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44 lines
1.5 KiB
C++
44 lines
1.5 KiB
C++
// Copyright (c) 2009-2010 Satoshi Nakamoto
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// Copyright (c) 2009-2017 The Bitcoin Core developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#include <support/cleanse.h>
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#include <cstring>
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#if defined(_MSC_VER)
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#include <Windows.h> // For SecureZeroMemory.
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#endif
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/* Compilers have a bad habit of removing "superfluous" memset calls that
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* are trying to zero memory. For example, when memset()ing a buffer and
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* then free()ing it, the compiler might decide that the memset is
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* unobservable and thus can be removed.
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*
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* Previously we used OpenSSL which tried to stop this by a) implementing
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* memset in assembly on x86 and b) putting the function in its own file
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* for other platforms.
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*
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* This change removes those tricks in favour of using asm directives to
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* scare the compiler away. As best as our compiler folks can tell, this is
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* sufficient and will continue to be so.
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*
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* Adam Langley <agl@google.com>
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* Commit: ad1907fe73334d6c696c8539646c21b11178f20f
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* BoringSSL (LICENSE: ISC)
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*/
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void memory_cleanse(void *ptr, size_t len)
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{
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std::memset(ptr, 0, len);
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/* As best as we can tell, this is sufficient to break any optimisations that
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might try to eliminate "superfluous" memsets. If there's an easy way to
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detect memset_s, it would be better to use that. */
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#if defined(_MSC_VER)
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SecureZeroMemory(ptr, len);
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#else
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__asm__ __volatile__("" : : "r"(ptr) : "memory");
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#endif
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}
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