ima: Introduce appraise_exec_tcb policy

hulk inclusion
category: feature
feature: IMA Digest Lists extension
bugzilla: 46797

-------------------------------------------------

This patch introduces a new hard-coded policy to appraise executable code:

appraise func=MODULE_CHECK appraise_type=imasig
appraise func=FIRMWARE_CHECK appraise_type=imasig
appraise func=KEXEC_KERNEL_CHECK appraise_type=imasig
appraise func=POLICY_CHECK appraise_type=imasig
appraise func=DIGEST_LIST_CHECK appraise_type=imasig
dont_appraise fsmagic=0x9fa0
dont_appraise fsmagic=0x62656572
dont_appraise fsmagic=0x64626720
dont_appraise fsmagic=0x858458f6
dont_appraise fsmagic=0x1cd1
dont_appraise fsmagic=0x42494e4d
dont_appraise fsmagic=0x73636673
dont_appraise fsmagic=0xf97cff8c
dont_appraise fsmagic=0x43415d53
dont_appraise fsmagic=0x6e736673
dont_appraise fsmagic=0xde5e81e4
dont_appraise fsmagic=0x27e0eb
dont_appraise fsmagic=0x63677270
appraise func=BPRM_CHECK appraise_type=imasig
appraise func=MMAP_CHECK appraise_type=imasig

The new policy can be selected by specifying ima_policy=appraise_exec_tcb
in the kernel command line.
Signed-off-by: NRoberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: NTianxing Zhang <zhangtianxing3@huawei.com>
Reviewed-by: NJason Yan <yanaijie@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

Documentation/admin-guide/kernel-parameters.txt

@@ -1793,6 +1793,11 @@
 			of files (eg. kexec kernel image, kernel modules,
 			firmware, policy, etc) based on file signatures.
 
+			The "appraise_exec_tcb" includes the "secure_boot"
+			policy and additionally includes all programs exec'd and
+			files mmap'd for exec. Files in the tmpfs filesystem are
+			not excluded from appraisal.
+
 			The "fail_securely" policy forces file signature
 			verification failure also on privileged mounted
 			filesystems with the SB_I_UNVERIFIABLE_SIGNATURE

security/integrity/ima/ima_policy.c

@@ -175,6 +175,13 @@ static struct ima_rule_entry default_appraise_rules[] __ro_after_init = {
 #endif
 };
 
+static struct ima_rule_entry appraise_exec_rules[] __ro_after_init = {
+	{.action = APPRAISE, .func = BPRM_CHECK,
+	 .flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
+	{.action = APPRAISE, .func = MMAP_CHECK,
+	 .flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
+};
+
 static struct ima_rule_entry build_appraise_rules[] __ro_after_init = {
 #ifdef CONFIG_IMA_APPRAISE_REQUIRE_MODULE_SIGS
 	{.action = APPRAISE, .func = MODULE_CHECK,
@@ -228,6 +235,7 @@ static int __init default_measure_policy_setup(char *str)
 __setup("ima_tcb", default_measure_policy_setup);
 
 static bool ima_use_appraise_tcb __initdata;
+static bool ima_use_appraise_exec_tcb __initdata;
 static bool ima_use_secure_boot __initdata;
 static bool ima_fail_unverifiable_sigs __ro_after_init;
 static int __init policy_setup(char *str)
@@ -243,6 +251,8 @@ static int __init policy_setup(char *str)
 			ima_policy = EXEC_TCB;
 		else if (strcmp(p, "appraise_tcb") == 0)
 			ima_use_appraise_tcb = true;
+		else if (strcmp(p, "appraise_exec_tcb") == 0)
+			ima_use_appraise_exec_tcb = true;
 		else if (strcmp(p, "secure_boot") == 0)
 			ima_use_secure_boot = true;
 		else if (strcmp(p, "fail_securely") == 0)
@@ -731,6 +741,15 @@ static void __init add_rules(struct ima_rule_entry *entries, int count,
 					continue;
 		}
 
+		if (ima_use_appraise_exec_tcb) {
+			if (entries == default_appraise_rules) {
+				if (entries[i].action != DONT_APPRAISE)
+					continue;
+				if ((entries[i].flags & IMA_FSMAGIC) &&
+				    entries[i].fsmagic == TMPFS_MAGIC)
+					continue;
+			}
+		}
 		if (policy_rule & IMA_DEFAULT_POLICY)
 			list_add_tail(&entries[i].list, &ima_default_rules);
 
@@ -844,7 +863,7 @@ void __init ima_init_policy(void)
 	 * Insert the builtin "secure_boot" policy rules requiring file
 	 * signatures, prior to other appraise rules.
 	 */
-	if (ima_use_secure_boot)
+	if (ima_use_secure_boot || ima_use_appraise_exec_tcb)
 		add_rules(secure_boot_rules, ARRAY_SIZE(secure_boot_rules),
 			  IMA_DEFAULT_POLICY);
 
@@ -864,11 +883,16 @@ void __init ima_init_policy(void)
 				  IMA_DEFAULT_POLICY | IMA_CUSTOM_POLICY);
 	}
 
-	if (ima_use_appraise_tcb)
+	if (ima_use_appraise_tcb || ima_use_appraise_exec_tcb)
 		add_rules(default_appraise_rules,
 			  ARRAY_SIZE(default_appraise_rules),
 			  IMA_DEFAULT_POLICY);
 
+	if (ima_use_appraise_exec_tcb)
+		add_rules(appraise_exec_rules,
+			  ARRAY_SIZE(appraise_exec_rules),
+			  IMA_DEFAULT_POLICY);
+
 	ima_update_policy_flag();
 }