Re: [PATCH v2] KEYS: trusted: fix use as module when CONFIG_TCG_TPM=m

From: Jarkko Sakkinen <jarkko@kernel.org>
To: Ahmad Fatoum <a.fatoum@pengutronix.de>
Cc: James Morris <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	James Bottomley <jejb@linux.ibm.com>,
	Mimi Zohar <zohar@linux.ibm.com>,
	Sumit Garg <sumit.garg@linaro.org>,
	David Howells <dhowells@redhat.com>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	"David S. Miller" <davem@davemloft.net>,
	kernel@pengutronix.de, Andreas Rammhold <andreas@rammhold.de>,
	David Gstir <david@sigma-star.at>,
	Richard Weinberger <richard@nod.at>,
	keyrings@vger.kernel.org, linux-crypto@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	linux-integrity@vger.kernel.org
Subject: Re: [PATCH v2] KEYS: trusted: fix use as module when CONFIG_TCG_TPM=m
Date: Tue, 27 Jul 2021 06:04:33 +0300	[thread overview]
Message-ID: <20210727030433.3dwod2elwtdkhwsc@kernel.org> (raw)
In-Reply-To: <20210721160258.7024-1-a.fatoum@pengutronix.de>

On Wed, Jul 21, 2021 at 06:02:59PM +0200, Ahmad Fatoum wrote:
> Since commit 5d0682be3189 ("KEYS: trusted: Add generic trusted keys
> framework"), trusted.ko built with CONFIG_TCG_TPM=CONFIG_TRUSTED_KEYS=m
> will not register the TPM trusted key type at runtime.
> 
> This is because, after that rework, CONFIG_DEPENDENCY of the TPM
> and TEE backends were checked with #ifdef, but that's only true
> when they're built-in.
> 
> Fix this by introducing two new boolean Kconfig symbols:
> TRUSTED_KEYS_TPM and TRUSTED_KEYS_TEE with the appropriate
> dependencies and use them to check which backends are available.
> 
> This also has a positive effect on user experience:
> 
>  - It's now possible to use TEE trusted keys without CONFIG_TCG_TPM
>  - It's now possible to enable CONFIG_TCG_TPM, but exclude TPM from
>    available trust sources
>  - TEE=m && TRUSTED_KEYS=y no longer leads to TEE support
>    being silently dropped
> 
> Any code depending on the TPM trusted key backend or symbols exported
> by it will now need to explicitly state that it
> 
>   depends on TRUSTED_KEYS && TRUSTED_KEYS_TPM
> 
> The latter to ensure the dependency is built and the former to ensure
> it's reachable for module builds. This currently only affects
> CONFIG_ASYMMETRIC_TPM_KEY_SUBTYPE, so it's fixed up here as well.
> 
> Reported-by: Andreas Rammhold <andreas@rammhold.de>
> Fixes: 5d0682be3189 ("KEYS: trusted: Add generic trusted keys framework")
> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>

Is it absolutely need to do all this *just* to fix the bug?

For a pure bug fix the most essential thing is to be able the backport
it to stable kernels.

I don't really care at all about extra niceties ("it's now possible
stuff).

This looks like a bug fix and improvements bundle into a single patch.

/Jarkko