Difference between revisions of "Process Hook and Read From Memory VB6"

Revision as of 16:27, 3 June 2007

• needs spellchecked

To learn how to hook a running program in Windows we will use calc.exe, the windows calculator, as a guinea pig. So, we create a Visual BASIC program that attaches itself to calc.exe and monitors for the calculator value to change from zero.

Direct Memory Access Class for NT/2000/XP

Already found four key addresses to use for testing with a debugger:

calc.exe+14D55          01014D55
calc.exe+14D56          01014D56
calc.exe+14D57          01014D57
calc.exe+14D58          01014D58

1. Get the Process ID of calc.exe
2. Hook the Process
3. Read the Memory

• Getwindowthreadprocessid: retrieves the identifier of the thread that created the specified window and, optionally, the identifier of the process that created the window.

• ReadProcessMemory: Reads data from an area of memory in a specified process. The entire area to be read must be accessible or the operation fails.

BOOL ReadProcessMemory(
  HANDLE hProcess,
  LPCVOID lpBaseAddress,
  LPVOID lpBuffer,
  SIZE_T nSize,
  SIZE_T* lpNumberOfBytesRead
);

ReadProcessMemory hProcess [in], lpBaseAddress [in], lpBuffer[out], nSize[in], lpNumberOfBytesRead[out]

If the function succeeds, the return value is nonzero. If the function fails, the return value is 0 (zero).

• hProcess: A handle to the process with memory that is being read. The handle must have PROCESS_VM_READ access to the process.
• lpBaseAddress: A pointer to the base address in the specified process from which to read. Before any data transfer occurs, the system verifies that all data in the base address and memory of the specified size is accessible for read access, and if it is not accessible the function fails.
• lpBuffer: A pointer to a buffer that receives the contents from the address space of the specified process.
• nSize: The number of bytes to be read from the specified process.
• lpNumberOfBytesRead: A pointer to a variable that receives the number of bytes transferred into the specified buffer. If lpNumberOfBytesRead is NULL, the parameter is ignored.

ReadProcessMemory Code Snippet

  addr = addr + 1        
  buffer = Space$(1)
  Call ReadProcessMemory(myHandle, addr, buffer, 1, readlen)

• myHandle is a long integer
• addr is a long integer
• buffer is a string variable / buffer = Space$(1) / ???
• readlen is

  myHandle = OpenProcess(&H1F0FFF, False, pid)
  buffer = Space$(1)
  addr = 16798516 ' memory address to what we are watching is
  Call ReadProcessMemory(myHandle, addr, buffer, 1, readlen)