ima: add support for arch specific policies

Builtin IMA policies can be enabled on the boot command line, and replaced
with a custom policy, normally during early boot in the initramfs. Build
time IMA policy rules were recently added. These rules are automatically
enabled on boot and persist after loading a custom policy.

There is a need for yet another type of policy, an architecture specific
policy, which is derived at runtime during kernel boot, based on the
runtime secure boot flags.  Like the build time policy rules, these rules
persist after loading a custom policy.

This patch adds support for loading an architecture specific IMA policy.

Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
Co-Developed-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

include/linux/ima.h

@@ -39,6 +39,11 @@ static inline bool arch_ima_get_secureboot(void)
 }
 #endif
 
+static inline const char * const *arch_get_ima_policy(void)
+{
+	return NULL;
+}
+
 #else
 static inline int ima_bprm_check(struct linux_binprm *bprm)
 {

security/integrity/ima/ima_policy.c

@@ -20,6 +20,7 @@
 #include <linux/rculist.h>
 #include <linux/genhd.h>
 #include <linux/seq_file.h>
+#include <linux/ima.h>
 
 #include "ima.h"
 
@@ -195,6 +196,9 @@ static struct ima_rule_entry secure_boot_rules[] __ro_after_init = {
 	 .flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
 };
 
+/* An array of architecture specific rules */
+struct ima_rule_entry *arch_policy_entry __ro_after_init;
+
 static LIST_HEAD(ima_default_rules);
 static LIST_HEAD(ima_policy_rules);
 static LIST_HEAD(ima_temp_rules);
@@ -501,6 +505,49 @@ static void add_rules(struct ima_rule_entry *entries, int count,
 	}
 }
 
+static int ima_parse_rule(char *rule, struct ima_rule_entry *entry);
+
+static int __init ima_init_arch_policy(void)
+{
+	const char * const *arch_rules;
+	const char * const *rules;
+	int arch_entries = 0;
+	int i = 0;
+
+	arch_rules = arch_get_ima_policy();
+	if (!arch_rules)
+		return arch_entries;
+
+	/* Get number of rules */
+	for (rules = arch_rules; *rules != NULL; rules++)
+		arch_entries++;
+
+	arch_policy_entry = kcalloc(arch_entries + 1,
+				    sizeof(*arch_policy_entry), GFP_KERNEL);
+	if (!arch_policy_entry)
+		return 0;
+
+	/* Convert each policy string rules to struct ima_rule_entry format */
+	for (rules = arch_rules, i = 0; *rules != NULL; rules++) {
+		char rule[255];
+		int result;
+
+		result = strlcpy(rule, *rules, sizeof(rule));
+
+		INIT_LIST_HEAD(&arch_policy_entry[i].list);
+		result = ima_parse_rule(rule, &arch_policy_entry[i]);
+		if (result) {
+			pr_warn("Skipping unknown architecture policy rule: %s\n",
+				rule);
+			memset(&arch_policy_entry[i], 0,
+			       sizeof(*arch_policy_entry));
+			continue;
+		}
+		i++;
+	}
+	return i;
+}
+
 /**
  * ima_init_policy - initialize the default measure rules.
  *
@@ -509,7 +556,7 @@ static void add_rules(struct ima_rule_entry *entries, int count,
  */
 void __init ima_init_policy(void)
 {
-	int build_appraise_entries;
+	int build_appraise_entries, arch_entries;
 
 	/* if !ima_policy, we load NO default rules */
 	if (ima_policy)
@@ -530,9 +577,22 @@ void __init ima_init_policy(void)
 		break;
 	}
 
+	/*
+	 * Based on runtime secure boot flags, insert arch specific measurement
+	 * and appraise rules requiring file signatures for both the initial
+	 * and custom policies, prior to other appraise rules.
+	 * (Highest priority)
+	 */
+	arch_entries = ima_init_arch_policy();
+	if (!arch_entries)
+		pr_info("No architecture policies found\n");
+	else
+		add_rules(arch_policy_entry, arch_entries,
+			  IMA_DEFAULT_POLICY | IMA_CUSTOM_POLICY);
+
 	/*
 	 * Insert the builtin "secure_boot" policy rules requiring file
-	 * signatures, prior to any other appraise rules.
+	 * signatures, prior to other appraise rules.
 	 */
 	if (ima_use_secure_boot)
 		add_rules(secure_boot_rules, ARRAY_SIZE(secure_boot_rules),
@@ -591,6 +651,14 @@ void ima_update_policy(void)
 	if (ima_rules != policy) {
 		ima_policy_flag = 0;
 		ima_rules = policy;
+
+		/*
+		 * IMA architecture specific policy rules are specified
+		 * as strings and converted to an array of ima_entry_rules
+		 * on boot.  After loading a custom policy, free the
+		 * architecture specific rules stored as an array.
+		 */
+		kfree(arch_policy_entry);
 	}
 	ima_update_policy_flag();
 }