LSM: LoadPin for kernel file loading restrictions

This LSM enforces that kernel-loaded files (modules, firmware, etc)
must all come from the same filesystem, with the expectation that
such a filesystem is backed by a read-only device such as dm-verity
or CDROM. This allows systems that have a verified and/or unchangeable
filesystem to enforce module and firmware loading restrictions without
needing to sign the files individually.

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>

include/linux/lsm_hooks.h

@@ -1892,5 +1892,10 @@ extern void __init yama_add_hooks(void);
 #else
 static inline void __init yama_add_hooks(void) { }
 #endif
+#ifdef CONFIG_SECURITY_LOADPIN
+void __init loadpin_add_hooks(void);
+#else
+static inline void loadpin_add_hooks(void) { };
+#endif
 
 #endif /* ! __LINUX_LSM_HOOKS_H */