[PATCH v2 07/11] firmware: arm_ffa: Keep framework RX release under lock

[Sudeep Holla]

The framework notification handler drops rx_lock before issuing
FFA_RX_RELEASE, leaving a window where another RX-buffer user can
start a new FF-A transaction before ownership has actually been
returned to firmware.

Move the FFA_RX_RELEASE calls so they execute while rx_lock is still
held on both the kmemdup() failure path and the normal success path.
While doing that, switch the handler to scoped_guard() to keep the
critical section explicit.

Fixes: 285a5ea0f542 ("firmware: arm_ffa: Add support for handling framework notifications")
Signed-off-by: Sudeep Holla <sudeep.holla at kernel.org>
---
 drivers/firmware/arm_ffa/driver.c | 29 +++++++++++++----------------
 1 file changed, 13 insertions(+), 16 deletions(-)

diff --git a/drivers/firmware/arm_ffa/driver.c b/drivers/firmware/arm_ffa/driver.c
index ed502486eb35..18bcbd161805 100644
--- a/drivers/firmware/arm_ffa/driver.c
+++ b/drivers/firmware/arm_ffa/driver.c
@@ -1494,25 +1494,22 @@ static void handle_fwk_notif_callbacks(u32 bitmap)
 	if (!(bitmap & FRAMEWORK_NOTIFY_RX_BUFFER_FULL))
 		return;
 
-	mutex_lock(&drv_info->rx_lock);
+	scoped_guard(mutex, &drv_info->rx_lock) {
+		msg = drv_info->rx_buffer;
+		buf = kmemdup((void *)msg + msg->offset, msg->size, GFP_KERNEL);
+		if (!buf) {
+			ffa_rx_release();
+			return;
+		}
 
-	msg = drv_info->rx_buffer;
-	buf = kmemdup((void *)msg + msg->offset, msg->size, GFP_KERNEL);
-	if (!buf) {
-		mutex_unlock(&drv_info->rx_lock);
-		return;
+		target = SENDER_ID(msg->send_recv_id);
+		if (msg->offset >= sizeof(*msg))
+			uuid_copy(&uuid, &msg->uuid);
+		else
+			uuid_copy(&uuid, &uuid_null);
+		ffa_rx_release();
 	}
 
-	target = SENDER_ID(msg->send_recv_id);
-	if (msg->offset >= sizeof(*msg))
-		uuid_copy(&uuid, &msg->uuid);
-	else
-		uuid_copy(&uuid, &uuid_null);
-
-	mutex_unlock(&drv_info->rx_lock);
-
-	ffa_rx_release();
-
 	read_lock(&drv_info->notify_lock);
 	cb_info = notifier_hnode_get_by_vmid_uuid(notify_id, target, &uuid);
 	read_unlock(&drv_info->notify_lock);

-- 
2.43.0