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// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2018 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#include <support/cleanse.h>
#include <cstring>
#if defined(_MSC_VER)
#include <Windows.h> // For SecureZeroMemory.
#endif
/* 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)
*/
void memory_cleanse(void *ptr, size_t len)
{
std::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. */
#if defined(_MSC_VER)
SecureZeroMemory(ptr, len);
#else
__asm__ __volatile__("" : : "r"(ptr) : "memory");
#endif
}
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