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improve SecureWipeBuffer for GCC

pull/2/head
weidai 2009-05-01 22:37:47 +00:00
parent 40c436a7e5
commit 59e1a979cf
1 changed files with 27 additions and 7 deletions
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34
misc.h
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@ -462,7 +462,7 @@ inline void IncrementCounterByOne(byte *output, const byte *input, unsigned int
template <class T> template <class T>
inline void ConditionalSwap(bool c, T &a, T &b) inline void ConditionalSwap(bool c, T &a, T &b)
{ {
T t = (0-T(c)) & (a ^ b); T t = c * (a ^ b);
a ^= t; a ^= t;
b ^= t; b ^= t;
} }
@ -470,8 +470,9 @@ inline void ConditionalSwap(bool c, T &a, T &b)
template <class T> template <class T>
inline void ConditionalSwapPointers(bool c, T &a, T &b) inline void ConditionalSwapPointers(bool c, T &a, T &b)
{ {
CRYPTOPP_COMPILE_ASSERT(sizeof(T) == sizeof(size_t)); ptrdiff_t t = c * (a - b);
ConditionalSwap(c, (size_t &)a, (size_t &)b); a -= t;
b += t;
} }
// see http://www.dwheeler.com/secure-programs/Secure-Programs-HOWTO/protect-secrets.html // see http://www.dwheeler.com/secure-programs/Secure-Programs-HOWTO/protect-secrets.html
@ -479,40 +480,59 @@ inline void ConditionalSwapPointers(bool c, T &a, T &b)
template <class T> template <class T>
void SecureWipeBuffer(T *buf, size_t n) void SecureWipeBuffer(T *buf, size_t n)
{ {
volatile T *p = buf; // GCC 4.3.2 on Cygwin optimizes away the first store if this loop is done in the forward direction
volatile T *p = buf+n;
while (n--) while (n--)
*p++ = 0; *(--p) = 0;
} }
#if defined(_MSC_VER) && _MSC_VER >= 1400 && (CRYPTOPP_BOOL_X64 || CRYPTOPP_BOOL_X86) #if (_MSC_VER >= 1400 || defined(__GNUC__)) && (CRYPTOPP_BOOL_X64 || CRYPTOPP_BOOL_X86)
template<> inline void SecureWipeBuffer(byte *buf, size_t n) template<> inline void SecureWipeBuffer(byte *buf, size_t n)
{ {
volatile byte *p = buf; volatile byte *p = buf;
#ifdef __GNUC__
asm volatile("rep stosb" : "+c"(n), "+D"(p) : "a"(0) : "memory");
#else
__stosb((byte *)(size_t)p, 0, n); __stosb((byte *)(size_t)p, 0, n);
#endif
} }
template<> inline void SecureWipeBuffer(word16 *buf, size_t n) template<> inline void SecureWipeBuffer(word16 *buf, size_t n)
{ {
volatile word16 *p = buf; volatile word16 *p = buf;
#ifdef __GNUC__
asm volatile("rep stosw" : "+c"(n), "+D"(p) : "a"(0) : "memory");
#else
__stosw((word16 *)(size_t)p, 0, n); __stosw((word16 *)(size_t)p, 0, n);
#endif
} }
template<> inline void SecureWipeBuffer(word32 *buf, size_t n) template<> inline void SecureWipeBuffer(word32 *buf, size_t n)
{ {
volatile word32 *p = buf; volatile word32 *p = buf;
#ifdef __GNUC__
asm volatile("rep stosl" : "+c"(n), "+D"(p) : "a"(0) : "memory");
#else
__stosd((unsigned long *)(size_t)p, 0, n); __stosd((unsigned long *)(size_t)p, 0, n);
#endif
} }
template<> inline void SecureWipeBuffer(word64 *buf, size_t n) template<> inline void SecureWipeBuffer(word64 *buf, size_t n)
{ {
#if CRYPTOPP_BOOL_X64 #if CRYPTOPP_BOOL_X64
volatile word64 *p = buf; volatile word64 *p = buf;
#ifdef __GNUC__
asm volatile("rep stosq" : "+c"(n), "+D"(p) : "a"(0) : "memory");
#else
__stosq((word64 *)(size_t)p, 0, n); __stosq((word64 *)(size_t)p, 0, n);
#endif
#else #else
SecureWipeBuffer((word32 *)buf, 2*n); SecureWipeBuffer((word32 *)buf, 2*n);
#endif #endif
} }
#endif
#endif // #if (_MSC_VER >= 1400 || defined(__GNUC__)) && (CRYPTOPP_BOOL_X64 || CRYPTOPP_BOOL_X86)
template <class T> template <class T>
inline void SecureWipeArray(T *buf, size_t n) inline void SecureWipeArray(T *buf, size_t n)