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

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Message-ID: <20210727025714.3zll7spsmo3opont@kernel.org>
Date:   Tue, 27 Jul 2021 05:57:14 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Ahmad Fatoum <a.fatoum@...gutronix.de>
Cc:     Andreas Rammhold <andreas@...mhold.de>,
        James Bottomley <jejb@...ux.ibm.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        David Howells <dhowells@...hat.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        linux-integrity@...r.kernel.org, keyrings@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        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 Mon, Jul 19, 2021 at 09:10:01AM +0200, Ahmad Fatoum 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.
> 
> 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.

Which of the patches is the bug fix?

/Jarkko