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From: Roberto Sassu <roberto.sassu@huaweicloud.com>
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	Roberto Sassu <roberto.sassu@huawei.com>
Subject: [RFC][PATCH v2 4/9] ima: Add digest_cache_measure/appraise boot-time built-in policies
Date: Mon, 15 Apr 2024 18:10:39 +0200
Message-Id: <20240415161044.2572438-5-roberto.sassu@huaweicloud.com>
In-Reply-To: <20240415161044.2572438-1-roberto.sassu@huaweicloud.com>
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From: Roberto Sassu <roberto.sassu@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 rule 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@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 902ecd92a29f..df877588decc 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2050,7 +2050,8 @@
 	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
@@ -2072,6 +2073,13 @@
 			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..6a481019fb6e 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
+	  digest_cache LSM 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 9e13b88b0ed5..f049543f6b64 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_SECURITY_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_SECURITY_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);
 	}
@@ -971,6 +992,20 @@ 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_SECURITY_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),
-- 
2.34.1