Crash Dump Analysis Patterns (Part 292)
Sunday, March 17th, 2024Generative AI LLM models such as GPT-4 are very good at annotation and summarization of disassembly and may provide additional insight (although such insights should be treated with caution):
Summarize:
0: kd> ub fffff804`095c8c5f
WdFilter+0x38c3c:
fffff804`095c8c3c mov rcx,qword ptr [WdFilter+0x16000 (fffff804`095a6000)]
fffff804`095c8c43 mov edx,0Eh
fffff804`095c8c48 mov rcx,qword ptr [rcx+18h]
fffff804`095c8c4c call WdFilter+0x1150 (fffff804`09591150)
fffff804`095c8c51 mov rdi,qword ptr [rbp-39h]
fffff804`095c8c55 xor edx,edx
fffff804`095c8c57 lea ecx,[rdx+1]
fffff804`095c8c5a call WdFilter+0x57198 (fffff804`095e7198)
This sequence of instructions is from the WdFilter module, likely part of the Windows Defender filtering mechanism. The disassembled code provides a glimpse into how certain operations are performed within this module:
Instruction Breakdown:
- The first instruction moves a value from a specific address within the WdFilter module into the rcx register. This address (WdFilter+0×16000) is likely a reference to a data structure or a function pointer used by the filter.
- The mov edx, 0Eh instruction sets the edx register to 14 (in hexadecimal notation, 0Eh), which might be used as an argument for a subsequent function call or an operation code.
- Another value is moved into rcx from the address pointed to by rcx+18h, updating rcx with a new address or value located 24 bytes (18h) from the initial reference. This suggests a traversal or access within a structured data or a chain of function pointers.
- A call is made to another function within the WdFilter module (WdFilter+0×1150), indicating an internal operation or check being performed with the previously set parameters.
- The value at rbp-39h is moved into the rdi register. This instruction likely retrieves a saved value or a pointer from the stack frame for use in subsequent operations.
- The xor edx, edx instruction clears the edx register, setting it to zero. This is a common practice for resetting a register value efficiently.
- The lea ecx,[rdx+1] instruction loads the effective address of edx+1 into ecx, effectively setting ecx to 1. This could be preparing an argument for the next function call.
- Finally, a call is made to another function within the WdFilter module (WdFilter+0×57198), which could be part of the filtering, analysis, or action decision-making process based on the context set by the preceding instructions.
Summary:
This code snippet from the WdFilter module performs a series of data retrieval and setup operations before calling two internal functions. These functions could be involved in processing, analyzing, or taking actions on objects or events within the Windows Defender’s filtering system. The exact purpose of these operations would depend on the broader context of the WdFilter module’s functionality and the data structures it manipulates.
Please also note how instruction annotations are combined, for example, about xor and lea. This Disassembly Summary analysis pattern differs from Annotated Disassembly that is done by a debugger that has access to other parts of memory and meta and symbolic information not available to external text processing tools.
- Dmitry Vostokov @ DumpAnalysis.org + TraceAnalysis.org -