Ensure memsets of sensitive memory aren't optimized away

crypto-openssl.cpp

@@ -30,6 +30,7 @@
 
 #include "crypto.hpp"
 #include "key.hpp"
+#include "util.hpp"
 #include <openssl/aes.h>
 #include <openssl/sha.h>
 #include <openssl/hmac.h>
@@ -61,7 +62,7 @@ Aes_ecb_encryptor::~Aes_ecb_encryptor ()
 	// Note: Explicit destructor necessary because class contains an auto_ptr
 	// which contains an incomplete type when the auto_ptr is declared.
 
-	std::memset(&impl->key, '\0', sizeof(impl->key));
+	explicit_memset(&impl->key, '\0', sizeof(impl->key));
 }
 
 void Aes_ecb_encryptor::encrypt(const unsigned char* plain, unsigned char* cipher)

crypto.cpp

@@ -43,7 +43,7 @@ Aes_ctr_encryptor::Aes_ctr_encryptor (const unsigned char* raw_key, const unsign
 
 Aes_ctr_encryptor::~Aes_ctr_encryptor ()
 {
-	std::memset(pad, '\0', BLOCK_LEN);
+	explicit_memset(pad, '\0', BLOCK_LEN);
 }
 
 void Aes_ctr_encryptor::process (const unsigned char* in, unsigned char* out, size_t len)

key.cpp

@@ -45,8 +45,8 @@
 Key_file::Entry::Entry ()
 {
 	version = 0;
-	std::memset(aes_key, 0, AES_KEY_LEN);
+	explicit_memset(aes_key, 0, AES_KEY_LEN);
-	std::memset(hmac_key, 0, HMAC_KEY_LEN);
+	explicit_memset(hmac_key, 0, HMAC_KEY_LEN);
 }
 
 void		Key_file::Entry::load (std::istream& in)

util.cpp

@@ -81,6 +81,17 @@ void		write_be32 (std::ostream& out, uint32_t i)
 	out.write(reinterpret_cast<const char*>(buffer), 4);
 }
 
+void*		explicit_memset (void* s, int c, std::size_t n)
+{
+	volatile unsigned char* p = reinterpret_cast<unsigned char*>(s);
+
+	while (n--) {
+		*p++ = c;
+	}
+
+	return s;
+}
+
 static void	init_std_streams_platform (); // platform-specific initialization
 
 void		init_std_streams ()

util.hpp

@@ -70,6 +70,7 @@ uint32_t	load_be32 (const unsigned char*);
 void		store_be32 (unsigned char*, uint32_t);
 bool		read_be32 (std::istream& in, uint32_t&);
 void		write_be32 (std::ostream& out, uint32_t);
+void*		explicit_memset (void* s, int c, size_t n);	// memset that won't be optimized away
 void		init_std_streams ();
 mode_t		util_umask (mode_t);
 int		util_rename (const char*, const char*);