linux-kernel - [PATCH] x86/ima: require signed kernel modules

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Message-Id: <1548962339-10681-2-git-send-email-zohar@linux.ibm.com>
Date:   Thu, 31 Jan 2019 14:18:59 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     linux-integrity@...r.kernel.org
Cc:     linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jessica Yu <jeyu@...nel.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        David Howells <dhowells@...hat.com>,
        Seth Forshee <seth.forshee@...onical.com>,
        Justin Forbes <jforbes@...hat.com>,
        Matthew Garrett <mjg59@...gle.com>,
        Mimi Zohar <zohar@...ux.ibm.com>
Subject: [PATCH] x86/ima: require signed kernel modules

Require signed kernel modules on systems with secure boot mode enabled.

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.

This patch defines a function named set_module_sig_required() and renames
is_module_sig_enforced() to is_module_sig_enforced_or_required().  The
call to set_module_sig_required() is dependent on CONFIG_IMA_ARCH_POLICY
being enabled.

Signed-off-by: Mimi Zohar <zohar@...ux.ibm.com>
---
 arch/x86/kernel/ima_arch.c        |  9 ++++++++-
 include/linux/module.h            |  7 ++++++-
 kernel/module.c                   | 15 +++++++++++----
 security/integrity/ima/ima_main.c |  2 +-
 4 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/ima_arch.c b/arch/x86/kernel/ima_arch.c
index e47cd9390ab4..96a023238a83 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_required();
 		return sb_arch_rules;
+	}
 	return NULL;
 }
diff --git a/include/linux/module.h b/include/linux/module.h
index 8fa38d3e7538..af51c8ec755f 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -659,7 +659,8 @@ static inline bool is_livepatch_module(struct module *mod)
 }
 #endif /* CONFIG_LIVEPATCH */
 
-bool is_module_sig_enforced(void);
+bool is_module_sig_enforced_or_required(void);
+void set_module_sig_required(void);
 
 #else /* !CONFIG_MODULES... */
 
@@ -780,6 +781,10 @@ static inline bool is_module_sig_enforced(void)
 	return false;
 }
 
+static inline void set_module_sig_required(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..70a9709d19eb 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -275,16 +275,23 @@ static void module_assert_mutex_or_preempt(void)
 
 static bool sig_enforce = IS_ENABLED(CONFIG_MODULE_SIG_FORCE);
 module_param(sig_enforce, bool_enable_only, 0644);
+static bool sig_required;
 
 /*
  * Export sig_enforce kernel cmdline parameter to allow other subsystems rely
  * on that instead of directly to CONFIG_MODULE_SIG_FORCE config.
  */
-bool is_module_sig_enforced(void)
+bool is_module_sig_enforced_or_required(void)
 {
-	return sig_enforce;
+	return sig_enforce || sig_required;
 }
-EXPORT_SYMBOL(is_module_sig_enforced);
+EXPORT_SYMBOL(is_module_sig_enforced_or_required);
+
+void set_module_sig_required(void)
+{
+	sig_required = true;
+}
+EXPORT_SYMBOL(set_module_sig_required);
 
 /* Block module loading/unloading? */
 int modules_disabled = 0;
@@ -2789,7 +2796,7 @@ static int module_sig_check(struct load_info *info, int flags)
 	}
 
 	/* Not having a signature is only an error if we're strict. */
-	if (err == -ENOKEY && !is_module_sig_enforced())
+	if (err == -ENOKEY && !is_module_sig_enforced_or_required())
 		err = 0;
 
 	return err;
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 357edd140c09..bbaf87f688be 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -563,7 +563,7 @@ int ima_load_data(enum kernel_load_data_id id)
 		}
 		break;
 	case LOADING_MODULE:
-		sig_enforce = is_module_sig_enforced();
+		sig_enforce = is_module_sig_enforced_or_required();
 
 		if (ima_enforce && (!sig_enforce
 				    && (ima_appraise & IMA_APPRAISE_MODULES))) {
-- 
2.7.5