// Copyright 2010-2014, Google Inc.
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#include "base/win_api_test_helper.h"

#include <Windows.h>
#include <winnt.h>

#include <type_traits>
#include <map>
#include <memory>
#include <vector>

#include "base/util.h"

namespace mozc {
namespace {
using std::unique_ptr;
typedef WinAPITestHelper::FunctionPointer FunctionPointer;

void WINAPI dummy_func() {}
static_assert(sizeof(&dummy_func) == sizeof(FunctionPointer),
              "check function pointer size failed.");

struct Thunk {
  FunctionPointer proc;
};

class ThunkRewriter {
 public:
  ThunkRewriter(const Thunk *thunk, FunctionPointer proc)
      : thunk_(thunk),
        proc_(proc) {}

  bool Rewrite() const {
    // Note: There is a race condition between the first VirtualProtect and
    // second VirtualProtect.

    auto *writable_thunk = const_cast<Thunk *>(thunk_);

    DWORD original_protect = 0;
    auto result = ::VirtualProtect(
        writable_thunk, sizeof(*writable_thunk), PAGE_READWRITE,
        &original_protect);
    if (result == 0) {
      const auto error = ::GetLastError();
      LOG(FATAL) << "VirtualProtect failed. error = " << error;
      return false;
    }

    // Here we have write access to the |writable_thunk|.
    writable_thunk->proc = proc_;

    DWORD dummy = 0;
    result = ::VirtualProtect(
        writable_thunk, sizeof(*writable_thunk), original_protect, &dummy);
    if (result == 0) {
      const auto error = ::GetLastError();
      LOG(FATAL) << "VirtualProtect failed. error = " << error;
      return false;
    }
    return true;
  }

 private:
  // Represents the memory address of API thunk.
  const Thunk *thunk_;
  // Represents the true address of API implementation.
  FunctionPointer proc_;
};

class HookTargetInfo {
 public:
  explicit HookTargetInfo(
      const vector<WinAPITestHelper::HookRequest> &requests) {
    for (size_t i = 0; i < requests.size(); ++i) {
      const auto &request = requests[i];
      HMODULE module_handle = nullptr;
      const auto result = ::GetModuleHandleExA(
          GET_MODULE_HANDLE_EX_FLAG_PIN, request.module_name.c_str(),
          &module_handle);
      if (result == 0) {
        const auto error = ::GetLastError();
        LOG(FATAL) << "GetModuleHandleExA failed. error = " << error;
        continue;
      }
      const FunctionPointer original_proc_address =
          ::GetProcAddress(module_handle, request.proc_name.c_str());
      if (original_proc_address == nullptr) {
        LOG(FATAL) << "GetProcAddress returned nullptr.";
        continue;
      }

      string module_name = request.module_name;
      Util::LowerString(&module_name);
      info_[module_name][original_proc_address] = request.new_proc_address;
    }
  }

  const bool IsTargetModule(const string &module_name) const {
    string lower_module_name(module_name);
    Util::LowerString(&lower_module_name);
    return info_.find(lower_module_name) != info_.end();
  }

  const FunctionPointer GetNewProc(
      const string &module_name,
      FunctionPointer original_proc) const {
    string lower_module_name(module_name);
    Util::LowerString(&lower_module_name);
    const auto module_iterator = info_.find(lower_module_name);
    if (module_iterator == info_.end()) {
      return nullptr;
    }
    const auto &proc_map = module_iterator->second;
    const auto proc_iterator = proc_map.find(original_proc);
    if (proc_iterator == proc_map.end()) {
      return nullptr;
    }
    return proc_iterator->second;
  }

 private:
  map<string, map<FunctionPointer, FunctionPointer>> info_;
};

class PortableExecutableImage {
 public:
  explicit PortableExecutableImage(HMODULE module_handle)
      : module_handle_(module_handle),
        is_invalid_image_(false) {
    if (module_handle_ == nullptr) {
      is_invalid_image_ = true;
      return;
    }
    const auto *dos_header = At<IMAGE_DOS_HEADER>(0);
    if (dos_header->e_magic != IMAGE_DOS_SIGNATURE) {
      is_invalid_image_ = true;
      return;
    }
    const auto *nt_header = At<IMAGE_NT_HEADERS>(dos_header->e_lfanew);
    if (nt_header->Signature != IMAGE_NT_SIGNATURE) {
      is_invalid_image_ = true;
      return;
    }
  }

  template <typename T>
  const T *At(DWORD offset) const {
    static_assert(std::is_pod<T>::value, "T should be POD.");

    CHECK(!is_invalid_image_);

    // TODO(yukawa): Validate if this memory range is safe to be accessed.
    return reinterpret_cast<const T *>(
        reinterpret_cast<const uint8 *>(module_handle_) + offset);
  }

  bool IsValid() const {
    return !is_invalid_image_;
  }

 private:
  HMODULE module_handle_;
  bool is_invalid_image_;
};

class ImageImportDescriptorIterator {
 public:
  explicit ImageImportDescriptorIterator(const PortableExecutableImage &image)
      : image_(image),
        import_directory_(nullptr),
        descriptor_index_(0),
        descriptor_index_max_(0) {
    if (!image_.IsValid()) {
      return;
    }
    const auto *dos_header = image_.At<IMAGE_DOS_HEADER>(0);
    const auto *nt_header = image_.At<IMAGE_NT_HEADERS>(dos_header->e_lfanew);
    import_directory_ =
        &nt_header->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT];
    descriptor_index_max_ =
        import_directory_->Size / sizeof(IMAGE_IMPORT_DESCRIPTOR);
  }

  const IMAGE_IMPORT_DESCRIPTOR &Get() const {
    const auto *desc = GetInternal();
    CHECK_NE(0, desc->Name);
    return *desc;
  }

  void Next() {
    ++descriptor_index_;
  }

  bool Done() const {
    if (!image_.IsValid()) {
      return true;
    }
    if (descriptor_index_ >= descriptor_index_max_) {
      return true;
    }
    if (GetInternal()->Name == 0) {
      return true;
    }
    return false;
  }

 private:
  const IMAGE_IMPORT_DESCRIPTOR *GetInternal() const {
    CHECK_LT(descriptor_index_, descriptor_index_max_);
    const DWORD import_descriptor_offset =
        import_directory_->VirtualAddress +
        descriptor_index_ * sizeof(IMAGE_IMPORT_DESCRIPTOR);
    return image_.At<IMAGE_IMPORT_DESCRIPTOR>(import_descriptor_offset);
  }

  const PortableExecutableImage &image_;
  const IMAGE_DATA_DIRECTORY *import_directory_;
  size_t descriptor_index_;
  size_t descriptor_index_max_;
};

class ImageThunkDataIterator {
 public:
  ImageThunkDataIterator(const PortableExecutableImage &image,
                         const IMAGE_IMPORT_DESCRIPTOR &import_descriptor)
      : image_(image),
        import_descriptor_(import_descriptor),
        thunk_index_(0) {}

  const Thunk *Get() const {
    CHECK(!Done());
    const auto *raw_thunk = GetInternal();
    return reinterpret_cast<const Thunk *>(&raw_thunk->u1.Function);
  }

  void Next() {
    ++thunk_index_;
  }

  bool Done() const {
    return GetInternal()->u1.Function == 0;
  }

 private:
  const IMAGE_THUNK_DATA *GetInternal() const {
    const DWORD thunk_offset =
        import_descriptor_.FirstThunk + thunk_index_ * sizeof(IMAGE_THUNK_DATA);
    return image_.At<IMAGE_THUNK_DATA>(thunk_offset);
  }

  const PortableExecutableImage &image_;
  const IMAGE_IMPORT_DESCRIPTOR &import_descriptor_;
  size_t thunk_index_;
};

}  // namespace

class WinAPITestHelper::RestoreInfo {
 public:
  vector<ThunkRewriter> rewrites;
};

WinAPITestHelper::HookRequest::HookRequest(
    const string &src_module,
    const string &src_proc_name,
    FunctionPointer new_proc_addr)
    : module_name(src_module),
      proc_name(src_proc_name),
      new_proc_address(new_proc_addr) {}

// static
WinAPITestHelper::RestoreInfoHandle WinAPITestHelper::DoHook(
    HMODULE target_module,
    const vector<WinAPITestHelper::HookRequest> &requests) {
  const HookTargetInfo target_info(requests);

  // Following code skips some data validations as this code is only used in
  // unit tests.

  PortableExecutableImage image(target_module);
  CHECK(image.IsValid());

  unique_ptr<RestoreInfo> restore_info(new RestoreInfo());
  for (ImageImportDescriptorIterator descriptor_iterator(image);
       !descriptor_iterator.Done(); descriptor_iterator.Next()) {
    const auto &descriptor = descriptor_iterator.Get();
    const string module_name(image.At<char>(descriptor.Name));
    if (!target_info.IsTargetModule(module_name)) {
      continue;
    }
    for (ImageThunkDataIterator thunk_iterator(image, descriptor);
         !thunk_iterator.Done(); thunk_iterator.Next()) {
      const auto *thunk = thunk_iterator.Get();
      const auto original_proc_address = thunk->proc;
      const auto target_proc_address =
          target_info.GetNewProc(module_name, original_proc_address);
      if (target_proc_address == nullptr) {
        continue;
      }
      // Rewrite rule to do hook.
      ThunkRewriter hook_rewriter(thunk, target_proc_address);
      // Rewrite rule to restore hook.
      ThunkRewriter backup_rewriter(thunk, original_proc_address);
      CHECK(hook_rewriter.Rewrite());
      restore_info->rewrites.push_back(backup_rewriter);
    }
  }
  return restore_info.release();
}

void WinAPITestHelper::RestoreHook(
    WinAPITestHelper::RestoreInfoHandle restore_info) {
  unique_ptr<RestoreInfo> info(restore_info);  // takes ownership

  for (size_t i = 0; i < info->rewrites.size(); ++i) {
    const auto &rewrite = info->rewrites[i];
    CHECK(rewrite.Rewrite());
  }
}

}  // namespace mozc