Enforcement

Tetragon allows enforcing events in the kernel inline with the operation itself. This document describes the types of enforcement provided by Tetragon and concerns policy implementors must be aware of.

There are two ways that Tetragon performs enforcement: overriding the return value of a function and sending a signal (e.g., SIGKILL) to the process.

Override return value

Override the return value of a call means that the function will never be executed and, instead, a value (typically an error) will be returned to the caller. Generally speaking, only system calls and security check functions allow to change their return value in this manner. Details about how users can configure tracing policies to override the return value can be found in the Override action documentation.

Signals

Another type of enforcement is signals. For example, users can write a TracingPolicy (details can be found in the Signal action documentation) that sends a SIGKILL to a process matching certain criteria and thus terminate it.

In contrast with overriding the return value, sending a SIGKILL signal does not always stop the operation being performed by the process that triggered the operation. For example, a SIGKILL sent in a write() system call does not guarantee that the data will not be written to the file. However, it does ensure that the process is terminated synchronously (and any threads will be stopped). In some cases it may be sufficient to ensure the process is stopped and the process does not handle the return of the call. To ensure the operation is not completed, though, the Signal action should be combined with the Override action.