Software Fault Isolation (SFI) in a Nutshell:
Goal and Solution:
- Problem: Unsafe languages like C lack built-in memory safety, making programs susceptible to runtime errors and security vulnerabilities.
- Solution: SFI provides a runtime safeguard by transforming programs, especially those from untrusted sources, to confine their memory access within a secure area, or “sandbox.”
SFI Approach:
Transformation at Binary Level: SFI transforms the program at the binary level by adding code sequences to enforce memory boundaries.
Post-transformation Verification: After transformation, a trusted SFI verifier ensures the code’s compliance with safety constraints.
Simplicity for Verification: Since the verifier assumes the code has undergone SFI, it remains simple, reducing both verification time and the Trusted Computing Base.
Proof Carrying Code Concept: This is akin to Proof Carrying Code, where an untrusted compiler generates code, and a trusted or verified binary verifier ensures adherence to safety measures.
Suitability for Untrusted Code: Traditional SFI is particularly effective for executing binary code from untrusted sources, adding a layer of security to potentially risky software.