cleanse.cpp raw

   1  // Copyright (c) 2009-2010 Satoshi Nakamoto
   2  // Copyright (c) 2009-present The Bitcoin Core developers
   3  // Distributed under the MIT software license, see the accompanying
   4  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
   5  
   6  #include <support/cleanse.h>
   7  
   8  #include <cstring>
   9  
  10  #if defined(WIN32)
  11  #include <windows.h>
  12  #endif
  13  
  14  void memory_cleanse(void *ptr, size_t len)
  15  {
  16  #if defined(WIN32)
  17      /* SecureZeroMemory is guaranteed not to be optimized out. */
  18      SecureZeroMemory(ptr, len);
  19  #else
  20      std::memset(ptr, 0, len);
  21  
  22      /* Memory barrier that scares the compiler away from optimizing out the memset.
  23       *
  24       * Quoting Adam Langley <agl@google.com> in commit ad1907fe73334d6c696c8539646c21b11178f20f
  25       * in BoringSSL (ISC License):
  26       *    As best as we can tell, this is sufficient to break any optimisations that
  27       *    might try to eliminate "superfluous" memsets.
  28       * This method is used in memzero_explicit() the Linux kernel, too. Its advantage is that it
  29       * is pretty efficient because the compiler can still implement the memset() efficiently,
  30       * just not remove it entirely. See "Dead Store Elimination (Still) Considered Harmful" by
  31       * Yang et al. (USENIX Security 2017) for more background.
  32       */
  33      __asm__ __volatile__("" : : "r"(ptr) : "memory");
  34  #endif
  35  }
  36