ima: require signature based appraisal

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@samsung.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

2 files changed, 13 insertions, 0 deletions

diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index b0840f9a552f..b80a93ec1ccc 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -149,3 +149,10 @@ 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 0d14d2591805..d1eefb9d65fb 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -100,7 +100,13 @@ 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);