ima: define a set of appraisal rules requiring file signatures

The builtin "ima_appraise_tcb" policy should require file signatures for
at least a few of the hooks (eg. kernel modules, firmware, and the kexec
kernel image), but changing it would break the existing userspace/kernel
ABI.

This patch defines a new builtin policy named "secure_boot", which
can be specified on the "ima_policy=" boot command line, independently
or in conjunction with the "ima_appraise_tcb" policy, by specifing
ima_policy="appraise_tcb | secure_boot".  The new appraisal rules
requiring file signatures will be added prior to the "ima_appraise_tcb"
rules.

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

Changelog:
- Reference secure boot in the new builtin policy name. (Thiago Bauermann)

1 files changed, 25 insertions, 1 deletions

diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 0ddc41389a9c..3653c86c70df 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -153,6 +153,17 @@ static struct ima_rule_entry default_appraise_rules[] __ro_after_init = {
 #endif
 };
 
+static struct ima_rule_entry secure_boot_rules[] __ro_after_init = {
+        {.action = APPRAISE, .func = MODULE_CHECK,
+         .flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
+        {.action = APPRAISE, .func = FIRMWARE_CHECK,
+         .flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
+        {.action = APPRAISE, .func = KEXEC_KERNEL_CHECK,
+         .flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
+        {.action = APPRAISE, .func = POLICY_CHECK,
+         .flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},
+};
+
 static LIST_HEAD(ima_default_rules);
 static LIST_HEAD(ima_policy_rules);
 static LIST_HEAD(ima_temp_rules);
@@ -171,6 +182,7 @@ 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_secure_boot __initdata;
 static int __init policy_setup(char *str)
 {
         char *p;
@@ -182,6 +194,8 @@ static int __init policy_setup(char *str)
                         ima_policy = DEFAULT_TCB;
                 else if (strcmp(p, "appraise_tcb") == 0)
                         ima_use_appraise_tcb = 1;
+                else if (strcmp(p, "secure_boot") == 0)
+                        ima_use_secure_boot = 1;
         }
 
         return 1;
@@ -410,12 +424,14 @@ void ima_update_policy_flag(void)
  */
 void __init ima_init_policy(void)
 {
-        int i, measure_entries, appraise_entries;
+        int i, measure_entries, appraise_entries, secure_boot_entries;
 
         /* if !ima_policy set entries = 0 so we load NO default rules */
         measure_entries = ima_policy ? ARRAY_SIZE(dont_measure_rules) : 0;
         appraise_entries = ima_use_appraise_tcb ?
                          ARRAY_SIZE(default_appraise_rules) : 0;
+        secure_boot_entries = ima_use_secure_boot ?
+                        ARRAY_SIZE(secure_boot_rules) : 0;
 
         for (i = 0; i < measure_entries; i++)
                 list_add_tail(&dont_measure_rules[i].list, &ima_default_rules);
@@ -434,6 +450,14 @@ void __init ima_init_policy(void)
                 break;
         }
 
+        /*
+         * Insert the appraise rules requiring file signatures, prior to
+         * any other appraise rules.
+         */
+        for (i = 0; i < secure_boot_entries; i++)
+                list_add_tail(&secure_boot_rules[i].list,
+                              &ima_default_rules);
+
         for (i = 0; i < appraise_entries; i++) {
                 list_add_tail(&default_appraise_rules[i].list,
                               &ima_default_rules);