Automatically debug a process from C # code and read register values

Question

I am looking for a way to read the edx registry at a specific address, for example, given in this question: Read eax register

Although my solution should be in C #, and I tried to do this, what I got at the moment is:

public static IntPtr GetEdx(IntPtr address, Process process) { const uint DBG_EXCEPTION_NOT_HANDLED = 0x80010001; const uint EXCEPTION_SINGLE_STEP = 0x80000004; const int DBG_CONTINUE = 0x00010002; // Seems to work better than DBG_EXCEPTION_NOT_HANDLED //DebugSetProcessKillOnExit(0); DEBUG_EVENT evt = new DEBUG_EVENT(); // Attach to the process we provided the thread as an argument if (!DebugActiveProcess(process.Id)) throw new Win32Exception(); CONTEXT context = new CONTEXT(); foreach (ProcessThread thread in process.Threads) { uint iThreadId = (uint)thread.Id; IntPtr hThread = OpenThread( ThreadAccessFlags.SUSPEND_RESUME | ThreadAccessFlags.SET_CONTEXT | ThreadAccessFlags.GET_CONTEXT, false, iThreadId); // Suspent the thread if (SuspendThread(hThread) == -1) throw new ApplicationException("Cannot suspend thread."); context = new CONTEXT { ContextFlags = (uint)CONTEXT_FLAGS.CONTEXT_DEBUG_REGISTERS | (uint)CONTEXT_FLAGS.CONTEXT_INTEGER }; // Get the context if (!GetThreadContext(hThread, ref context)) throw new Win32Exception(); // Change the context context.Dr0 = (uint)address; context.Dr7 = 0x00000001; // Set the changed context back if (!SetThreadContext(hThread, ref context)) throw new Win32Exception(); // Check if setting the context give any errors var error = Marshal.GetLastWin32Error(); if (error != 0) { throw new ApplicationException("Error is setting context."); } // Resume the thread if (ResumeThread(hThread) == -1) throw new ApplicationException("Cannot resume thread."); } while (true) { if (!WaitForDebugEvent(out evt, -1)) throw new Win32Exception(); // Multiple if for easier debugging at this moment if (evt.dwDebugEventCode == (uint)DebugEventType.EXCEPTION_DEBUG_EVENT) { if (evt.Exception.ExceptionRecord.ExceptionCode == EXCEPTION_SINGLE_STEP) { if (evt.Exception.ExceptionRecord.ExceptionAddress == address) { context = new CONTEXT { ContextFlags = (uint)CONTEXT_FLAGS.CONTEXT_DEBUG_REGISTERS | (uint)CONTEXT_FLAGS.CONTEXT_INTEGER }; GetThreadContext((IntPtr)evt.dwThreadId, ref context); return (IntPtr)context.Ebx; // ebx get } } } ContinueDebugEvent(evt.dwProcessId, evt.dwThreadId, DBG_CONTINUE);//DBG_EXCEPTION_NOT_HANDLED); } } 

With a lot of Kernel32 methods:

 [DllImport("kernel32.dll")] static extern int ResumeThread(IntPtr hThread); [DllImport("kernel32.dll")] static extern uint SuspendThread(IntPtr hThread); [DllImport("kernel32.dll")] public static extern IntPtr OpenThread(ThreadAccessFlags dwDesiredAccess, bool bInheritHandle, uint dwThreadId); [DllImport("Kernel32.dll", SetLastError = true)] static extern bool DebugActiveProcess(int dwProcessId); [DllImport("Kernel32.dll", SetLastError = true)] static extern bool WaitForDebugEvent([Out] out DEBUG_EVENT lpDebugEvent, int dwMilliseconds); [DllImport("Kernel32.dll", SetLastError = true)] static extern bool ContinueDebugEvent(int dwProcessId, int dwThreadId, uint dwContinueStatus); [DllImport("Kernel32.dll", SetLastError = true)] public static extern bool IsDebuggerPresent(); [DllImport("kernel32.dll")] private static extern bool GetThreadContext(IntPtr hThread, ref CONTEXT lpContext); [DllImport("kernel32.dll")] public static extern bool SetThreadContext(IntPtr hThread, ref CONTEXT lpContext); [StructLayout(LayoutKind.Sequential)] public unsafe struct DEBUG_EVENT { public readonly uint dwDebugEventCode; public readonly int dwProcessId; public readonly int dwThreadId; [MarshalAs(UnmanagedType.ByValArray, SizeConst = 86, ArraySubType = UnmanagedType.U1)] private readonly byte[] debugInfo; public EXCEPTION_DEBUG_INFO Exception { get { if (debugInfo == null) return new EXCEPTION_DEBUG_INFO(); fixed (byte* ptr = debugInfo) { return *(EXCEPTION_DEBUG_INFO*)ptr; } } } public LOAD_DLL_DEBUG_INFO LoadDll { get { if (debugInfo == null) return new LOAD_DLL_DEBUG_INFO(); fixed (byte* ptr = debugInfo) { return *(LOAD_DLL_DEBUG_INFO*)ptr; } } } } [StructLayout(LayoutKind.Sequential)] public struct LOAD_DLL_DEBUG_INFO { public readonly IntPtr hFile; public readonly IntPtr lpBaseOfDll; public readonly uint dwDebugInfoFileOffset; public readonly uint nDebugInfoSize; public readonly IntPtr lpImageName; public readonly ushort fUnicode; } [StructLayout(LayoutKind.Sequential)] public struct EXCEPTION_DEBUG_INFO { public EXCEPTION_RECORD ExceptionRecord; public readonly uint dwFirstChance; } [StructLayout(LayoutKind.Sequential)] public struct EXCEPTION_RECORD { public readonly uint ExceptionCode; public readonly uint ExceptionFlags; public readonly IntPtr ExceptionRecord; public readonly IntPtr ExceptionAddress; public readonly uint NumberParameters; //[MarshalAs(UnmanagedType.ByValArray, SizeConst = 15, ArraySubType = UnmanagedType.U4)] //public readonly uint[] ExceptionInformation; public unsafe fixed uint ExceptionInformation[15]; } public enum DebugEventType : int { CREATE_PROCESS_DEBUG_EVENT = 3, //Reports a create-process debugging event. The value of u.CreateProcessInfo specifies a CREATE_PROCESS_DEBUG_INFO structure. CREATE_THREAD_DEBUG_EVENT = 2, //Reports a create-thread debugging event. The value of u.CreateThread specifies a CREATE_THREAD_DEBUG_INFO structure. EXCEPTION_DEBUG_EVENT = 1, //Reports an exception debugging event. The value of u.Exception specifies an EXCEPTION_DEBUG_INFO structure. EXIT_PROCESS_DEBUG_EVENT = 5, //Reports an exit-process debugging event. The value of u.ExitProcess specifies an EXIT_PROCESS_DEBUG_INFO structure. EXIT_THREAD_DEBUG_EVENT = 4, //Reports an exit-thread debugging event. The value of u.ExitThread specifies an EXIT_THREAD_DEBUG_INFO structure. LOAD_DLL_DEBUG_EVENT = 6, //Reports a load-dynamic-link-library (DLL) debugging event. The value of u.LoadDll specifies a LOAD_DLL_DEBUG_INFO structure. OUTPUT_DEBUG_STRING_EVENT = 8, //Reports an output-debugging-string debugging event. The value of u.DebugString specifies an OUTPUT_DEBUG_STRING_INFO structure. RIP_EVENT = 9, //Reports a RIP-debugging event (system debugging error). The value of u.RipInfo specifies a RIP_INFO structure. UNLOAD_DLL_DEBUG_EVENT = 7, //Reports an unload-DLL debugging event. The value of u.UnloadDll specifies an UNLOAD_DLL_DEBUG_INFO structure. } [StructLayout(LayoutKind.Sequential)] public struct CONTEXT { public uint ContextFlags; public uint Dr0; public uint Dr1; public uint Dr2; public uint Dr3; public uint Dr6; public uint Dr7; public FLOATING_SAVE_AREA FloatSave; public uint SegGs; public uint SegFs; public uint SegEs; public uint SegDs; public uint Edi; public uint Esi; public uint Ebx; public uint Edx; public uint Ecx; public uint Eax; public uint Ebp; public uint Eip; public uint SegCs; public uint EFlags; public uint Esp; public uint SegSs; [MarshalAs(UnmanagedType.ByValArray, SizeConst = 512)] public byte[] ExtendedRegisters; } public enum CONTEXT_FLAGS : uint { CONTEXT_i386 = 0x10000, CONTEXT_i486 = 0x10000, CONTEXT_CONTROL = CONTEXT_i386 | 0x01, CONTEXT_INTEGER = CONTEXT_i386 | 0x02, CONTEXT_SEGMENTS = CONTEXT_i386 | 0x04, CONTEXT_FLOATING_POINT = CONTEXT_i386 | 0x08, CONTEXT_DEBUG_REGISTERS = CONTEXT_i386 | 0x10, CONTEXT_EXTENDED_REGISTERS = CONTEXT_i386 | 0x20, CONTEXT_FULL = CONTEXT_CONTROL | CONTEXT_INTEGER | CONTEXT_SEGMENTS, CONTEXT_ALL = CONTEXT_CONTROL | CONTEXT_INTEGER | CONTEXT_SEGMENTS | CONTEXT_FLOATING_POINT | CONTEXT_DEBUG_REGISTERS | CONTEXT_EXTENDED_REGISTERS } [Flags] public enum ThreadAccessFlags : int { TERMINATE = 0x0001, SUSPEND_RESUME = 0x0002, GET_CONTEXT = 0x0008, SET_CONTEXT = 0x0010, SET_INFORMATION = 0x0020, QUERY_INFORMATION = 0x0040, SET_THREAD_TOKEN = 0x0080, IMPERSONATE = 0x0100, DIRECT_IMPERSONATION = 0x0200 } [StructLayout(LayoutKind.Sequential)] public struct FLOATING_SAVE_AREA { public uint ControlWord; public uint StatusWord; public uint TagWord; public uint ErrorOffset; public uint ErrorSelector; public uint DataOffset; public uint DataSelector; // missing some stuff public uint Cr0NpxState; } [DllImport("kernel32.dll")] private static extern int VirtualQueryEx(IntPtr hProcess, IntPtr lpAddress, out MEMORY_BASIC_INFORMATION lpBuffer, int dwLength); [DllImport("kernel32.dll")] public static extern bool ReadProcessMemory(IntPtr hProcess, int lpBaseAddress, byte[] buffer, int size, int lpNumberOfBytesRead); 

But for some reason it never gets into evt.Exception.ExceptionRecord.ExceptionAddress == address

I am new to reading memory and have difficulty figuring out what is wrong with the code above.

EDIT: Also, if I uncomment context.Dr7 = 0x00000001; The application I'm trying to read is crashing.

Answer 1

Theory :

You want to connect to the process, place a breakpoint in it, register the event in the debugger application and wait for this event. You need to put a breakpoint on the address that you specify as a parameter, and after reading the context, you can see the contents of the EDX. This seems reasonable, as a human developer would do.

Implementation:

Looking at your implementation, the method you are trying to use to place a breakpoint at an address seems suspicious. Reading here I understand that trying to establish a context in the current thread can give unpredictable results. You may also not have sufficient permissions. Assuming you have permissions, try stopping the threads before setting up the context .

Another problem that I predict is that the thread you want to stop and debug has a context that needs to be changed as little as possible . I think you should first stop the stream, read its context, change the Dr0 flag (assuming that where you set the breakpoint), and then set the context with all the other register information unchanged.

Without this, I think that you basically change the execution of the program, and I have a strong feeling that some of these registers are read-only.

These are 2 things you need to consider. Hope this helps.

Debugging:

If this does not work, you need to add a function that uses GetLastError () to understand why the functions fail (I suspect that SetThreadContext () will be causing problems in the first place).

You must also ensure that the context structure is defined correctly and that all members have the same order as defined here . The structure must be aligned with C # code just like in unmanaged code.

Also check if you are running on a 64-bit OS. The thread context in a 64-bit OS is different from the context of a 32-bit one. Registers are extended for 64b and so on. If you use a 64-bit OS, you must redefine the context structure . The same thing happens if you use an ARM machine.

Answer 2

Your answer seems to be hiding in one of the comments that you transplant with other code ... Functions for setting and getting the context of the thread require access to the thread (it may be opened using OpenThread using the appropriate permissions, including at least / set context). Instead, you obviously pass in the cast id of the process. You should consider checking the return value for success, probably this would help identify your problem.