IMA: fix measuring asymmetric keys Kconfig

As a result of the asymmetric public keys subtype Kconfig option being
defined as tristate, with the existing IMA Makefile, ima_asymmetric_keys.c
could be built as a kernel module.  To prevent this from happening, this
patch defines and uses an intermediate Kconfig boolean option named
IMA_MEASURE_ASYMMETRIC_KEYS.
Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Suggested-by: James.Bottomley <James.Bottomley@HansenPartnership.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Reported-by: kbuild test robot <lkp@intel.com> # ima_asymmetric_keys.c
is built as a kernel module.
Fixes: 88e70da1 ("IMA: Define an IMA hook to measure keys")
Fixes: cb1aa382 ("KEYS: Call the IMA hook to measure keys")
[zohar@linux.ibm.com: updated patch description]
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

include/linux/ima.h

@@ -101,7 +101,7 @@ static inline void ima_add_kexec_buffer(struct kimage *image)
 {}
 #endif
 
-#if defined(CONFIG_IMA) && defined(CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE)
+#ifdef CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS
 extern void ima_post_key_create_or_update(struct key *keyring,
 					  struct key *key,
 					  const void *payload, size_t plen,
@@ -113,7 +113,7 @@ static inline void ima_post_key_create_or_update(struct key *keyring,
 						 size_t plen,
 						 unsigned long flags,
 						 bool create) {}
-#endif  /* CONFIG_IMA && CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE */
+#endif  /* CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS */
 
 #ifdef CONFIG_IMA_APPRAISE
 extern bool is_ima_appraise_enabled(void);

security/integrity/ima/Kconfig

@@ -310,3 +310,9 @@ config IMA_APPRAISE_SIGNED_INIT
 	default n
 	help
 	   This option requires user-space init to be signed.
+
+config IMA_MEASURE_ASYMMETRIC_KEYS
+	bool
+	depends on IMA
+	depends on ASYMMETRIC_PUBLIC_KEY_SUBTYPE=y
+	default y

security/integrity/ima/Makefile

@@ -12,4 +12,4 @@ ima-$(CONFIG_IMA_APPRAISE) += ima_appraise.o
 ima-$(CONFIG_IMA_APPRAISE_MODSIG) += ima_modsig.o
 ima-$(CONFIG_HAVE_IMA_KEXEC) += ima_kexec.o
 obj-$(CONFIG_IMA_BLACKLIST_KEYRING) += ima_mok.o
-obj-$(CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE) += ima_asymmetric_keys.o
+obj-$(CONFIG_IMA_MEASURE_ASYMMETRIC_KEYS) += ima_asymmetric_keys.o