Tagged architectures and multi-level UNIX

Tagged architectures are a class of computer architectures where every memory access is checked to ensure that the access is authorized. The idea behind tagged architectures is to provide fine-grained access control to memory, which can help improve security. The UNIX operating system has been modified to work with tagged architectures to create multi-level UNIX, a system that provides strong security guarantees.

Tagged architectures

In a tagged architecture, each memory location has an associated tag that specifies the access privileges of the current process. When a process attempts to access a memory location, the tag is checked to ensure that the access is allowed. If the access is not allowed, an exception is raised and the process is terminated or otherwise handled according to a pre-defined policy. Tagged architectures can provide strong security guarantees because access control is enforced at the hardware level, making it difficult for an attacker to bypass.

Multi-level UNIX

Multi-level UNIX is a modified version of the UNIX operating system that is designed to work with tagged architectures. In multi-level UNIX, each process is assigned a security level, which specifies the process's access privileges. The security level is enforced using the tags associated with each memory location, ensuring that a process cannot access data outside of its security level. The system also includes a mechanism for inter-process communication that enforces security policies to ensure that information is only shared between processes with compatible security levels.

Benefits and challenges

The use of tagged architectures in multi-level UNIX provides several benefits, including strong security guarantees and fine-grained access control to memory. However, there are also several challenges associated with the use of tagged architectures. One challenge is the performance overhead of tag checking, which can be significant. Another challenge is ensuring that the tags associated with each memory location are set correctly and updated as necessary. Finally, there is the challenge of ensuring that applications are designed to work with the security model of multi-level UNIX, which may require modifications to existing applications.

Conclusion

Tagged architectures provide fine-grained access control to memory, which can improve security. Multi-level UNIX is a modified version of the UNIX operating system that works with tagged architectures to provide strong security guarantees. While there are challenges associated with the use of tagged architectures, the benefits make them an attractive option for systems that require strong security guarantees.