integrity: Enforce digitalSignature usage in the ima and evm keyrings

After being vouched for by a system keyring, only allow keys into the .ima
and .evm keyrings that have the digitalSignature usage field set.

Link: https://lore.kernel.org/all/41dffdaeb7eb7840f7e38bc691fbda836635c9f9.camel@linux.ibm.comSuggested-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
Acked-and-tested-by: Mimi Zohar <zohar@linux.ibm.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

security/integrity/digsig.c

@@ -34,9 +34,9 @@ static const char * const keyring_name[INTEGRITY_KEYRING_MAX] = {
 };
 
 #ifdef CONFIG_IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY
-#define restrict_link_to_ima restrict_link_by_builtin_and_secondary_trusted
+#define restrict_link_to_ima restrict_link_by_digsig_builtin_and_secondary
 #else
-#define restrict_link_to_ima restrict_link_by_builtin_trusted
+#define restrict_link_to_ima restrict_link_by_digsig_builtin
 #endif
 
 static struct key *integrity_keyring_from_id(const unsigned int id)

security/integrity/evm/Kconfig

@@ -64,7 +64,8 @@ config EVM_LOAD_X509
 
 	   This option enables X509 certificate loading from the kernel
 	   onto the '.evm' trusted keyring.  A public key can be used to
-	   verify EVM integrity starting from the 'init' process.
+	   verify EVM integrity starting from the 'init' process. The
+	   key must have digitalSignature usage set.
 
 config EVM_X509_PATH
 	string "EVM X509 certificate path"

security/integrity/ima/Kconfig

@@ -270,7 +270,8 @@ config IMA_KEYRINGS_PERMIT_SIGNED_BY_BUILTIN_OR_SECONDARY
 	help
 	  Keys may be added to the IMA or IMA blacklist keyrings, if the
 	  key is validly signed by a CA cert in the system built-in or
-	  secondary trusted keyrings.
+	  secondary trusted keyrings. The key must also have the
+	  digitalSignature usage set.
 
 	  Intermediate keys between those the kernel has compiled in and the
 	  IMA keys to be added may be added to the system secondary keyring,