Line data    Source code

       1              : // Copyright (c) 2009-2010 Satoshi Nakamoto
       2              : // Copyright (c) 2009-2019 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     22964992 : 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     22964992 :     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     22964992 :     __asm__ __volatile__("" : : "r"(ptr) : "memory");
      34              : #endif
      35     22964992 : }