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Software-Based Fault Isolation
What is Software-Based Fault Isolation?
What is Software-Based Fault Isolation? Software-Based Fault Isolation (SFI) is a technique that protects software systems by creating isolated compartments or “sandboxes” (see more on Sandboxing) within a process, restricting untrusted code to a specific memory region and preventing it from accessing or modifying other parts of the system. This method is particularly effective for isolating plug-ins, device drivers, and other untrusted components, minimizing the impact of potential faults on the overall system.
Definition
A method of isolating application modules into distinct fault domains enforced by software. This technique allows untrusted programs written in unsafe languages like C to be executed safely within the single virtual address space of an application. Untrusted machine interpretable code modules are transformed so that all memory accesses are confined to code and data segments within their fault domain. Access to system resources can also be controlled through a unique identifier associated with each domain.
SOURCE: SP 800-19
Key Concepts
- Protection Domains: SFI establishes logical protection domains within a single address space, allowing different modules or components to execute in isolation.
- Sandboxing: Each protected domain is essentially a sandbox, where untrusted code is confined to a specific memory region and its actions are carefully monitored.
- Dynamic Checks: SFI uses dynamic checks before memory access and control transfer instructions to ensure that untrusted code remains within its designated boundary.
- Cross-Domain Communication: While isolated, components in different domains can communicate through a controlled interface, typically using Remote Procedure Calls (RPC).
- Efficiency: SFI is designed to have low overhead, especially when compared to hardware-based isolation which requires frequent context switches.
Benefits
- Security: Isolates untrusted components, reducing the risk of security breaches and system crashes.
- Fault Tolerance: Prevents faults in one component from corrupting other parts of the system.
- Performance: Low overhead, making it suitable for real-time applications and systems with frequent domain crossings.
- Ease of Implementation: Can be implemented with relatively low overhead and minimal changes to existing code.
Applications
- Browsers: Isolating plug-ins to prevent them from compromising the browser.
- Operating Systems: Protecting kernel extensions and device drivers from malicious code.
- Java Virtual Machine (JVM): Isolating native libraries to prevent them from causing system instability.
- Web Servers: Isolating web applications to protect the server from security vulnerabilities.
Limitations
- Not a Silver Bullet: SFI is not a complete security solution and should be used in conjunction with other security measures.
- Overhead: While generally efficient, SFI can introduce some performance overhead, especially when cross-domain communication is frequent.
- Complexity: Implementing and managing SFI can be complex, requiring careful planning and design.
SFI provides a powerful and flexible approach to fault isolation, enabling developers to build more secure, reliable, and efficient software systems.
