my_debugger.py

from ctypes import *
from my_debugger_defines import *

import sys
import time
kernel32 = windll.kernel32

class debugger():

    def __init__(self):
        self.h_process       =     None
        self.pid             =     None
        self.debugger_active =     False
        self.h_thread        =     None
        self.context         =     None
        self.breakpoints     =     {}
        self.first_breakpoint=     True
        self.hardware_breakpoints = {}
        
        # Here let's determine and store 
        # the default page size for the system
        # determine the system page size.
        system_info = SYSTEM_INFO()
        kernel32.GetSystemInfo(byref(system_info))
        self.page_size = system_info.dwPageSize
        
        # TODO: test
        self.guarded_pages      = []
        self.memory_breakpoints = {}
        
    def load(self,path_to_exe):
        
        # dwCreation flag determines how to create the process
        # set creation_flags = CREATE_NEW_CONSOLE if you want
        # to see the calculator GUI
        creation_flags = DEBUG_PROCESS
    
        # instantiate the structs
        startupinfo         = STARTUPINFO()
        process_information = PROCESS_INFORMATION()
        
        # The following two options allow the started process
        # to be shown as a separate window. This also illustrates
        # how different settings in the STARTUPINFO struct can affect
        # the debuggee.
        startupinfo.dwFlags     = 0x1
        startupinfo.wShowWindow = 0x0
        
        # We then initialize the cb variable in the STARTUPINFO struct
        # which is just the size of the struct itself
        startupinfo.cb = sizeof(startupinfo)
        
        if kernel32.CreateProcessA(path_to_exe,
                                   None,
                                   None,
                                   None,
                                   None,
                                   creation_flags,
                                   None,
                                   None,
                                   byref(startupinfo),
                                   byref(process_information)):
            
            print "[*] We have successfully launched the process!"
            print "[*] The Process ID I have is: %d" % \
                         process_information.dwProcessId
            self.pid = process_information.dwProcessId
            self.h_process = self.open_process(self,process_information.dwProcessId)
            self.debugger_active = True
        else:    
            print "[*] Error with error code %d." % kernel32.GetLastError()

    def open_process(self,pid):
        
        # PROCESS_ALL_ACCESS = 0x0x001F0FFF
        h_process = kernel32.OpenProcess(PROCESS_ALL_ACCESS,False,pid) 
        
        return h_process
    
    def attach(self,pid):
        
        self.h_process = self.open_process(pid)
        
        # We attempt to attach to the process
        # if this fails we exit the call
        if kernel32.DebugActiveProcess(pid):
            self.debugger_active = True
            self.pid             = int(pid)
                                  
        else:
            print "[*] Unable to attach to the process."
            
    def run(self):
        
        # Now we have to poll the debuggee for 
        # debugging events           
        while self.debugger_active == True:
            self.get_debug_event() 
    
    def get_debug_event(self):
        
        debug_event    = DEBUG_EVENT()
        continue_status = DBG_CONTINUE
        
        if kernel32.WaitForDebugEvent(byref(debug_event),100):
            # grab various information with regards to the current exception.
            self.h_thread          = self.open_thread(debug_event.dwThreadId)
            self.context           = self.get_thread_context(h_thread=self.h_thread)
            self.debug_event       = debug_event
            
                       
            print "Event Code: %d Thread ID: %d" % \
                (debug_event.dwDebugEventCode,debug_event.dwThreadId)
            
            if debug_event.dwDebugEventCode == EXCEPTION_DEBUG_EVENT:
                self.exception = debug_event.u.Exception.ExceptionRecord.ExceptionCode
                self.exception_address = debug_event.u.Exception.ExceptionRecord.ExceptionAddress
                
                # call the internal handler for the exception event that just occured.
                if self.exception == EXCEPTION_ACCESS_VIOLATION:
                    print "Access Violation Detected."
                elif self.exception == EXCEPTION_BREAKPOINT:
                    continue_status = self.exception_handler_breakpoint()
                elif self.exception == EXCEPTION_GUARD_PAGE:
                    print "Guard Page Access Detected."
                elif self.exception == EXCEPTION_SINGLE_STEP:
                    self.exception_handler_single_step()
                
            kernel32.ContinueDebugEvent(debug_event.dwProcessId, debug_event.dwThreadId, continue_status)

            
    def detach(self):
        
        if kernel32.DebugActiveProcessStop(self.pid):
            print "[*] Finished debugging. Exiting..."
            return True
        else:
            print "There was an error"
            return False
    
    def open_thread (self, thread_id):
        
        h_thread = kernel32.OpenThread(THREAD_ALL_ACCESS, None, thread_id)
        
        if h_thread is not None:
            return h_thread
        else:
            print "[*] Could not obtain a valid thread handle."
            return False
        
    def enumerate_threads(self):
              
        thread_entry     = THREADENTRY32()
        thread_list      = []
        snapshot         = kernel32.CreateToolhelp32Snapshot(TH32CS_SNAPTHREAD, self.pid)
        
        if snapshot is not None:
        
            # You have to set the size of the struct
            # or the call will fail
            thread_entry.dwSize = sizeof(thread_entry)

            success = kernel32.Thread32First(snapshot, byref(thread_entry))

            while success:
                if thread_entry.th32OwnerProcessID == self.pid:
                    thread_list.append(thread_entry.th32ThreadID)
    
                success = kernel32.Thread32Next(snapshot, byref(thread_entry))
            
            # No need to explain this call, it closes handles
            # so that we don't leak them.
            kernel32.CloseHandle(snapshot)
            return thread_list
        else:
            return False
        
    def get_thread_context (self, thread_id=None,h_thread=None):
        
        context = CONTEXT()
        context.ContextFlags = CONTEXT_FULL | CONTEXT_DEBUG_REGISTERS
        
        # Obtain a handle to the thread
        if h_thread is None:
            self.h_thread = self.open_thread(thread_id)
                        
        if kernel32.GetThreadContext(self.h_thread, byref(context)):
            
            return context 
        else:
            return False
    
    def read_process_memory(self,address,length):
        
        data         = ""
        read_buf     = create_string_buffer(length)
        count        = c_ulong(0)
        
        
        kernel32.ReadProcessMemory(self.h_process, address, read_buf, 5, byref(count))
        data    = read_buf.raw
        
        return data
    
    
    def write_process_memory(self,address,data):
        
        count  = c_ulong(0)
        length = len(data)
        
        c_data = c_char_p(data[count.value:])

        if not kernel32.WriteProcessMemory(self.h_process, address, c_data, length, byref(count)):
            return False
        else:
            return True
    
    def bp_set(self,address):
        print "[*] Setting breakpoint at: 0x%08x" % address
        if not self.breakpoints.has_key(address):

            # store the original byte
            old_protect = c_ulong(0)
            kernel32.VirtualProtectEx(self.h_process, address, 1, PAGE_EXECUTE_READWRITE, byref(old_protect))
            
            original_byte = self.read_process_memory(address, 1)
            if original_byte != False:
                
                # write the INT3 opcode
                if self.write_process_memory(address, "\xCC"):
                    
                    # register the breakpoint in our internal list
                    self.breakpoints[address] = (original_byte)
                    return True
            else:
                return False

    
    def exception_handler_breakpoint(self):
        print "[*] Exception address: 0x%08x" % self.exception_address
        # check if the breakpoint is one that we set
        if not self.breakpoints.has_key(self.exception_address):
           
                # if it is the first Windows driven breakpoint
                # then let's just continue on
                if self.first_breakpoint == True:
                   self.first_breakpoint = False
                   print "[*] Hit the first breakpoint."
                   return DBG_CONTINUE
               
        else:
            print "[*] Hit user defined breakpoint."
            # this is where we handle the breakpoints we set 
            # first put the original byte back
            self.write_process_memory(self.exception_address, self.breakpoints[self.exception_address])

            # obtain a fresh context record, reset EIP back to the 
            # original byte and then set the thread's context record
            # with the new EIP value
            self.context = self.get_thread_context(h_thread=self.h_thread)
            self.context.Eip -= 1
            
            kernel32.SetThreadContext(self.h_thread,byref(self.context))
            
            continue_status = DBG_CONTINUE


        return continue_status

    def func_resolve(self,dll,function):
        
        handle  = kernel32.GetModuleHandleA(dll)
        address = kernel32.GetProcAddress(handle, function)
        
        kernel32.CloseHandle(handle)

        return address
    
    def bp_set_hw(self, address, length, condition):
        
        # Check for a valid length value
        if length not in (1, 2, 4):
            return False
        else:
            length -= 1
            
        # Check for a valid condition
        if condition not in (HW_ACCESS, HW_EXECUTE, HW_WRITE):
            return False
        
        # Check for available slots
        if not self.hardware_breakpoints.has_key(0):
            available = 0
        elif not self.hardware_breakpoints.has_key(1):
            available = 1
        elif not self.hardware_breakpoints.has_key(2):
            available = 2
        elif not self.hardware_breakpoints.has_key(3):
            available = 3
        else:
            return False

        # We want to set the debug register in every thread
        for thread_id in self.enumerate_threads():
            context = self.get_thread_context(thread_id=thread_id)

            # Enable the appropriate flag in the DR7
            # register to set the breakpoint
            context.Dr7 |= 1 << (available * 2)

            # Save the address of the breakpoint in the
            # free register that we found
            if   available == 0: context.Dr0 = address
            elif available == 1: context.Dr1 = address
            elif available == 2: context.Dr2 = address
            elif available == 3: context.Dr3 = address

            # Set the breakpoint condition
            context.Dr7 |= condition << ((available * 4) + 16)

            # Set the length
            context.Dr7 |= length << ((available * 4) + 18)

            # Set this threads context with the debug registers
            # set
            h_thread = self.open_thread(thread_id)
            kernel32.SetThreadContext(h_thread,byref(context))

        # update the internal hardware breakpoint array at the used slot index.
        self.hardware_breakpoints[available] = (address,length,condition)

        return True
    
    def exception_handler_single_step(self):
        print "[*] Exception address: 0x%08x" % self.exception_address
        # Comment from PyDbg:
        # determine if this single step event occured in reaction to a hardware breakpoint and grab the hit breakpoint.
        # according to the Intel docs, we should be able to check for the BS flag in Dr6. but it appears that windows
        # isn't properly propogating that flag down to us.
        if self.context.Dr6 & 0x1 and self.hardware_breakpoints.has_key(0):
            slot = 0

        elif self.context.Dr6 & 0x2 and self.hardware_breakpoints.has_key(1):
            slot = 0
        elif self.context.Dr6 & 0x4 and self.hardware_breakpoints.has_key(2):
            slot = 0
        elif self.context.Dr6 & 0x8 and self.hardware_breakpoints.has_key(3):
            slot = 0
        else:
            # This wasn't an INT1 generated by a hw breakpoint
            continue_status = DBG_EXCEPTION_NOT_HANDLED

        # Now let's remove the breakpoint from the list
        if self.bp_del_hw(slot):
            continue_status = DBG_CONTINUE

        print "[*] Hardware breakpoint removed."
        return continue_status
    
    def bp_del_hw(self,slot):
        
        # Disable the breakpoint for all active threads
        for thread_id in self.enumerate_threads():

            context = self.get_thread_context(thread_id=thread_id)
            
            # Reset the flags to remove the breakpoint
            context.Dr7 &= ~(1 << (slot * 2))

            # Zero out the address
            if   slot == 0: 
                context.Dr0 = 0x00000000
            elif slot == 1: 
                context.Dr1 = 0x00000000
            elif slot == 2: 
                context.Dr2 = 0x00000000
            elif slot == 3: 
                context.Dr3 = 0x00000000

            # Remove the condition flag
            context.Dr7 &= ~(3 << ((slot * 4) + 16))

            # Remove the length flag
            context.Dr7 &= ~(3 << ((slot * 4) + 18))

            # Reset the thread's context with the breakpoint removed
            h_thread = self.open_thread(thread_id)
            kernel32.SetThreadContext(h_thread,byref(context))
            
        # remove the breakpoint from the internal list.
        del self.hardware_breakpoints[slot]

        return True

    #TODO: test
    def bp_set_mem (self, address, size):
        
        mbi = MEMORY_BASIC_INFORMATION()
        
        # Attempt to discover the base address of the memory page
        if kernel32.VirtualQueryEx(self.h_process, address, byref(mbi), sizeof(mbi)) < sizeof(mbi):
            return False

    
        current_page = mbi.BaseAddress
    
        # We will set the permissions on all pages that are
        # affected by our memory breakpoint.
        while current_page <= address + size:
        
            # Add the page to the list, this will
            # differentiate our guarded pages from those
            # that were set by the OS or the debuggee process
            self.guarded_pages.append(current_page)
            
            old_protection = c_ulong(0)
            if not kernel32.VirtualProtectEx(self.h_process, current_page, size, mbi.Protect | PAGE_GUARD, byref(old_protection)):
                return False
         
            # Increase our range by the size of the
            # default system memory page size
            current_page += self.page_size
    
        # Add the memory breakpoint to our global list
        self.memory_breakpoints[address] = (address, size, mbi)
    
        return True