Test Executive Guard Bits for Buffer Overwrite Detection
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Solution Overview
Problem
Test executive sequences face difficulties in detecting and preventing errors caused by user-supplied code modules that write outside the bounds of buffer parameters, leading to intermittent and hard-to-reproduce issues known as 'Heisenbugs', which can corrupt heap data and mislead users into thinking the problem lies with the vendor's software.
Innovation Solution
The implementation of guard bits in the test executive engine to detect and prevent buffer overwriting by user-supplied code modules, where guard bits are allocated in memory blocks for buffer parameters, and their initial values are checked after module execution to identify any changes, thereby reporting errors and preventing data corruption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If user-supplied code modules are allowed to execute without buffer bounds checking, then ease of operation and programming flexibility are improved, but reliability deteriorates due to buffer overwriting errors and heap data corruption
Solution Approach 1:
The patent applies preliminary action by allocating guard bits in the memory block before passing the buffer to the user-supplied code module. These guard bits are positioned at the boundaries of the buffer and serve as early warning indicators. If the module writes outside buffer bounds, it will overwrite the guard bits, providing immediate detection of the error condition before heap data corruption occurs.
Solution Approach 2:
The patent uses guard bits as an intermediary element between the buffer and the surrounding heap data. These intermediary bits act as a protective layer that absorbs or detects unauthorized writes. By placing undetectable or specially-marked guard bits at buffer boundaries, the system creates a mediator that can identify buffer overruns without requiring the user code to implement its own bounds checking.
2Reliability
If guard bits are allocated and checked for every buffer parameter, then reliability is improved by detecting buffer overwriting, but device complexity increases due to additional memory allocation and verification operations
Solution Approach 1:
The patent merges the buffer allocation process with the guard bit allocation process. Instead of separately allocating buffers and then adding protection, the guard bits are allocated as part of the same memory management operation that allocates the buffer itself. This integration occurs within the test executive engine's existing memory allocation routines, combining multiple functions into a unified process.
Solution Approach 2:
The system applies self-service by automatically allocating and managing guard bits without requiring user intervention. The test executive engine autonomously inserts guard bits into memory blocks, tracks their locations, and checks them after module execution. This automated approach eliminates the need for users to manually manage buffer boundaries or implement their own protection mechanisms.
3Manufacturing precision
If comprehensive error detection is implemented through guard bits, then manufacturing precision is improved by detecting buffer boundary violations, but loss of time occurs due to additional checking operations and error reporting overhead
Solution Approach 1:
The patent applies partial action by checking only the guard bits at buffer boundaries rather than verifying every memory access within the buffer. This selective checking approach provides sufficient error detection capability while minimizing the overhead compared to comprehensive bounds checking on every operation. The guard bits offer a lightweight verification mechanism that checks only what is necessary to detect overruns.
Data Source
AI summary
A test executive sequence may be created by including a plurality of test executive steps in the test executive sequence and configuring at least a subset of the steps to call user-supplied code modules. One or more of the user-supplied code modules may take buffer parameters. The test executive sequence may be executed on a host computer under control of a test executive engine. When executing each step in the test executive sequence that calls a user-supplied code module that takes a buffer parameter, the test executive engine may be operable to perform several operations related to detecting a situation where the user-supplied code module writes outside the bounds of the buffer parameter and/or preventing the user-supplied code module from corrupting heap data if the user-supplied code module writes outside the bounds of the buffer parameter.