[PATCH v4 5/6] ima: require signature based appraisal

[Dmitry Kasatkin]

This patch provides CONFIG_IMA_APPRAISE_SIGNED_INIT kernel configuration
option to force IMA appraisal using signatures. This is useful, when EVM
key is not initialized yet and we want securely initialize integrity or
any other functionality.

It forces embedded policy to require signature. Signed initialization
script can initialize EVM key, update the IMA policy and change further
requirement of everything to be signed.

Changes in v3:
* kernel parameter fixed to configuration option in the patch description

Changes in v2:
* policy change of this patch separated from the key loading patch

Signed-off-by: Dmitry Kasatkin <d.kasatkin@xxxxxxxxxxx>
---
 security/integrity/ima/Kconfig      | 7 +++++++
 security/integrity/ima/ima_policy.c | 5 +++++
 2 files changed, 12 insertions(+)

diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index 8288edc..31b44b8 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -146,3 +146,10 @@ config IMA_X509_PATH
 	default "/etc/keys/x509_ima.der"
 	help
 	   This option defines IMA X509 certificate path.
+
+config IMA_APPRAISE_SIGNED_INIT
+	bool "Require signed user-space initialization"
+	depends on IMA_LOAD_X509
+	default n
+	help
+	   This option requires user-space init to be signed.
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 0d14d25..222ff79 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -100,7 +100,12 @@ static struct ima_rule_entry default_appraise_rules[] = {
 	{.action = DONT_APPRAISE, .fsmagic = SECURITYFS_MAGIC, .flags = IMA_FSMAGIC},
 	{.action = DONT_APPRAISE, .fsmagic = SELINUX_MAGIC, .flags = IMA_FSMAGIC},
 	{.action = DONT_APPRAISE, .fsmagic = CGROUP_SUPER_MAGIC, .flags = IMA_FSMAGIC},
+#ifndef CONFIG_IMA_APPRAISE_SIGNED_INIT
 	{.action = APPRAISE, .fowner = GLOBAL_ROOT_UID, .flags = IMA_FOWNER},
+#else
+	/* force signature */
+	{.action = APPRAISE, .fowner = GLOBAL_ROOT_UID, .flags = IMA_FOWNER | IMA_DIGSIG_REQUIRED},
+#endif
 };
 
 static LIST_HEAD(ima_default_rules);
-- 
1.9.1

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