apparmor: add parameter to control whether policy hashing is used

Signed-off-by: John Johansen <john.johansen@canonical.com>
Acked-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Seth Arnold <seth.arnold@canonical.com>

security/apparmor/Kconfig

@@ -31,13 +31,26 @@ config SECURITY_APPARMOR_BOOTPARAM_VALUE
 	  If you are unsure how to answer this question, answer 1.
 
 config SECURITY_APPARMOR_HASH
-	bool "SHA1 hash of loaded profiles"
+	bool "Enable introspection of sha1 hashes for loaded profiles"
 	depends on SECURITY_APPARMOR
 	select CRYPTO
 	select CRYPTO_SHA1
 	default y
 
 	help
-	  This option selects whether sha1 hashing is done against loaded
-          profiles and exported for inspection to user space via the apparmor
-          filesystem.
+	  This option selects whether introspection of loaded policy
+	  is available to userspace via the apparmor filesystem.
+
+config SECURITY_APPARMOR_HASH_DEFAULT
+       bool "Enable policy hash introspection by default"
+       depends on SECURITY_APPARMOR_HASH
+       default y
+
+       help
+         This option selects whether sha1 hashing of loaded policy
+	 is enabled by default. The generation of sha1 hashes for
+	 loaded policy provide system administrators a quick way
+	 to verify that policy in the kernel matches what is expected,
+	 however it can slow down policy load on some devices. In
+	 these cases policy hashing can be disabled by default and
+	 enabled only if needed.

security/apparmor/include/apparmor.h

@@ -37,6 +37,7 @@
 extern enum audit_mode aa_g_audit;
 extern bool aa_g_audit_header;
 extern bool aa_g_debug;
+extern bool aa_g_hash_policy;
 extern bool aa_g_lock_policy;
 extern bool aa_g_logsyscall;
 extern bool aa_g_paranoid_load;

security/apparmor/lsm.c

@@ -669,6 +669,10 @@ enum profile_mode aa_g_profile_mode = APPARMOR_ENFORCE;
 module_param_call(mode, param_set_mode, param_get_mode,
 		  &aa_g_profile_mode, S_IRUSR | S_IWUSR);
 
+/* whether policy verification hashing is enabled */
+bool aa_g_hash_policy = CONFIG_SECURITY_APPARMOR_HASH_DEFAULT;
+module_param_named(hash_policy, aa_g_hash_policy, aabool, S_IRUSR | S_IWUSR);
+
 /* Debug mode */
 bool aa_g_debug;
 module_param_named(debug, aa_g_debug, aabool, S_IRUSR | S_IWUSR);

security/apparmor/policy_unpack.c

@@ -775,8 +775,9 @@ int aa_unpack(void *udata, size_t size, struct list_head *lh, const char **ns)
 		if (error)
 			goto fail_profile;
 
-		error = aa_calc_profile_hash(profile, e.version, start,
-					     e.pos - start);
+		if (aa_g_hash_policy)
+			error = aa_calc_profile_hash(profile, e.version, start,
+						     e.pos - start);
 		if (error)
 			goto fail_profile;