firmware: arm_ffa: Check xa_load() return value

Add a check to verify the result of xa_load() during the partition
lookups done while registering/unregistering the scheduler receiver
interrupt callbacks and while executing the main scheduler receiver
interrupt callback handler.

Fixes: 0184450b ("firmware: arm_ffa: Add schedule receiver callback mechanism")
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Link: https://lore.kernel.org/r/20240108-ffa_fixes_6-8-v1-3-75bf7035bc50@arm.comSigned-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/arm_ffa/driver.c

@@ -733,6 +733,11 @@ static void __do_sched_recv_cb(u16 part_id, u16 vcpu, bool is_per_vcpu)
 	void *cb_data;
 
 	partition = xa_load(&drv_info->partition_info, part_id);
+	if (!partition) {
+		pr_err("%s: Invalid partition ID 0x%x\n", __func__, part_id);
+		return;
+	}
+
 	read_lock(&partition->rw_lock);
 	callback = partition->callback;
 	cb_data = partition->cb_data;
@@ -915,6 +920,11 @@ static int ffa_sched_recv_cb_update(u16 part_id, ffa_sched_recv_cb callback,
 		return -EOPNOTSUPP;
 
 	partition = xa_load(&drv_info->partition_info, part_id);
+	if (!partition) {
+		pr_err("%s: Invalid partition ID 0x%x\n", __func__, part_id);
+		return -EINVAL;
+	}
+
 	write_lock(&partition->rw_lock);
 
 	cb_valid = !!partition->callback;