/*
  Inject code into the target process to load our DLL.	The target thread
  should be suspended on entry; it remains suspended on exit.

  Initially I used the "stack" method of injection.  However, this fails
  when DEP is active, since that doesn't allow code to execute in the stack.
  To overcome this I used the "CreateRemoteThread" method.  However, this
  would fail with Wselect, a program to assist batch files.  Wselect runs,
  but it has no output.  As it turns out, removing the suspended flag would
  make Wselect work, but it caused problems with everything else.  So now I
  allocate a section of memory and change the context to run from there.  At
  first I had an event to signal when the library was loaded, then the memory
  was released.  However, that wouldn't work with -p and CMD.EXE (4NT v8
  worked fine).  Since it's possible the DLL might start a process suspended,
  I've decided to simply keep the memory.
*/

#define WIN32_LEAN_AND_MEAN
#include <windows.h>

void InjectDLL64( LPPROCESS_INFORMATION ppi, LPCSTR dll )
{
  CONTEXT context;
  DWORD   len;
  LPVOID  mem;
  DWORD64 LLA;
  #define CODESIZE 92
  static BYTE code[CODESIZE+MAX_PATH] = {
	0,0,0,0,0,0,0,0,	   // original rip
	0,0,0,0,0,0,0,0,	   // LoadLibraryA
	0x9C,			   // pushfq
	0x50,			   // push  rax
	0x51,			   // push  rcx
	0x52,			   // push  rdx
	0x53,			   // push  rbx
	0x55,			   // push  rbp
	0x56,			   // push  rsi
	0x57,			   // push  rdi
	0x41,0x50,		   // push  r8
	0x41,0x51,		   // push  r9
	0x41,0x52,		   // push  r10
	0x41,0x53,		   // push  r11
	0x41,0x54,		   // push  r12
	0x41,0x55,		   // push  r13
	0x41,0x56,		   // push  r14
	0x41,0x57,		   // push  r15
	0x48,0x83,0xEC,0x28,	   // sub   rsp, 40
	0x48,0x8D,0x0D,41,0,0,0,   // lea   ecx, "path\to\ANSI.dll"
	0xFF,0x15,-49,-1,-1,-1,    // call  LoadLibraryA
	0x48,0x83,0xC4,0x28,	   // add   rsp, 40
	0x41,0x5F,		   // pop   r15
	0x41,0x5E,		   // pop   r14
	0x41,0x5D,		   // pop   r13
	0x41,0x5C,		   // pop   r12
	0x41,0x5B,		   // pop   r11
	0x41,0x5A,		   // pop   r10
	0x41,0x59,		   // pop   r9
	0x41,0x58,		   // pop   r8
	0x5F,			   // pop   rdi
	0x5E,			   // pop   rsi
	0x5D,			   // pop   rbp
	0x5B,			   // pop   rbx
	0x5A,			   // pop   rdx
	0x59,			   // pop   rcx
	0x58,			   // pop   rax
	0x9D,			   // popfq
	0xFF,0x25,-91,-1,-1,-1,    // jmp   original Rip
	0,			   // dword alignment for LLA, fwiw
  };

  len = lstrlenA( dll ) + 1;
  if (len > MAX_PATH)
    return;
  CopyMemory( code + CODESIZE, dll, len );
  len += CODESIZE;

  context.ContextFlags = CONTEXT_CONTROL;
  GetThreadContext( ppi->hThread, &context );
  mem = VirtualAllocEx( ppi->hProcess, NULL, len, MEM_COMMIT,
			PAGE_EXECUTE_READWRITE );
  LLA = (DWORD64)GetProcAddress( GetModuleHandleA( "kernel32.dll" ),
						   "LoadLibraryA" );

  union
  {
    PBYTE    pB;
    PDWORD64 pL;
  } ip;
  ip.pB = code;

  *ip.pL++ = context.Rip;
  *ip.pL++ = LLA;

  WriteProcessMemory( ppi->hProcess, mem, code, len, NULL );
  FlushInstructionCache( ppi->hProcess, mem, len );
  context.Rip = (DWORD64)mem + 16;
  SetThreadContext( ppi->hThread, &context );
}