diff options
Diffstat (limited to 'include/internal/constant_time_locl.h')
| -rw-r--r-- | include/internal/constant_time_locl.h | 64 |
1 files changed, 59 insertions, 5 deletions
diff --git a/include/internal/constant_time_locl.h b/include/internal/constant_time_locl.h index cde30f4067ef..0193a653d4bb 100644 --- a/include/internal/constant_time_locl.h +++ b/include/internal/constant_time_locl.h @@ -1,5 +1,5 @@ /* - * Copyright 2014-2018 The OpenSSL Project Authors. All Rights Reserved. + * Copyright 2014-2019 The OpenSSL Project Authors. All Rights Reserved. * * Licensed under the OpenSSL license (the "License"). You may not use * this file except in compliance with the License. You can obtain a copy @@ -213,18 +213,72 @@ static ossl_inline unsigned char constant_time_eq_int_8(int a, int b) return constant_time_eq_8((unsigned)(a), (unsigned)(b)); } +/* + * Returns the value unmodified, but avoids optimizations. + * The barriers prevent the compiler from narrowing down the + * possible value range of the mask and ~mask in the select + * statements, which avoids the recognition of the select + * and turning it into a conditional load or branch. + */ +static ossl_inline unsigned int value_barrier(unsigned int a) +{ +#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__) + unsigned int r; + __asm__("" : "=r"(r) : "0"(a)); +#else + volatile unsigned int r = a; +#endif + return r; +} + +/* Convenience method for uint32_t. */ +static ossl_inline uint32_t value_barrier_32(uint32_t a) +{ +#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__) + uint32_t r; + __asm__("" : "=r"(r) : "0"(a)); +#else + volatile uint32_t r = a; +#endif + return r; +} + +/* Convenience method for uint64_t. */ +static ossl_inline uint64_t value_barrier_64(uint64_t a) +{ +#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__) + uint64_t r; + __asm__("" : "=r"(r) : "0"(a)); +#else + volatile uint64_t r = a; +#endif + return r; +} + +/* Convenience method for size_t. */ +static ossl_inline size_t value_barrier_s(size_t a) +{ +#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__) + size_t r; + __asm__("" : "=r"(r) : "0"(a)); +#else + volatile size_t r = a; +#endif + return r; +} + static ossl_inline unsigned int constant_time_select(unsigned int mask, unsigned int a, unsigned int b) { - return (mask & a) | (~mask & b); + return (value_barrier(mask) & a) | (value_barrier(~mask) & b); } static ossl_inline size_t constant_time_select_s(size_t mask, size_t a, size_t b) { - return (mask & a) | (~mask & b); + return (value_barrier_s(mask) & a) | (value_barrier_s(~mask) & b); } static ossl_inline unsigned char constant_time_select_8(unsigned char mask, @@ -249,13 +303,13 @@ static ossl_inline int constant_time_select_int_s(size_t mask, int a, int b) static ossl_inline uint32_t constant_time_select_32(uint32_t mask, uint32_t a, uint32_t b) { - return (mask & a) | (~mask & b); + return (value_barrier_32(mask) & a) | (value_barrier_32(~mask) & b); } static ossl_inline uint64_t constant_time_select_64(uint64_t mask, uint64_t a, uint64_t b) { - return (mask & a) | (~mask & b); + return (value_barrier_64(mask) & a) | (value_barrier_64(~mask) & b); } /* |