dynamic-instrumentation

Dynamic Instrumentation Skill

This skill covers dynamic binary instrumentation (DBI), runtime tracing, and program monitoring using LLVM infrastructure.

Dynamic Binary Instrumentation Overview

What is DBI?

Dynamic Binary Instrumentation allows modifying program behavior at runtime without source code access:

• Insert analysis code at arbitrary points
• Monitor program execution
• Modify control flow and data

LLVM-Based DBI Tools

• QBDI: QuarkslaB Dynamic Binary Instrumentation
• Instrew: Fast instrumentation through LLVM lifting
• binopt: Runtime optimization of binary code

QBDI (QuarkslaB DBI)

Basic Usage

#include <QBDI.h>

// Callback function for instrumentation
QBDI::VMAction onInstruction(QBDI::VMInstanceRef vm, 
                              QBDI::GPRState *gprState,
                              QBDI::FPRState *fprState, 
                              void *data) {
    // Get current instruction info
    const QBDI::InstAnalysis *inst = vm.getInstAnalysis();
    
    printf("Executing: 0x%lx - %s %s\n", 
           inst->address, 
           inst->mnemonic, 
           inst->operandsStr);
    
    return QBDI::VMAction::CONTINUE;
}

int main() {
    QBDI::VM vm;
    
    // Get current stack
    uint8_t *fakestack;
    QBDI::allocateVirtualStack(vm.getGPRState(), 0x100000, &fakestack);
    
    // Add instrumentation callback
    vm.addCodeCB(QBDI::PREINST, onInstruction, nullptr);
    
    // Run target function
    QBDI::rword retval;
    vm.call(&retval, (QBDI::rword)targetFunction, {arg1, arg2});
    
    return 0;
}

Memory Access Tracking

QBDI::VMAction onMemoryAccess(QBDI::VMInstanceRef vm,
                               QBDI::GPRState *gprState,
                               QBDI::FPRState *fprState,
                               void *data) {
    // Get memory accesses for current instruction
    std::vector<QBDI::MemoryAccess> memAccesses = vm.getMemoryAccess();
    
    for (const auto &access : memAccesses) {
        const char* type = (access.type == QBDI::MEMORY_READ) ? "READ" : "WRITE";
        printf("%s: addr=0x%lx, size=%d, value=0x%lx\n",
               type, access.accessAddress, access.size, access.value);
    }
    
    return QBDI::VMAction::CONTINUE;
}

// Register callback for memory access events
vm.addMemAccessCB(QBDI::MEMORY_READ_WRITE, onMemoryAccess, nullptr);