Line data    Source code

       1             : // Copyright (c) 2009-2010 Satoshi Nakamoto
       2             : // Copyright (c) 2009-2015 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 "cleanse.h"
       7             : 
       8             : #include <cstring>
       9             : 
      10             : /* Compilers have a bad habit of removing "superfluous" memset calls that
      11             :  * are trying to zero memory. For example, when memset()ing a buffer and
      12             :  * then free()ing it, the compiler might decide that the memset is
      13             :  * unobservable and thus can be removed.
      14             :  *
      15             :  * Previously we used OpenSSL which tried to stop this by a) implementing
      16             :  * memset in assembly on x86 and b) putting the function in its own file
      17             :  * for other platforms.
      18             :  *
      19             :  * This change removes those tricks in favour of using asm directives to
      20             :  * scare the compiler away. As best as our compiler folks can tell, this is
      21             :  * sufficient and will continue to be so.
      22             :  *
      23             :  * Adam Langley <agl@google.com>
      24             :  * Commit: ad1907fe73334d6c696c8539646c21b11178f20f
      25             :  * BoringSSL (LICENSE: ISC)
      26             :  */
      27    31199250 : void memory_cleanse(void *ptr, size_t len)
      28             : {
      29    31199250 :     std::memset(ptr, 0, len);
      30             : 
      31             :     /* As best as we can tell, this is sufficient to break any optimisations that
      32             :        might try to eliminate "superfluous" memsets. If there's an easy way to
      33             :        detect memset_s, it would be better to use that. */
      34             : #if defined(_MSC_VER)
      35             :     __asm;
      36             : #else
      37    31199250 :     __asm__ __volatile__("" : : "r"(ptr) : "memory");
      38             : #endif
      39    31199250 : }