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# 1 : : // Copyright (c) 2009-2010 Satoshi Nakamoto # 2 : : // Copyright (c) 2009-2019 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 <support/cleanse.h> # 7 : : # 8 : : #include <cstring> # 9 : : # 10 : : #if defined(_MSC_VER) # 11 : : #include <Windows.h> // For SecureZeroMemory. # 12 : : #endif # 13 : : # 14 : : void memory_cleanse(void *ptr, size_t len) # 15 : 19280384 : { # 16 : : #if defined(_MSC_VER) # 17 : : /* SecureZeroMemory is guaranteed not to be optimized out by MSVC. */ # 18 : : SecureZeroMemory(ptr, len); # 19 : : #else # 20 : 19280384 : std::memset(ptr, 0, len); # 21 : : # 22 : : /* Memory barrier that scares the compiler away from optimizing out the memset. # 23 : : * # 24 : : * Quoting Adam Langley <agl@google.com> in commit ad1907fe73334d6c696c8539646c21b11178f20f # 25 : : * in BoringSSL (ISC License): # 26 : : * As best as we can tell, this is sufficient to break any optimisations that # 27 : : * might try to eliminate "superfluous" memsets. # 28 : : * This method is used in memzero_explicit() the Linux kernel, too. Its advantage is that it # 29 : : * is pretty efficient because the compiler can still implement the memset() efficiently, # 30 : : * just not remove it entirely. See "Dead Store Elimination (Still) Considered Harmful" by # 31 : : * Yang et al. (USENIX Security 2017) for more background. # 32 : : */ # 33 : 19280384 : __asm__ __volatile__("" : : "r"(ptr) : "memory"); # 34 : 19280384 : #endif # 35 : 19280384 : }