Platform.sh provides a Platform as a Service (PaaS) solution and has many customers that require us to maintain various cloud compliance certifications (e.g. to be SOC2 compliant). These certifications contain requirements to ensure certain measures are implemented to meet industry standards. Some requirements are the responsibility of the host, some are the responsibility of the application developer, and others are a shared responsibility.
To know more about security, compliance guidance and shared responsibilities, you can check this information in Platform.sh web page.
If you need any more specific document or information, don't hesitate to open a support ticket.