[PATCH v6 1/4] IMA: Add func to measure LSM state and policy

Lakshmi Ramasubramanian
2020-08-05T00:43:42Z

Critical data structures of security modules need to be measured to
enable an attestation service to verify if the configuration and
policies for the security modules have been setup correctly and
that they haven't been tampered with at runtime. A new IMA policy is
required for handling this measurement.

Define two new IMA policy func namely LSM_STATE and LSM_POLICY to
measure the state and the policy provided by the security modules.
Update ima_match_rules() and ima_validate_rule() to check for
the new func and ima_parse_rule() to handle the new func.

Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
---
Documentation/ABI/testing/ima_policy | 9 ++++++++
security/integrity/ima/ima.h | 2 ++
security/integrity/ima/ima_api.c | 2 +-
security/integrity/ima/ima_policy.c | 34 ++++++++++++++++++++++++----
4 files changed, 42 insertions(+), 5 deletions(-)

diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
index cd572912c593..b7c7fb548c0c 100644
--- a/Documentation/ABI/testing/ima_policy
+++ b/Documentation/ABI/testing/ima_policy
@@ -30,6 +30,7 @@ Description:
[FIRMWARE_CHECK]
[KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK]
[KEXEC_CMDLINE] [KEY_CHECK]
+ [LSM_STATE] [LSM_POLICY]
mask:= [[^]MAY_READ] [[^]MAY_WRITE] [[^]MAY_APPEND]
[[^]MAY_EXEC]
fsmagic:= hex value
@@ -125,3 +126,11 @@ Description:
keys added to .builtin_trusted_keys or .ima keyring:

measure func=KEY_CHECK keyrings=.builtin_trusted_keys|.ima
+
+ Example of measure rule using LSM_STATE to measure LSM state:
+
+ measure func=LSM_STATE template=ima-buf
+
+ Example of measure rule using LSM_POLICY to measure LSM policy:
+
+ measure func=LSM_POLICY template=ima-ng
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 38043074ce5e..1b5f4b2f17d0 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -200,6 +200,8 @@ static inline unsigned int ima_hash_key(u8 *digest)
hook(POLICY_CHECK, policy) \
hook(KEXEC_CMDLINE, kexec_cmdline) \
hook(KEY_CHECK, key) \
+ hook(LSM_STATE, lsm_state) \
+ hook(LSM_POLICY, lsm_policy) \
hook(MAX_CHECK, none)

#define __ima_hook_enumify(ENUM, str) ENUM,
diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index 4f39fb93f278..8c8b4e4a6493 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -176,7 +176,7 @@ void ima_add_violation(struct file *file, const unsigned char *filename,
* subj=, obj=, type=, func=, mask=, fsmagic=
* subj,obj, and type: are LSM specific.
* func: FILE_CHECK | BPRM_CHECK | CREDS_CHECK | MMAP_CHECK | MODULE_CHECK
- * | KEXEC_CMDLINE | KEY_CHECK
+ * | KEXEC_CMDLINE | KEY_CHECK | LSM_STATE | LSM_POLICY
* mask: contains the permission mask
* fsmagic: hex value
*
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 07f033634b27..e4de581442d5 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -442,13 +442,21 @@ static bool ima_match_rules(struct ima_rule_entry *rule, struct inode *inode,
{
int i;

- if (func == KEY_CHECK) {
- return (rule->flags & IMA_FUNC) && (rule->func == func) &&
- ima_match_keyring(rule, keyring, cred);
- }
if ((rule->flags & IMA_FUNC) &&
(rule->func != func && func != POST_SETATTR))
return false;
+
+ switch (func) {
+ case KEY_CHECK:
+ return ((rule->func == func) &&
+ ima_match_keyring(rule, keyring, cred));
+ case LSM_STATE:
+ case LSM_POLICY:
+ return (rule->func == func);
+ default:
+ break;
+ }
+
if ((rule->flags & IMA_MASK) &&
(rule->mask != mask && func != POST_SETATTR))
return false;
@@ -1044,6 +1052,18 @@ static bool ima_validate_rule(struct ima_rule_entry *entry)
if (ima_rule_contains_lsm_cond(entry))
return false;

+ break;
+ case LSM_STATE:
+ case LSM_POLICY:
+ if (entry->action & ~(MEASURE | DONT_MEASURE))
+ return false;
+
+ if (entry->flags & ~(IMA_FUNC | IMA_PCR))
+ return false;
+
+ if (ima_rule_contains_lsm_cond(entry))
+ return false;
+
break;
default:
return false;
@@ -1176,6 +1196,12 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
entry->func = KEXEC_CMDLINE;
else if (strcmp(args[0].from, "KEY_CHECK") == 0)
entry->func = KEY_CHECK;
+ else if (IS_ENABLED(CONFIG_SECURITY_SELINUX) &&
+ strcmp(args[0].from, "LSM_STATE") == 0)
+ entry->func = LSM_STATE;
+ else if (IS_ENABLED(CONFIG_SECURITY_SELINUX) &&
+ strcmp(args[0].from, "LSM_POLICY") == 0)
+ entry->func = LSM_POLICY;
else
result = -EINVAL;
if (!result)
--
2.27.0