hooklib by capt micro

//hooklib by capt. micro

#ifndef BYTE
typedef unsigned char BYTE;
#endif
#ifndef DWORD
typedef unsigned int DWORD;
#endif
void HookCopy(BYTE *bSrc, BYTE *bDst, DWORD dwSz)
{
    while (--dwSz) *bDst++ = *bSrc++;
}
void HookInstall(DWORD dwInstallAt, DWORD dwInstallSz, DWORD dwDetourFunc)
{
    //Save instructions and generate stub before we overwrite function with the hook
    BYTE *bHookStub = (BYTE*)HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, dwInstallSz + 2 + 5 + 2 + 5);
    HookCopy(bHookStub, (BYTE*)dwInstallAt, dwInstallSz);
    *(bHookStub + dwInstallSz + 0) = 0x60 //pushad \
    *(bHookStub + dwInstallSz + 1) = 0x9C //pushfd  \-----------------------\
    *(bHookStub + dwInstallSz + 2) = 0xE8 //call <users detour function>     |- So we dont utterly fuck the program
    *((DWORD*)(bHookStub + dwInstallSz + 3)) = dwDetourFunc; //             /
    *(bHookStub + dwInstallSz + 7) = 0x9D //popfd   /----------------------/
    *(bHookStub + dwInstallSz + 8) = 0x61 //popad  /
    *(bHookStub + dwInstallSz + 9) = 0xE8 //jmp <dwInstallAt + dwInstallSz> (instruction after hook)
    *((DWORD*)(bHookStub + dwInstallSz + 10)) = dwInstallAt + dwInstallSz;

    //Generate 5 byte hook and install it
    BYTE *bHookInstruction = (BYTE*)dwInstallAt;
    *(bHookInstruction + 0) = 0xE9; //jmp <hook stub>
    *((DWORD*)(bHookInstruction+1)) = bHookStub;

    //Fill the rest with NOPs (not needed really, just nice to have)
    DWORD dwNopFill = dwInstallSz - 5;
    while (dwNopFill > 0)
    {
        *(bHookInstruction + 4 + dwNopFill) = 0x90; //NOP
        dwNopFill--;
    }
}
void HookRemove(DWORD dwInstallAt, DWORD dwInstallSz)
{
    //Get the address of the stub (therefore the saved instructions)
    DWORD dwStubAddr = *((DWORD*)(dwInstallAt + 1));
    BYTE *bHookStub = (BYTE*)dwStubAddr;

    //Copy the saved instructions back to the function
    HookCopy((BYTE*)dwInstallAt, bHookStub, dwInstallSz);

    //Free the stub
    HeapFree(GetProcessHeap(), 0, bHookStub);
}