1 files changed, 34 insertions, 4 deletions
diff --git a/src/support/cleanse.cpp b/src/support/cleanse.cpp
index a2141b2449..9bf7eda785 100644
--- a/src/support/cleanse.cpp
+++ b/src/support/cleanse.cpp
@@ -1,13 +1,43 @@
 // Copyright (c) 2009-2010 Satoshi Nakamoto
-// Copyright (c) 2009-2015 The Bitcoin Core developers
+// Copyright (c) 2009-2017 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 "cleanse.h"
+#include <support/cleanse.h>
 
-#include <openssl/crypto.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)
 {
-    OPENSSL_cleanse(ptr, 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
 }