[PATCH RESEND] KEYS: trusted: Fix trusted key backends when building as module

[andreas@rammhold.de]

From: Andreas Rammhold <andreas@rammhold.de>

Before this commit the kernel could end up with no trusted key sources
even though both of the currently supported backends (TPM and TEE) were
compiled as modules. This manifested in the trusted key type not being
registered at all.

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_REACHABLE() macro we do test for both cases.

Fixes: 5d0682be3189 ("KEYS: trusted: Add generic trusted keys framework")
Signed-off-by: Andreas Rammhold <andreas@rammhold.de>
---

This is a resend becuase of this unfortunate timeline:
  - 2021-05-09: Regression hits mainline with v5.13-rc1
  - 2021-07-16: Issue reported. v1 of this patch sent out
  - 2021-07-21: Ahmad sends out alternative patch to fix issue
  - 2021-07-27: Jarkko (Maintainer) NACKs Ahmad's patch because of scope
  - 2021-07-29: v2 with fixes sent out
  - 2021-07-29: Jarkko gives his Reviewed-by and requests one more v3
  - 2021-07-31: v3 sent out
  - 2021-09-13: Pinged, no feedback
  - 2021-09-27: Pinged, Mimi (Maintainer) comments due to to misunderstanding.
                Question about why this is not merged ignored
  - 2021-10-11: Pinged, no feedback

v3:
* Fixed patch formatting

v2:
* Fixed commit message
* Switched from IS_DEFINED() to IS_REACHABLE()


 security/keys/trusted-keys/trusted_core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/security/keys/trusted-keys/trusted_core.c b/security/keys/trusted-keys/trusted_core.c
index d5c891d8d3534..5b35f1b876441 100644
--- a/security/keys/trusted-keys/trusted_core.c
+++ b/security/keys/trusted-keys/trusted_core.c
@@ -27,10 +27,10 @@ module_param_named(source, trusted_key_source, charp, 0);
 MODULE_PARM_DESC(source, "Select trusted keys source (tpm or tee)");
 
 static const struct trusted_key_source trusted_key_sources[] = {
-#if defined(CONFIG_TCG_TPM)
+#if IS_REACHABLE(CONFIG_TCG_TPM)
 	{ "tpm", &trusted_key_tpm_ops },
 #endif
-#if defined(CONFIG_TEE)
+#if IS_REACHABLE(CONFIG_TEE)
 	{ "tee", &trusted_key_tee_ops },
 #endif
 };
-- 
2.33.0