binder: add BINDER_GET_EXTENDED_ERROR ioctl

Provide a userspace mechanism to pull precise error information upon
failed operations. Extending the current error codes returned by the
interfaces allows userspace to better determine the course of action.
This could be for instance, retrying a failed transaction at a later
point and thus offloading the error handling from the driver.

Acked-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Acked-by: Todd Kjos <tkjos@google.com>
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Link: https://lore.kernel.org/r/20220429235644.697372-3-cmllamas@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/android/binder.c

@@ -147,6 +147,13 @@ module_param_call(stop_on_user_error, binder_set_stop_on_user_error,
 			binder_stop_on_user_error = 2; \
 	} while (0)
 
+#define binder_set_extended_error(ee, _id, _command, _param) \
+	do { \
+		(ee)->id = _id; \
+		(ee)->command = _command; \
+		(ee)->param = _param; \
+	} while (0)
+
 #define to_flat_binder_object(hdr) \
 	container_of(hdr, struct flat_binder_object, hdr)
 
@@ -2708,6 +2715,24 @@ static struct binder_node *binder_get_node_refs_for_txn(
 	return target_node;
 }
 
+static void binder_set_txn_from_error(struct binder_transaction *t, int id,
+				      uint32_t command, int32_t param)
+{
+	struct binder_thread *from = binder_get_txn_from_and_acq_inner(t);
+
+	if (!from) {
+		/* annotation for sparse */
+		__release(&from->proc->inner_lock);
+		return;
+	}
+
+	/* don't override existing errors */
+	if (from->ee.command == BR_OK)
+		binder_set_extended_error(&from->ee, id, command, param);
+	binder_inner_proc_unlock(from->proc);
+	binder_thread_dec_tmpref(from);
+}
+
 static void binder_transaction(struct binder_proc *proc,
 			       struct binder_thread *thread,
 			       struct binder_transaction_data *tr, int reply,
@@ -2753,6 +2778,10 @@ static void binder_transaction(struct binder_proc *proc,
 	e->offsets_size = tr->offsets_size;
 	strscpy(e->context_name, proc->context->name, BINDERFS_MAX_NAME);
 
+	binder_inner_proc_lock(proc);
+	binder_set_extended_error(&thread->ee, t_debug_id, BR_OK, 0);
+	binder_inner_proc_unlock(proc);
+
 	if (reply) {
 		binder_inner_proc_lock(proc);
 		in_reply_to = thread->transaction_stack;
@@ -3498,10 +3527,16 @@ err_invalid_target_handle:
 
 	BUG_ON(thread->return_error.cmd != BR_OK);
 	if (in_reply_to) {
+		binder_set_txn_from_error(in_reply_to, t_debug_id,
+				return_error, return_error_param);
 		thread->return_error.cmd = BR_TRANSACTION_COMPLETE;
 		binder_enqueue_thread_work(thread, &thread->return_error.work);
 		binder_send_failed_reply(in_reply_to, return_error);
 	} else {
+		binder_inner_proc_lock(proc);
+		binder_set_extended_error(&thread->ee, t_debug_id,
+				return_error, return_error_param);
+		binder_inner_proc_unlock(proc);
 		thread->return_error.cmd = return_error;
 		binder_enqueue_thread_work(thread, &thread->return_error.work);
 	}
@@ -4628,6 +4663,7 @@ static struct binder_thread *binder_get_thread_ilocked(
 	thread->return_error.cmd = BR_OK;
 	thread->reply_error.work.type = BINDER_WORK_RETURN_ERROR;
 	thread->reply_error.cmd = BR_OK;
+	thread->ee.command = BR_OK;
 	INIT_LIST_HEAD(&new_thread->waiting_thread_node);
 	return thread;
 }
@@ -5066,6 +5102,25 @@ static int binder_ioctl_get_freezer_info(
 	return 0;
 }
 
+static int binder_ioctl_get_extended_error(struct binder_thread *thread,
+					   void __user *ubuf)
+{
+	struct binder_extended_error *ee = &thread->ee;
+
+	binder_inner_proc_lock(thread->proc);
+	if (copy_to_user(ubuf, ee, sizeof(*ee))) {
+		binder_inner_proc_unlock(thread->proc);
+		return -EFAULT;
+	}
+
+	ee->id = 0;
+	ee->command = BR_OK;
+	ee->param = 0;
+	binder_inner_proc_unlock(thread->proc);
+
+	return 0;
+}
+
 static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	int ret;
@@ -5274,6 +5329,11 @@ static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		binder_inner_proc_unlock(proc);
 		break;
 	}
+	case BINDER_GET_EXTENDED_ERROR:
+		ret = binder_ioctl_get_extended_error(thread, ubuf);
+		if (ret < 0)
+			goto err;
+		break;
 	default:
 		ret = -EINVAL;
 		goto err;

drivers/android/binder_internal.h

@@ -480,6 +480,8 @@ struct binder_proc {
  *                        (only accessed by this thread)
  * @reply_error:          transaction errors reported by target thread
  *                        (protected by @proc->inner_lock)
+ * @ee:                   extended error information from this thread
+ *                        (protected by @proc->inner_lock)
  * @wait:                 wait queue for thread work
  * @stats:                per-thread statistics
  *                        (atomics, no lock needed)
@@ -504,6 +506,7 @@ struct binder_thread {
 	bool process_todo;
 	struct binder_error return_error;
 	struct binder_error reply_error;
+	struct binder_extended_error ee;
 	wait_queue_head_t wait;
 	struct binder_stats stats;
 	atomic_t tmp_ref;

include/uapi/linux/android/binder.h

@@ -236,6 +236,21 @@ struct binder_frozen_status_info {
 	__u32            async_recv;
 };
 
+/* struct binder_extened_error - extended error information
+ * @id:		identifier for the failed operation
+ * @command:	command as defined by binder_driver_return_protocol
+ * @param:	parameter holding a negative errno value
+ *
+ * Used with BINDER_GET_EXTENDED_ERROR. This extends the error information
+ * returned by the driver upon a failed operation. Userspace can pull this
+ * data to properly handle specific error scenarios.
+ */
+struct binder_extended_error {
+	__u32	id;
+	__u32	command;
+	__s32	param;
+};
+
 #define BINDER_WRITE_READ		_IOWR('b', 1, struct binder_write_read)
 #define BINDER_SET_IDLE_TIMEOUT		_IOW('b', 3, __s64)
 #define BINDER_SET_MAX_THREADS		_IOW('b', 5, __u32)
@@ -249,6 +264,7 @@ struct binder_frozen_status_info {
 #define BINDER_FREEZE			_IOW('b', 14, struct binder_freeze_info)
 #define BINDER_GET_FROZEN_INFO		_IOWR('b', 15, struct binder_frozen_status_info)
 #define BINDER_ENABLE_ONEWAY_SPAM_DETECTION	_IOW('b', 16, __u32)
+#define BINDER_GET_EXTENDED_ERROR	_IOWR('b', 17, struct binder_extended_error)
 
 /*
  * NOTE: Two special error codes you should check for when calling