linux-kernel - [RFC][PATCH v2 5/9] ima: Modify existing boot-time built-in policies with digest cache policies

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Date: Mon, 15 Apr 2024 18:10:40 +0200
From: Roberto Sassu <roberto.sassu@...weicloud.com>
To: corbet@....net,
	zohar@...ux.ibm.com,
	dmitry.kasatkin@...il.com,
	eric.snowberg@...cle.com,
	paul@...l-moore.com,
	jmorris@...ei.org,
	serge@...lyn.com
Cc: linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org,
	linux-integrity@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	wufan@...ux.microsoft.com,
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	hch@....de,
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	petr.vorel@...il.com,
	mzerqung@...inter.de,
	kgold@...ux.ibm.com,
	Roberto Sassu <roberto.sassu@...wei.com>
Subject: [RFC][PATCH v2 5/9] ima: Modify existing boot-time built-in policies with digest cache policies

From: Roberto Sassu <roberto.sassu@...wei.com>

Setting the boot-time built-in policies 'digest_cache_measure' and
'digest_cache_appraise' is not sufficient to use the digest_cache LSM to
measure and appraise files, since their effect is only to measure and
appraise digest lists.

Modify existing measurement rules if the 'digest_cache_measure' built-in
policy is specified by adding to them:

digest_cache=data pcr=12

Other than enabling the usage of the digest_cache LSM for measurement, the
additional keywords also store measurements in the PCR 12, to not confuse
new style measurements with the original ones still stored on PCR 10.

Modify existing appraisal rules if the 'digest_cache_appraise' built-in
policy is specified by adding to them:

digest_cache=data

The additional keyword enables the usage of digest_cache LSM for appraisal.

Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
---
 Documentation/admin-guide/kernel-parameters.txt |  9 +++++++--
 security/integrity/ima/ima_policy.c             | 14 ++++++++++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index df877588decc..dc96e6f4eb40 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2074,11 +2074,16 @@
 			critical data.
 
 			The "digest_cache_measure" policy measures digest lists
-			into PCR 12 (can be changed with kernel config).
+			into PCR 12 (can be changed with kernel config), enables
+			the digest cache to be used for the other selected
+			measure rules (if compatible), and measures the files
+			with digest not found in the digest list into PCR 12
+			(changeable).
 
 			The "digest_cache_appraise" policy appraises digest
 			lists with IMA signatures or module-style appended
-			signatures.
+			signatures, and enables the digest cache to be used for
+			the other selected appraise rules (if compatible).
 
 	ima_tcb		[IMA] Deprecated.  Use ima_policy= instead.
 			Load a policy which meets the needs of the Trusted
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index f049543f6b64..21bd7a123548 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -918,6 +918,20 @@ static void add_rules(struct ima_rule_entry *entries, int count,
 	for (i = 0; i < count; i++) {
 		struct ima_rule_entry *entry;
 
+		if (IS_ENABLED(CONFIG_SECURITY_DIGEST_CACHE) &&
+		    entries[i].action == MEASURE && ima_digest_cache_measure &&
+		    ima_digest_cache_func_allowed(&entries[i])) {
+			entries[i].digest_cache_usage |= IMA_DIGEST_CACHE_MEASURE_DATA;
+			entries[i].pcr = CONFIG_IMA_DIGEST_CACHE_MEASURE_PCR_IDX;
+			entries[i].flags |= IMA_PCR;
+		}
+
+		if (IS_ENABLED(CONFIG_SECURITY_DIGEST_CACHE) &&
+		    entries[i].action == APPRAISE &&
+		    ima_digest_cache_appraise &&
+		    ima_digest_cache_func_allowed(&entries[i]))
+			entries[i].digest_cache_usage |= IMA_DIGEST_CACHE_APPRAISE_DATA;
+
 		if (policy_rule & IMA_DEFAULT_POLICY)
 			list_add_tail(&entries[i].list, &ima_default_rules);
 
-- 
2.34.1