Various embodiments provide techniques and devices for protecting application secrets from operating system attacks. In some examples, applications execute with an isolated user mode of a secure execution environment, while relying on an operating system executing within a separate execution environment for resource management and system services. A proxy kernel can control access by the operating system to data associated with the secure execution environment. Further, the proxy kernel can act as a transparent interface between isolated user mode applications and the operating system during the provision of resource management and system services.