Platform-based workloads: This is a more complex category that covers workloads running on a shared platform that aren't virtual machines or containers, such as logic/procedures running on a shared database platform. Imagine a stored procedure running inside a multitenant database, or a machine- learning job running on a machine-learning Platform as a Service. Isolation and security are totally the responsibility of the platform provider, although the provider may expose certain security options and controls.
Reference: CSA Security GuidelinesV.4(reproduced here for the educational purpose)

Cloud service Provider is responsible for infrastructure in Software as a service(SaaS) service Model

Remember that data security will always remain responsibility of the cloud customer in all service models