[PATCH v5 4/5] ima: add support for arch specific policies

[Nayna Jain]

From: Nayna Jain <nayna at linux.ibm.com>

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 at linux.ibm.com>
- Defined function to convert the arch policy strings to an array of
ima_entry_rules.  The memory can then be freed after loading a custom
policy.
- Rename ima_get_arch_policy to arch_get_ima_policy.
Signed-off-by: Mimi Zohar <zohar at linux.ibm.com>
- Modified ima_init_arch_policy() and ima_init_policy() to use add_rules()
from previous patch.
Signed-off-by: Nayna Jain <nayna at linux.ibm.com>
---
 include/linux/ima.h                 |  5 +++
 security/integrity/ima/ima_policy.c | 71 +++++++++++++++++++++++++++++++++++--
 2 files changed, 74 insertions(+), 2 deletions(-)

diff --git a/include/linux/ima.h b/include/linux/ima.h
index 4852255aa4f4..350fa957f8a6 100644
--- a/include/linux/ima.h
+++ b/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)
 {
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 1e30d09a56db..4e435f7561e0 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/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 +505,48 @@ 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 +555,7 @@ 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)
@@ -531,8 +577,21 @@ void __init ima_init_policy(void)
 	}
 
 	/*
+	 * 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 +650,14 @@ 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();
 }
-- 
2.13.6