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:

quoted

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.

quoted

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