x86/ima: require signed kernel modules

Have the IMA architecture specific policy require signed kernel modules
on systems with secure boot mode enabled; and coordinate the different
signature verification methods, so only one signature is required.

Requiring appended kernel module signatures may be configured, enabled
on the boot command line, or with this patch enabled in secure boot
mode.  This patch defines set_module_sig_enforced().

To coordinate between appended kernel module signatures and IMA
signatures, only define an IMA MODULE_CHECK policy rule if
CONFIG_MODULE_SIG is not enabled.  A custom IMA policy may still define
and require an IMA signature.

Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Acked-by: Jessica Yu <jeyu@kernel.org>

include/linux/module.h

@@ -676,6 +676,7 @@ static inline bool is_livepatch_module(struct module *mod)
 #endif /* CONFIG_LIVEPATCH */
 
 bool is_module_sig_enforced(void);
+void set_module_sig_enforced(void);
 
 #else /* !CONFIG_MODULES... */
 
@@ -796,6 +797,10 @@ static inline bool is_module_sig_enforced(void)
 	return false;
 }
 
+static inline void set_module_sig_enforced(void)
+{
+}
+
 /* Dereference module function descriptor */
 static inline
 void *dereference_module_function_descriptor(struct module *mod, void *ptr)