[PATCH v3] x86/ima: require signed kernel modules

[Mimi Zohar]

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 at linux.ibm.com>
---
 arch/x86/kernel/ima_arch.c | 9 ++++++++-
 include/linux/module.h     | 5 +++++
 kernel/module.c            | 5 +++++
 3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/ima_arch.c b/arch/x86/kernel/ima_arch.c
index e47cd9390ab4..3fb9847f1cad 100644
--- a/arch/x86/kernel/ima_arch.c
+++ b/arch/x86/kernel/ima_arch.c
@@ -64,12 +64,19 @@ static const char * const sb_arch_rules[] = {
 	"appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig",
 #endif /* CONFIG_KEXEC_VERIFY_SIG */
 	"measure func=KEXEC_KERNEL_CHECK",
+#if !IS_ENABLED(CONFIG_MODULE_SIG)
+	"appraise func=MODULE_CHECK appraise_type=imasig",
+#endif
+	"measure func=MODULE_CHECK",
 	NULL
 };
 
 const char * const *arch_get_ima_policy(void)
 {
-	if (IS_ENABLED(CONFIG_IMA_ARCH_POLICY) && arch_ima_get_secureboot())
+	if (IS_ENABLED(CONFIG_IMA_ARCH_POLICY) && arch_ima_get_secureboot()) {
+		if (IS_ENABLED(CONFIG_MODULE_SIG))
+			set_module_sig_enforced();
 		return sb_arch_rules;
+	}
 	return NULL;
 }
diff --git a/include/linux/module.h b/include/linux/module.h
index 8fa38d3e7538..5aaa9359adc8 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -660,6 +660,7 @@ 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... */
 
@@ -780,6 +781,10 @@ 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)
diff --git a/kernel/module.c b/kernel/module.c
index 2ad1b5239910..73cada04bd24 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -286,6 +286,11 @@ bool is_module_sig_enforced(void)
 }
 EXPORT_SYMBOL(is_module_sig_enforced);
 
+void set_module_sig_enforced(void)
+{
+	sig_enforce = true;
+}
+
 /* Block module loading/unloading? */
 int modules_disabled = 0;
 core_param(nomodule, modules_disabled, bint, 0);
-- 
2.7.5