mozglue/misc/WindowsStackCookie.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef mozilla_WindowsStackCookie_h
   8 #define mozilla_WindowsStackCookie_h
   9
  10 #if defined(DEBUG) && defined(_M_X64) && !defined(__MINGW64__)
  11
  12 #  include <windows.h>
  13 #  include <winnt.h>
  14
  15 #  include <cstdint>
  16
  17 #  include "mozilla/Types.h"
  18
  19 namespace mozilla {
  20
  21 // This function does pattern matching on the instructions generated for a
  22 // given function, to detect whether it uses stack buffers. More specifically,
  23 // it looks for instructions that characterize the presence of stack cookie
  24 // checks. When this function returns true, it can be a false positive, but we
  25 // use a rather long pattern to make false positives very unlikely.
  26 // Note: Do not use this function inside the function that lives at
  27 //       aFunctionAddress, as that could introduce stack buffers.
  28 // Note: The pattern we use does not work for MinGW builds.
  29 inline bool HasStackCookieCheck(uintptr_t aFunctionAddress) {
  30   DWORD64 imageBase{};
  31   auto entry = ::RtlLookupFunctionEntry(
  32       reinterpret_cast<DWORD64>(aFunctionAddress), &imageBase, nullptr);
  33   if (entry && entry->EndAddress > entry->BeginAddress + 14) {
  34     auto begin = reinterpret_cast<uint8_t*>(imageBase + entry->BeginAddress);
  35     auto end = reinterpret_cast<uint8_t*>(imageBase + entry->EndAddress - 14);
  36     for (auto pc = begin; pc != end; ++pc) {
  37       // 48 8b 05 XX XX XX XX:      mov rax, qword ptr [rip + XXXXXXXX]
  38       if ((pc[0] == 0x48 && pc[1] == 0x8b && pc[2] == 0x05) &&
  39           // 48 31 e0:              xor rax, rsp
  40           (pc[7] == 0x48 && pc[8] == 0x31 && pc[9] == 0xe0) &&
  41           // 48 89 (8|4)4 24 ...:   mov qword ptr [rsp + ...], rax
  42           (pc[10] == 0x48 && pc[11] == 0x89 &&
  43            (pc[12] == 0x44 || pc[12] == 0x84) && pc[13] == 0x24)) {
  44         return true;
  45       }
  46     }
  47   }
  48   // In x64, if there is no entry, then there is no stack allocation, hence
  49   // there is no stack cookie check: "Table-based exception handling requires a
  50   // table entry for all functions that allocate stack space or call another
  51   // function (for example, nonleaf functions)."
  52   // https://learn.microsoft.com/en-us/cpp/build/exception-handling-x64
  53   // Similarly, if the gap between begin and end is less than 14 bytes, then
  54   // the function cannot contain the pattern we are looking for, therefore it
  55   // has no cookie check either.
  56   return false;
  57 }
  58
  59 }  // namespace mozilla
  60
  61 #endif  // defined(DEBUG) && defined(_M_X64) && !defined(__MINGW64__)
  62
  63 #endif  // mozilla_WindowsStackCookie_h