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Call a weak function in sodium_memcmp() to prevent LTO.

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sodium_memcmp() can be used to compare user-provided secrets against
constant, hardcoded secrets. We don't want the compiler to generate code
that would be optimized for these hardcoded values.
This commit is contained in:
Frank Denis 2015-09-09 09:33:20 +02:00
parent 0f1f8a6ea6
commit e424963ae8
1 changed files with 22 additions and 2 deletions
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24
src/libsodium/sodium/utils.c
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@ -51,7 +51,7 @@ static unsigned char canary[CANARY_SIZE];
#ifdef HAVE_WEAK_SYMBOLS #ifdef HAVE_WEAK_SYMBOLS
__attribute__((weak)) void __attribute__((weak)) void
_sodium_dummy_symbol_to_prevent_lto(void * const pnt, const size_t len) _sodium_dummy_symbol_to_prevent_memzero_lto(void * const pnt, const size_t len)
{ {
(void) pnt; (void) pnt;
(void) len; (void) len;
@ -71,7 +71,7 @@ sodium_memzero(void * const pnt, const size_t len)
explicit_bzero(pnt, len); explicit_bzero(pnt, len);
#elif HAVE_WEAK_SYMBOLS #elif HAVE_WEAK_SYMBOLS
memset(pnt, 0, len); memset(pnt, 0, len);
_sodium_dummy_symbol_to_prevent_lto(pnt, len); _sodium_dummy_symbol_to_prevent_memzero_lto(pnt, len);
#else #else
volatile unsigned char *pnt_ = (volatile unsigned char *) pnt; volatile unsigned char *pnt_ = (volatile unsigned char *) pnt;
size_t i = (size_t) 0U; size_t i = (size_t) 0U;
@ -82,14 +82,34 @@ sodium_memzero(void * const pnt, const size_t len)
#endif #endif
} }
#ifdef HAVE_WEAK_SYMBOLS
__attribute__((weak)) void
_sodium_dummy_symbol_to_prevent_memcmp_lto(const unsigned char *b1,
const unsigned char *b2,
const size_t len)
{
(void) b1;
(void) b2;
(void) len;
}
#endif
int int
sodium_memcmp(const void * const b1_, const void * const b2_, size_t len) sodium_memcmp(const void * const b1_, const void * const b2_, size_t len)
{ {
#ifdef HAVE_WEAK_SYMBOLS
const unsigned char *b1 = (const unsigned char *) b1_; const unsigned char *b1 = (const unsigned char *) b1_;
const unsigned char *b2 = (const unsigned char *) b2_; const unsigned char *b2 = (const unsigned char *) b2_;
#else
const volatile unsigned char *b1 = (const volatile unsigned char *) b1_;
const volatile unsigned char *b2 = (const volatile unsigned char *) b2_;
#endif
size_t i; size_t i;
unsigned char d = (unsigned char) 0U; unsigned char d = (unsigned char) 0U;
#if HAVE_WEAK_SYMBOLS
_sodium_dummy_symbol_to_prevent_memcmp_lto(b1, b2, len);
#endif
for (i = 0U; i < len; i++) { for (i = 0U; i < len; i++) {
d |= b1[i] ^ b2[i]; d |= b1[i] ^ b2[i];
} }