Pointer Authentication During Speculation for ROP-Resistant Control Flow
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Solution Overview
Problem
ROP attacks compromise system security by modifying return addresses on the stack, allowing attackers to hijack control flow and execute unauthorized code.
Innovation Solution
Implement pointer authentication codes (PACs) using a secret cryptographic key to sign return addresses, authenticating them before use to prevent unauthorized control flow changes, and execute authentication speculatively to avoid processor faults.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pointer authentication is executed synchronously, then control flow integrity is improved, but processor performance deteriorates due to faults during speculative execution
Solution Approach 1:
The patent performs pointer authentication speculatively in advance of the actual control flow transfer. By executing the authentication instruction during speculative execution before the return address is actually used, the system can detect authentication failures early without blocking the normal execution path, thus maintaining both security and performance.
Solution Approach 2:
The patent allows the authentication instruction to be skipped or rushed through during speculative execution when the speculative outcome is known to be safe. By using branch prediction and speculative execution mechanisms, the system can skip authentication steps that are guaranteed to pass, avoiding performance penalties while maintaining security for actual authentication-critical paths.
2Reliability
If return addresses are authenticated before use, then security against ROP attacks is improved, but execution time increases due to authentication overhead
Solution Approach 1:
The patent performs authentication in advance during speculative execution, so that when the return address is actually used, the authentication has already been performed. This preliminary action allows the system to amortize the authentication cost over multiple potential execution paths, reducing the perceived overhead for any single execution path.
Solution Approach 2:
The patent makes the authentication process dynamic by allowing speculative execution to proceed conditionally. When branch prediction indicates a likely correct return address, the system can skip authentication or perform it more lightly. When prediction fails or the path is critical, full authentication is applied. This dynamic approach optimizes the balance between security and performance.
3Productivity
If speculative execution is used for authentication, then performance is improved, but detection of authentication failures becomes more difficult
Solution Approach 1:
The patent implements feedback mechanisms that monitor speculative execution outcomes and authentication results. When speculative execution completes, the system compares the speculative return address with the actual return address and checks authentication status. This feedback loop ensures that authentication failures are detected even when speculative execution was used, as the system can retroactively verify the authenticity of the returned address.
Solution Approach 2:
The patent introduces intermediary structures such as return address stacks and authentication state registers that mediate between speculative execution and actual control flow transfer. These intermediaries preserve authentication information even when speculative execution occurs, allowing the system to detect authentication failures by comparing state in the intermediary structures with expected values after execution completes.
Data Source
AI summary
In an embodiment, a processor includes hardware circuitry which may be used to authenticate instruction operands. The processor may execute instructions that perform operand authentication both speculatively and non-speculatively. During speculative execution of such instructions, the processor may execute authentication such that no differences in observable state of the processor, relative to authentication result, are detectable via a side channel. During speculative execution, a result of authentication may be deferred until speculative execution of the instruction, and additional instructions, may be completed. Upon resolution of a condition that indicates acceptance of the speculative execution, a speculative execution result may cause a processor exception and stalling of execution at the instruction to be performed.