > > for Power.
> > > > > 
> > > > > INTEGRITY_CA_MACHINE_KEYRING ensures that we always have CA signed leaf
> > > > > certs.
> > > >
> > > > And that's the problem.
> > > >
> > > > From a distribution point of view there are two types of leaf certs:
> > > >
> > > >  - leaf certs signed by the distribution CA which need not be imported
> > > >    because the distribution CA cert is enrolled one way or another
> > > >  - user generated ad-hoc certificates that are not signed in any way,
> > > >    and enrolled by the user
> > > >
> > > > The latter are vouched for by the user by enrolling the certificate, and
> > > > confirming that they really want to trust this certificate. Enrolling
> > > > user certificates is vital for usability or secure boot. Adding extra
> > > > step of creating a CA certificate stored on the same system only
> > > > complicates things with no added benefit.
> > > 
> > > This all comes down to the generic fact that kernel should not
> > > proactively define what it *expects* sysadmins.
> > > 
> > > CA based infrastructure like anything is a policy decision not
> > > a decision to be enforced by kernel.
> >
> > Secure boot requires a signature chain of trust.  IMA extends the
> > secure and trusted boot concepts to the kernel. Missing from that
> > signature chain of trust is the ability of allowing the end
> > machine/system owner to load other certificates without recompiling the
> > kernel. The introduction of the machine keyring was to address this.
> >
> > I'm not questioning the end user's intent on loading local or third
> > party keys via the normal mechanisms. If the existing mechanism(s) for
> > loading local or third party keys were full-proof, then loading a
> > single certificate, self-signed or not, would be fine. However, that
> > isn't the reality.  The security of the two-stage approach is simply
> > not equivalent to loading a single certificate.  Documentation could
> > help the end user/system owner to safely create (and manage) separate
> > certificate signing and code signing certs.
> >
> > Unlike UEFI based systems, PowerVM defines two variables trustedcadb
> > and moduledb, for storing certificate signing and code signing
> > certificates respectively.  First the certs on the trustedcadb are
> > loaded and then the ones on moduledb are loaded.
> 
> There's pragmatic reasons to make things more open than they should be
> in production. As a hardware example I still possess Raspberry Pi 3B for
> test workloads because it has a broken TZ implementation. The world is
> really bigger than production workloads.
> 
> It would be better to document what you said rather than enforce the
> right choice IMHO (e.g. extend Kconfig documentation).

PowerVM LPARs are more about production workloads than a Raspberry Pi. 
:)

-- 
thanks,

Mimi