path: root/src/common/memwipe.c

// Copyright (c) 2017, The Monero Project
// 
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// permitted provided that the following conditions are met:
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// 1. Redistributions of source code must retain the above copyright notice, this list of
//    conditions and the following disclaimer.
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// 2. Redistributions in binary form must reproduce the above copyright notice, this list
//    of conditions and the following disclaimer in the documentation and/or other
//    materials provided with the distribution.
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// 3. Neither the name of the copyright holder nor the names of its contributors may be
//    used to endorse or promote products derived from this software without specific
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
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// Parts of this file Copyright (c) 2009-2015 The Bitcoin Core developers

#define __STDC_WANT_LIB_EXT1__ 1
#include <string.h>
#include <stdlib.h>
#ifdef HAVE_EXPLICIT_BZERO
#include <strings.h>
#endif
#include "memwipe.h"

#if defined(_MSC_VER)
#define SCARECROW \
    __asm;
#else
#define SCARECROW \
    __asm__ __volatile__("" : : "r"(ptr) : "memory");
#endif

#ifdef HAVE_MEMSET_S

void *memwipe(void *ptr, size_t n)
{
  if (memset_s(ptr, n, 0, n))
  {
    abort();
  }
  SCARECROW // might as well...
  return ptr;
}

#elif defined HAVE_EXPLICIT_BZERO

void *memwipe(void *ptr, size_t n)
{
  explicit_bzero(ptr, n);
  SCARECROW
  return ptr;
}

#else

/* The memory_cleanse implementation is taken from Bitcoin */

/* Compilers have a bad habit of removing "superfluous" memset calls that
 * are trying to zero memory. For example, when memset()ing a buffer and
 * then free()ing it, the compiler might decide that the memset is
 * unobservable and thus can be removed.
 *
 * Previously we used OpenSSL which tried to stop this by a) implementing
 * memset in assembly on x86 and b) putting the function in its own file
 * for other platforms.
 *
 * This change removes those tricks in favour of using asm directives to
 * scare the compiler away. As best as our compiler folks can tell, this is
 * sufficient and will continue to be so.
 *
 * Adam Langley <agl@google.com>
 * Commit: ad1907fe73334d6c696c8539646c21b11178f20f
 * BoringSSL (LICENSE: ISC)
 */
static void memory_cleanse(void *ptr, size_t len)
{
    memset(ptr, 0, len);

    /* As best as we can tell, this is sufficient to break any optimisations that
       might try to eliminate "superfluous" memsets. If there's an easy way to
       detect memset_s, it would be better to use that. */
    SCARECROW
}

void *memwipe(void *ptr, size_t n)
{
  memory_cleanse(ptr, n);
  SCARECROW
  return ptr;
}

#endif