[RFC][PATCH v4 3/9] ima: Add digest_cache_measure/appraise boot-time built-in policies

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu at huawei.com>

Specify the 'digest_cache_measure' boot-time policy with 'ima_policy=' in
the kernel command line to add the following rule at the beginning of the
IMA policy, before other rules:

measure func=DIGEST_LIST_CHECK pcr=12

which will measure digest lists into PCR 12 (or the value in
CONFIG_IMA_DIGEST_CACHE_MEASURE_PCR_IDX).

Specify 'digest_cache_appraise' to add the following rule at the beginning,
before other rules:

appraise func=DIGEST_LIST_CHECK appraise_type=imasig|modsig

which will appraise digest lists with IMA signatures or module-style
appended signatures.

Adding those rules at the beginning rather than at the end is necessary to
ensure that digest lists are measured and appraised in the initial ram
disk, which would be otherwise prevented by the dont_ rules.

Signed-off-by: Roberto Sassu <roberto.sassu at huawei.com>
---
 .../admin-guide/kernel-parameters.txt         | 10 +++++-
 security/integrity/ima/Kconfig                | 10 ++++++
 security/integrity/ima/ima_policy.c           | 35 +++++++++++++++++++
 3 files changed, 54 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 1518343bbe22..9b6f85b1376c 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2094,7 +2094,8 @@
 	ima_policy=	[IMA]
 			The builtin policies to load during IMA setup.
 			Format: "tcb | appraise_tcb | secure_boot |
-				 fail_securely | critical_data"
+				 fail_securely | critical_data |
+				 digest_cache_measure | digest_cache_appraise"
 
 			The "tcb" policy measures all programs exec'd, files
 			mmap'd for exec, and all files opened with the read
@@ -2116,6 +2117,13 @@
 			The "critical_data" policy measures kernel integrity
 			critical data.
 
+			The "digest_cache_measure" policy measures digest lists
+			into PCR 12 (can be changed with kernel config).
+
+			The "digest_cache_appraise" policy appraises digest
+			lists with IMA signatures or module-style appended
+			signatures.
+
 	ima_tcb		[IMA] Deprecated.  Use ima_policy= instead.
 			Load a policy which meets the needs of the Trusted
 			Computing Base.  This means IMA will measure all
diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index 475c32615006..d2d79185f714 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -321,4 +321,14 @@ config IMA_DISABLE_HTABLE
 	help
 	   This option disables htable to allow measurement of duplicate records.
 
+config IMA_DIGEST_CACHE_MEASURE_PCR_IDX
+	int
+	range 8 14
+	default 12
+	help
+	  This option determines the TPM PCR register index that IMA uses to
+	  maintain the integrity aggregate of the measurement list, when the
+	  Integrity Digest Cache is used (different measurement style).
+	  If unsure, use the default 12.
+
 endif
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index eb3bfe01782d..c2bf58010b89 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -254,6 +254,21 @@ static struct ima_rule_entry critical_data_rules[] __ro_after_init = {
 	{.action = MEASURE, .func = CRITICAL_DATA, .flags = IMA_FUNC},
 };
 
+static struct ima_rule_entry measure_digest_cache_rule __ro_after_init = {
+#ifdef CONFIG_INTEGRITY_DIGEST_CACHE
+	.action = MEASURE, .func = DIGEST_LIST_CHECK,
+	.pcr = CONFIG_IMA_DIGEST_CACHE_MEASURE_PCR_IDX,
+	.flags = IMA_FUNC | IMA_PCR
+#endif
+};
+
+static struct ima_rule_entry appraise_digest_cache_rule __ro_after_init = {
+#ifdef CONFIG_INTEGRITY_DIGEST_CACHE
+	.action = APPRAISE, .func = DIGEST_LIST_CHECK,
+	.flags = IMA_FUNC | IMA_DIGSIG_REQUIRED | IMA_MODSIG_ALLOWED,
+#endif
+};
+
 /* An array of architecture specific rules */
 static struct ima_rule_entry *arch_policy_entry __ro_after_init;
 
@@ -278,6 +293,8 @@ static bool ima_use_appraise_tcb __initdata;
 static bool ima_use_secure_boot __initdata;
 static bool ima_use_critical_data __initdata;
 static bool ima_fail_unverifiable_sigs __ro_after_init;
+static bool ima_digest_cache_measure __ro_after_init;
+static bool ima_digest_cache_appraise __ro_after_init;
 static int __init policy_setup(char *str)
 {
 	char *p;
@@ -295,6 +312,10 @@ static int __init policy_setup(char *str)
 			ima_use_critical_data = true;
 		else if (strcmp(p, "fail_securely") == 0)
 			ima_fail_unverifiable_sigs = true;
+		else if (strcmp(p, "digest_cache_measure") == 0)
+			ima_digest_cache_measure = true;
+		else if (strcmp(p, "digest_cache_appraise") == 0)
+			ima_digest_cache_appraise = true;
 		else
 			pr_err("policy \"%s\" not found", p);
 	}
@@ -983,6 +1004,20 @@ void __init ima_init_policy(void)
 {
 	int build_appraise_entries, arch_entries;
 
+	/*
+	 * We need to load digest cache rules at the beginning, to avoid dont_
+	 * rules causing ours to not be reached.
+	 */
+	if (IS_ENABLED(CONFIG_INTEGRITY_DIGEST_CACHE)) {
+		if (ima_digest_cache_measure)
+			add_rules(&measure_digest_cache_rule, 1,
+				  IMA_DEFAULT_POLICY);
+
+		if (ima_digest_cache_appraise)
+			add_rules(&appraise_digest_cache_rule, 1,
+				  IMA_DEFAULT_POLICY);
+	}
+
 	/* if !ima_policy, we load NO default rules */
 	if (ima_policy)
 		add_rules(dont_measure_rules, ARRAY_SIZE(dont_measure_rules),
-- 
2.47.0.118.gfd3785337b