linux-kernel - [PATCH v5 6/7] IMA: add critical_data to the built-in policy rules

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Date:   Sun,  1 Nov 2020 14:26:25 -0800
From:   Tushar Sugandhi <tusharsu@...ux.microsoft.com>
To:     zohar@...ux.ibm.com, stephen.smalley.work@...il.com,
        casey@...aufler-ca.com, agk@...hat.com, snitzer@...hat.com,
        gmazyland@...il.com, paul@...l-moore.com
Cc:     tyhicks@...ux.microsoft.com, sashal@...nel.org, jmorris@...ei.org,
        nramas@...ux.microsoft.com, linux-integrity@...r.kernel.org,
        selinux@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, dm-devel@...hat.com
Subject: [PATCH v5 6/7] IMA: add critical_data to the built-in policy rules

From: Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>

The IMA hook to measure kernel critical data, namely
ima_measure_critical_data(), could be called before a custom IMA policy
is loaded. For example, SELinux calls ima_measure_critical_data() to
measure its state and policy when they are initialized. This occurs
before a custom IMA policy is loaded, and hence IMA hook will not
measure the data. A built-in policy is therefore needed to measure
critical data provided by callers before a custom IMA policy is loaded.

Add CRITICAL_DATA to built-in IMA rules if the kernel command line
contains "ima_policy=critical_data". Set the IMA template for this rule
to "ima-buf" since ima_measure_critical_data() measures a buffer.

Signed-off-by: Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
---
 security/integrity/ima/ima_policy.c | 32 +++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index ec99e0bb6c6f..dc8fe969d3fe 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -206,6 +206,10 @@ static struct ima_rule_entry secure_boot_rules[] __ro_after_init = {
 	 .flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
 };
 
+static struct ima_rule_entry critical_data_rules[] __ro_after_init = {
+	{.action = MEASURE, .func = CRITICAL_DATA, .flags = IMA_FUNC},
+};
+
 /* An array of architecture specific rules */
 static struct ima_rule_entry *arch_policy_entry __ro_after_init;
 
@@ -228,6 +232,7 @@ __setup("ima_tcb", default_measure_policy_setup);
 
 static bool ima_use_appraise_tcb __initdata;
 static bool ima_use_secure_boot __initdata;
+static bool ima_use_critical_data __ro_after_init;
 static bool ima_fail_unverifiable_sigs __ro_after_init;
 static int __init policy_setup(char *str)
 {
@@ -242,6 +247,8 @@ static int __init policy_setup(char *str)
 			ima_use_appraise_tcb = true;
 		else if (strcmp(p, "secure_boot") == 0)
 			ima_use_secure_boot = true;
+		else if (strcmp(p, "critical_data") == 0)
+			ima_use_critical_data = true;
 		else if (strcmp(p, "fail_securely") == 0)
 			ima_fail_unverifiable_sigs = true;
 		else
@@ -813,6 +820,8 @@ static int __init ima_init_arch_policy(void)
 void __init ima_init_policy(void)
 {
 	int build_appraise_entries, arch_entries;
+	struct ima_template_desc *template = NULL;
+	int ret = 0;
 
 	/* if !ima_policy, we load NO default rules */
 	if (ima_policy)
@@ -875,6 +884,29 @@ void __init ima_init_policy(void)
 			  ARRAY_SIZE(default_appraise_rules),
 			  IMA_DEFAULT_POLICY);
 
+	if (ima_use_critical_data) {
+		template = lookup_template_desc("ima-buf");
+		if (!template) {
+			ret = -EINVAL;
+			goto out;
+		}
+
+		ret = template_desc_init_fields(template->fmt,
+						&(template->fields),
+						&(template->num_fields));
+		if (ret)
+			goto out;
+
+		critical_data_rules[0].template = template;
+		add_rules(critical_data_rules,
+			  ARRAY_SIZE(critical_data_rules),
+			  IMA_DEFAULT_POLICY);
+	}
+
+out:
+	if (ret)
+		pr_err("%s failed, result: %d\n", __func__, ret);
+
 	ima_update_policy_flag();
 }
 
-- 
2.17.1