linux-kernel - Re: [PATCH] KEYS: trusted: Fix trusted key backends when building as module

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Message-ID: <20210719091335.vwfebcpkf4pag3wm@wrt>
Date:   Mon, 19 Jul 2021 11:13:35 +0200
From:   andreas@...mhold.de
To:     Sumit Garg <sumit.garg@...aro.org>,
        Ahmad Fatoum <a.fatoum@...gutronix.de>
Cc:     James Bottomley <jejb@...ux.ibm.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        David Howells <dhowells@...hat.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        linux-integrity <linux-integrity@...r.kernel.org>,
        "open list:ASYMMETRIC KEYS" <keyrings@...r.kernel.org>,
        "open list:SECURITY SUBSYSTEM" 
        <linux-security-module@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>
Subject: Re: [PATCH] KEYS: trusted: Fix trusted key backends when building as
 module

On 13:36 19.07.21, Sumit Garg wrote:
> On Mon, 19 Jul 2021 at 12:40, Ahmad Fatoum <a.fatoum@...gutronix.de> wrote:
> >
> > Hello Andreas,
> >
> > On 16.07.21 10:17, Andreas Rammhold wrote:
> > > Before this commit the kernel could end up with no trusted key sources
> > > even thought both of the currently supported backends (tpm & tee) were
> > > compoiled as modules. This manifested in the trusted key type not being
> > > registered at all.
> >
> > I assume (TPM) trusted key module use worked before the TEE rework? If so,
> >
> > an appropriate Fixes: Tag would then be in order.
> >
> > > When checking if a CONFIG_… preprocessor variable is defined we only
> > > test for the builtin (=y) case and not the module (=m) case. By using
> > > the IS_ENABLE(…) macro we to test for both cases.
> >
> > It looks to me like you could now provoke a link error if TEE is a module
> > and built-in trusted key core tries to link against trusted_key_tee_ops.
> >
> 
> That's true.
> 
> > One solution for that IS_REACHABLE(). Another is to address the root cause,
> > which is the inflexible trusted keys Kconfig description:
> >
> > - Trusted keys despite TEE support can still only be built when TCG_TPM is enabled
> > - There is no support to have TEE or TPM enabled without using those for
> >   enabled trusted keys as well
> > - As you noticed, module build of the backend has issues
> >
> > I addressed these three issues in a patch[1], a month ago, but have yet to
> > receive feedback.
> 
> That's an oversight on my part since this patch was part of the new
> CAAM trust source patch-set. Although I do admit that it was on my
> TODO list. So I have provided some feedback on that patch. Can you
> post the next version as an independent fix patch?

Thank you both for the feedback. In light of thes feedback and the
patchset that Ahmad posted I'll not address the issue and not send a v2
of this.

I'll try to squeeze in some time to test the other patch and provide
feedback.

Andi