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(_MSC_VER)
      11             : #include <Windows.h> // For SecureZeroMemory.
      12             : #endif
      13             : 
      14    12860555 : void memory_cleanse(void *ptr, size_t len)
      15             : {
      16             : #if defined(_MSC_VER)
      17             :     /* SecureZeroMemory is guaranteed not to be optimized out by MSVC. */
      18             :     SecureZeroMemory(ptr, len);
      19             : #else
      20    12860555 :     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    12860555 :     __asm__ __volatile__("" : : "r"(ptr) : "memory");
      34             : #endif
      35    12860555 : }