Trap systems and policies they enable

Trap systems are a type of mechanism used in computer systems to intercept events and take appropriate action. Traps can be implemented at various levels of a system, including the hardware, firmware, and software layers. In the context of security policies, trap systems are often used to enforce access control policies and prevent unauthorized access to sensitive resources.

Kernel trap systems, in particular, are used to intercept system calls made by user-level processes and enforce policies related to access control, resource usage, and other security-related concerns. In this system, the kernel intercepts and examines the system call parameters to ensure that the requested operation is permitted based on the defined security policies. If the operation is permitted, the kernel performs the requested operation and returns control to the calling process. If the operation is not permitted, the kernel returns an error code to the calling process and terminates the system call.

The policies enabled by kernel trap systems can vary depending on the specific implementation and configuration. Some common policies enforced by trap systems include:

1. Access Control: Trap systems can enforce access control policies by restricting access to specific system resources based on user identity, group membership, and other factors. For example, a trap system can prevent unauthorized access to a sensitive file by intercepting file system calls and verifying that the user has the appropriate permissions to access the file.
2. Resource Usage: Trap systems can also be used to enforce policies related to resource usage. For example, a trap system can limit the amount of CPU time or memory that a process is allowed to use to prevent denial-of-service attacks or other resource exhaustion attacks.
3. System Integrity: Trap systems can help enforce policies related to system integrity by detecting and preventing unauthorized modifications to system files, system settings, and other critical components. For example, a trap system can prevent a user from modifying critical system files by intercepting file system calls and verifying that the modification is permitted based on the defined security policies.
4. Logging and Auditing: Trap systems can also be used to generate logs and audit trails of system activity, which can be used for forensic analysis and compliance reporting. For example, a trap system can generate logs of all system calls made by a user-level process, including the parameters passed to each system call and the return value.

The implementation of kernel trap systems can vary depending on the specific operating system and kernel version. Some popular implementations of kernel trap systems include:

1. Linux Security Modules (LSM): LSM is a framework used by the Linux kernel to implement various security policies, including access control, resource usage, and system integrity. LSM enables multiple security modules to be loaded simultaneously and can be customized based on the specific security requirements of the system.
2. TrustedBSD: TrustedBSD is a security-enhanced version of the FreeBSD operating system that includes various security features, including a kernel-level mandatory access control (MAC) framework called TrustedBSD MAC Framework. This framework uses kernel traps to enforce access control policies and prevent unauthorized access to system resources.
3. Solaris Privileges: Solaris Privileges is a security feature of the Solaris operating system that allows fine-grained control over system privileges. Solaris Privileges uses kernel traps to intercept system calls made by user-level processes and enforce policies related to access control, resource usage, and system integrity.

In conclusion, kernel trap systems are a powerful mechanism for enforcing security policies in modern computer systems. By intercepting system calls made by user-level processes, kernel trap systems can enforce policies related to access control, resource usage, system integrity, and logging and auditing. The implementation of kernel trap systems can vary depending on the specific operating system and kernel version, but popular implementations include Linux Security Modules, TrustedBSD, and Solaris Privileges.