1    :  // Copyright 2015 Google Inc. All Rights Reserved.
   2    :  //
   3    :  // Licensed under the Apache License, Version 2.0 (the "License");
   4    :  // you may not use this file except in compliance with the License.
   5    :  // You may obtain a copy of the License at
   6    :  //
   7    :  //     http://www.apache.org/licenses/LICENSE-2.0
   8    :  //
   9    :  // Unless required by applicable law or agreed to in writing, software
  10    :  // distributed under the License is distributed on an "AS IS" BASIS,
  11    :  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  12    :  // See the License for the specific language governing permissions and
  13    :  // limitations under the License.
  14    :  
  15    :  #include "syzygy/kasko/loader_lock.h"
  16    :  
  17    :  #include <stdint.h>
  18    :  #include <winternl.h>
  19    :  
  20    :  namespace kasko {
  21    :  
  22    :  namespace {
  23    :  
  24  E :  void* AddOffset(void* ptr, int offset) {
  25  E :    return reinterpret_cast<uint8_t*>(ptr) + offset;
  26  E :  }
  27    :  
  28    :  }  // namespace
  29    :  
  30  E :  CRITICAL_SECTION* GetLoaderLock() {
  31    :    // The offset to the loader lock in the PEB structure. This value
  32    :    // is undocumented but appears to never change.
  33    :    static const uint32_t kLoaderLockOffset = 0xa0;
  34    :    static_assert(4 == sizeof(void*), "Only supported in 32 bit.");
  35    :    // In 64 bit processes, the offset is 0x110.
  36    :  
  37  E :    PEB* peb = NtCurrentTeb()->ProcessEnvironmentBlock;
  38    :    CRITICAL_SECTION* loader_lock =
  39  E :        *reinterpret_cast<CRITICAL_SECTION**>(AddOffset(peb, kLoaderLockOffset));
  40    :  
  41  E :    return loader_lock;
  42  E :  }
  43    :  
  44    :  }  // namespace kasko