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    :  // Declares a helper class for use in performing hot-patching operations.
  16    :  // The class takes care of modifying page protections as the patcher works.
  17    :  
  18    :  #ifndef SYZYGY_AGENT_ASAN_SCOPED_PAGE_PROTECTIONS_H_
  19    :  #define SYZYGY_AGENT_ASAN_SCOPED_PAGE_PROTECTIONS_H_
  20    :  
  21    :  #include <windows.h>
  22    :  #include <map>
  23    :  #include "base/callback.h"
  24    :  #include "base/macros.h"
  25    :  
  26    :  namespace agent {
  27    :  namespace asan {
  28    :  
  29    :  // Helper class for managing page protections during hot-patching.
  30    :  // Notice that modifying page protections is inherently racy. This class
  31    :  // performs no locking. It's wise to call this function from under a lock
  32    :  // that prevents concurrent patching on the same module, and the caller must
  33    :  // guarantee that the underlying pages are not unloaded during patching.
  34    :  class ScopedPageProtections {
  35    :   public:
  36    :    // Optional callback for testing. Notifies of pages whose protections have
  37    :    // just been removed.
  38    :    using OnUnprotectCallback = base::Callback<void(void* /* page */,
  39    :                                                    DWORD /* old_prot */)>;
  40    :  
  41  E :    ScopedPageProtections() {}
  42    :    ~ScopedPageProtections();
  43    :  
  44    :    // Makes the page(s) containing @p size bytes starting at @p addr writable.
  45    :    // @param addr The address to be written.
  46    :    // @param size The number of bytes to be written.
  47    :    // @returns true on success, false otherwise.
  48    :    bool EnsureContainingPagesWritable(void* addr, size_t size);
  49    :  
  50    :    // Restores all page protections that have been modified. This is
  51    :    // automatically invoked on destruction. Specifically remembers pages for
  52    :    // which restoring protections failed. Repeated calls to this function
  53    :    // will try again for those pages.
  54    :    // @returns true on success, false otherwise.
  55    :    bool RestorePageProtections();
  56    :  
  57    :    // Allows settings a callback as a testing seam.
  58  E :    void set_on_unprotect(OnUnprotectCallback on_unprotect) {
  59  E :      on_unprotect_ = on_unprotect;
  60  E :    }
  61    :  
  62    :   private:
  63    :    // Helper function for EnsureContainingPagesWritable.
  64    :    // @pre page Points to the beginning of a page.
  65    :    // @param page The address of the page to make writable.
  66    :    bool EnsurePageWritable(void* page);
  67    :  
  68    :    using UnprotectedPages = std::map<void*, DWORD>;
  69    :  
  70    :    // Stores the pages unprotected with their original settings.
  71    :    UnprotectedPages unprotected_pages_;
  72    :  
  73    :    // Optional callback.
  74    :    OnUnprotectCallback on_unprotect_;
  75    :  
  76    :    DISALLOW_COPY_AND_ASSIGN(ScopedPageProtections);
  77    :  };
  78    :  
  79    :  }  // namespace asan
  80    :  }  // namespace agent
  81    :  
  82    :  #endif  // SYZYGY_AGENT_ASAN_SCOPED_PAGE_PROTECTIONS_H_