Differential D6135 Diff 20261 src/support/cleanse.cpp

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src/support/cleanse.cpp

	// Copyright (c) 2009-2010 Satoshi Nakamoto			// Copyright (c) 2009-2010 Satoshi Nakamoto
	// Copyright (c) 2009-2015 The Bitcoin Core developers			// Copyright (c) 2009-2015 The Bitcoin Core developers
	// Distributed under the MIT software license, see the accompanying			// Distributed under the MIT software license, see the accompanying
	// file COPYING or http://www.opensource.org/licenses/mit-license.php.			// file COPYING or http://www.opensource.org/licenses/mit-license.php.

	#include <support/cleanse.h>			#include <support/cleanse.h>

	#include <openssl/crypto.h>			#include <cstring>

				/**
				* 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 favor 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) {			void memory_cleanse(void *ptr, size_t len) {
	OPENSSL_cleanse(ptr, len);			std::memset(ptr, 0, len);

				/**
				* As best as we can tell, this is sufficient to break any optimizations
				* 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)
				__asm;
				#else
				__asm__ __volatile__("" : : "r"(ptr) : "memory");
				#endif
	}			}