logging: Fix runtime message creation in user-mode thread

The runtime message creation (CONFIG_LOG_ALWAYS_RUNTIME=y) in a user-
mode thread raises a MPU violation, e.g. call LOG_INF("Test") in a
user-mode thread.

The function 'z_log_msg_runtime_vcreate' runs in user mode but works
with Kernel data. Hence, create the cbprintf package on the stack (of
the user mode thread) and pass it further to the syscall
'z_log_msg_static_create'.

Signed-off-by: Christoph Winklhofer <[email protected]>

Author: cjwinklhofer

subsys/logging/log_msg.c

@@ -372,7 +372,10 @@ void z_log_msg_runtime_vcreate(uint8_t domain_id, const void *source,
 	struct log_msg_desc desc =
 		Z_LOG_MSG_DESC_INITIALIZER(domain_id, level, plen, dlen);
 
-	if (IS_ENABLED(CONFIG_LOG_MODE_DEFERRED) && BACKENDS_IN_USE()) {
+	if (IS_ENABLED(CONFIG_USERSPACE) && k_is_user_context()) {
+		pkg = alloca(plen);
+		msg = NULL;
+	} else if (IS_ENABLED(CONFIG_LOG_MODE_DEFERRED) && BACKENDS_IN_USE()) {
 		msg = z_log_msg_alloc(msg_wlen);
 		if (IS_ENABLED(CONFIG_LOG_FRONTEND) && msg == NULL) {
 			pkg = alloca(plen);
@@ -389,12 +392,17 @@ void z_log_msg_runtime_vcreate(uint8_t domain_id, const void *source,
 		__ASSERT_NO_MSG(plen >= 0);
 	}
 
-	if (IS_ENABLED(CONFIG_LOG_FRONTEND) && frontend_runtime_filtering(source, desc.level)) {
-		log_frontend_msg(source, desc, pkg, data);
-	}
+	if (IS_ENABLED(CONFIG_USERSPACE) && k_is_user_context()) {
+		z_log_msg_static_create(source, desc, pkg, data);
+	} else {
+		if (IS_ENABLED(CONFIG_LOG_FRONTEND) &&
+		    frontend_runtime_filtering(source, desc.level)) {
+			log_frontend_msg(source, desc, pkg, data);
+		}
 
-	if (BACKENDS_IN_USE()) {
-		z_log_msg_finalize(msg, source, desc, data);
+		if (BACKENDS_IN_USE()) {
+			z_log_msg_finalize(msg, source, desc, data);
+		}
 	}
 }
 EXPORT_SYMBOL(z_log_msg_runtime_vcreate);