integrity: provide a hook to load keys when rootfs is ready

Keys can only be loaded once the rootfs is mounted. Initcalls
are not suitable for that. This patch defines a special hook
to load the x509 public keys onto the IMA keyring, before
attempting to access any file. The keys are required for
verifying the file's signature. The hook is called after the
root filesystem is mounted and before the kernel calls 'init'.

Changes in v3:
* added more explanation to the patch description (Mimi)

Changes in v2:
* Hook renamed as 'integrity_load_keys()' to handle both IMA and EVM
  keys by integrity subsystem.
* Hook patch moved after defining loading functions

Signed-off-by: Dmitry Kasatkin <d.kasatkin@samsung.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
diff --git a/include/linux/integrity.h b/include/linux/integrity.h
index 83222ce..c2d6082 100644
--- a/include/linux/integrity.h
+++ b/include/linux/integrity.h
@@ -24,6 +24,7 @@
 #ifdef CONFIG_INTEGRITY
 extern struct integrity_iint_cache *integrity_inode_get(struct inode *inode);
 extern void integrity_inode_free(struct inode *inode);
+extern void __init integrity_load_keys(void);
 
 #else
 static inline struct integrity_iint_cache *
@@ -36,5 +37,10 @@
 {
 	return;
 }
+
+static inline void integrity_load_keys(void)
+{
+}
 #endif /* CONFIG_INTEGRITY */
+
 #endif /* _LINUX_INTEGRITY_H */