/* * Copyright 2014-2021 The OpenSSL Project Authors. All Rights Reserved. * * Licensed under the Apache License 2.0 (the "License"). You may not use * this file except in compliance with the License. You can obtain a copy * in the file LICENSE in the source distribution or at * https://www.openssl.org/source/license.html */ #ifndef OSSL_INTERNAL_CONSTANT_TIME_H # define OSSL_INTERNAL_CONSTANT_TIME_H # pragma once # include <stdlib.h> # include <string.h> # include <openssl/e_os2.h> /* For 'ossl_inline' */ /*- * The boolean methods return a bitmask of all ones (0xff...f) for true * and 0 for false. This is useful for choosing a value based on the result * of a conditional in constant time. For example, * if (a < b) { * c = a; * } else { * c = b; * } * can be written as * unsigned int lt = constant_time_lt(a, b); * c = constant_time_select(lt, a, b); */ /* Returns the given value with the MSB copied to all the other bits. */ static ossl_inline unsigned int constant_time_msb(unsigned int a); /* Convenience method for uint32_t. */ static ossl_inline uint32_t constant_time_msb_32(uint32_t a); /* Convenience method for uint64_t. */ static ossl_inline uint64_t constant_time_msb_64(uint64_t a); /* Returns 0xff..f if a < b and 0 otherwise. */ static ossl_inline unsigned int constant_time_lt(unsigned int a, unsigned int b); /* Convenience method for getting an 8-bit mask. */ static ossl_inline unsigned char constant_time_lt_8(unsigned int a, unsigned int b); /* Convenience method for uint64_t. */ static ossl_inline uint64_t constant_time_lt_64(uint64_t a, uint64_t b); /* Returns 0xff..f if a >= b and 0 otherwise. */ static ossl_inline unsigned int constant_time_ge(unsigned int a, unsigned int b); /* Convenience method for getting an 8-bit mask. */ static ossl_inline unsigned char constant_time_ge_8(unsigned int a, unsigned int b); /* Returns 0xff..f if a == 0 and 0 otherwise. */ static ossl_inline unsigned int constant_time_is_zero(unsigned int a); /* Convenience method for getting an 8-bit mask. */ static ossl_inline unsigned char constant_time_is_zero_8(unsigned int a); /* Convenience method for getting a 32-bit mask. */ static ossl_inline uint32_t constant_time_is_zero_32(uint32_t a); /* Returns 0xff..f if a == b and 0 otherwise. */ static ossl_inline unsigned int constant_time_eq(unsigned int a, unsigned int b); /* Convenience method for getting an 8-bit mask. */ static ossl_inline unsigned char constant_time_eq_8(unsigned int a, unsigned int b); /* Signed integers. */ static ossl_inline unsigned int constant_time_eq_int(int a, int b); /* Convenience method for getting an 8-bit mask. */ static ossl_inline unsigned char constant_time_eq_int_8(int a, int b); /*- * Returns (mask & a) | (~mask & b). * * When |mask| is all 1s or all 0s (as returned by the methods above), * the select methods return either |a| (if |mask| is nonzero) or |b| * (if |mask| is zero). */ static ossl_inline unsigned int constant_time_select(unsigned int mask, unsigned int a, unsigned int b); /* Convenience method for unsigned chars. */ static ossl_inline unsigned char constant_time_select_8(unsigned char mask, unsigned char a, unsigned char b); /* Convenience method for uint32_t. */ static ossl_inline uint32_t constant_time_select_32(uint32_t mask, uint32_t a, uint32_t b); /* Convenience method for uint64_t. */ static ossl_inline uint64_t constant_time_select_64(uint64_t mask, uint64_t a, uint64_t b); /* Convenience method for signed integers. */ static ossl_inline int constant_time_select_int(unsigned int mask, int a, int b); static ossl_inline unsigned int constant_time_msb(unsigned int a) { return 0 - (a >> (sizeof(a) * 8 - 1)); } static ossl_inline uint32_t constant_time_msb_32(uint32_t a) { return 0 - (a >> 31); } static ossl_inline uint64_t constant_time_msb_64(uint64_t a) { return 0 - (a >> 63); } static ossl_inline size_t constant_time_msb_s(size_t a) { return 0 - (a >> (sizeof(a) * 8 - 1)); } static ossl_inline unsigned int constant_time_lt(unsigned int a, unsigned int b) { return constant_time_msb(a ^ ((a ^ b) | ((a - b) ^ b))); } static ossl_inline size_t constant_time_lt_s(size_t a, size_t b) { return constant_time_msb_s(a ^ ((a ^ b) | ((a - b) ^ b))); } static ossl_inline unsigned char constant_time_lt_8(unsigned int a, unsigned int b) { return (unsigned char)constant_time_lt(a, b); } static ossl_inline uint64_t constant_time_lt_64(uint64_t a, uint64_t b) { return constant_time_msb_64(a ^ ((a ^ b) | ((a - b) ^ b))); } static ossl_inline unsigned int constant_time_ge(unsigned int a, unsigned int b) { return ~constant_time_lt(a, b); } static ossl_inline size_t constant_time_ge_s(size_t a, size_t b) { return ~constant_time_lt_s(a, b); } static ossl_inline unsigned char constant_time_ge_8(unsigned int a, unsigned int b) { return (unsigned char)constant_time_ge(a, b); } static ossl_inline unsigned char constant_time_ge_8_s(size_t a, size_t b) { return (unsigned char)constant_time_ge_s(a, b); } static ossl_inline unsigned int constant_time_is_zero(unsigned int a) { return constant_time_msb(~a & (a - 1)); } static ossl_inline size_t constant_time_is_zero_s(size_t a) { return constant_time_msb_s(~a & (a - 1)); } static ossl_inline unsigned char constant_time_is_zero_8(unsigned int a) { return (unsigned char)constant_time_is_zero(a); } static ossl_inline uint32_t constant_time_is_zero_32(uint32_t a) { return constant_time_msb_32(~a & (a - 1)); } static ossl_inline uint64_t constant_time_is_zero_64(uint64_t a) { return constant_time_msb_64(~a & (a - 1)); } static ossl_inline unsigned int constant_time_eq(unsigned int a, unsigned int b) { return constant_time_is_zero(a ^ b); } static ossl_inline size_t constant_time_eq_s(size_t a, size_t b) { return constant_time_is_zero_s(a ^ b); } static ossl_inline unsigned char constant_time_eq_8(unsigned int a, unsigned int b) { return (unsigned char)constant_time_eq(a, b); } static ossl_inline unsigned char constant_time_eq_8_s(size_t a, size_t b) { return (unsigned char)constant_time_eq_s(a, b); } static ossl_inline unsigned int constant_time_eq_int(int a, int b) { return constant_time_eq((unsigned)(a), (unsigned)(b)); } 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 (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 (value_barrier_s(mask) & a) | (value_barrier_s(~mask) & b); } static ossl_inline unsigned char constant_time_select_8(unsigned char mask, unsigned char a, unsigned char b) { return (unsigned char)constant_time_select(mask, a, b); } static ossl_inline int constant_time_select_int(unsigned int mask, int a, int b) { return (int)constant_time_select(mask, (unsigned)(a), (unsigned)(b)); } static ossl_inline int constant_time_select_int_s(size_t mask, int a, int b) { return (int)constant_time_select((unsigned)mask, (unsigned)(a), (unsigned)(b)); } static ossl_inline uint32_t constant_time_select_32(uint32_t mask, uint32_t a, uint32_t 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 (value_barrier_64(mask) & a) | (value_barrier_64(~mask) & b); } /* * mask must be 0xFFFFFFFF or 0x00000000. * * if (mask) { * uint32_t tmp = *a; * * *a = *b; * *b = tmp; * } */ static ossl_inline void constant_time_cond_swap_32(uint32_t mask, uint32_t *a, uint32_t *b) { uint32_t xor = *a ^ *b; xor &= mask; *a ^= xor; *b ^= xor; } /* * mask must be 0xFFFFFFFF or 0x00000000. * * if (mask) { * uint64_t tmp = *a; * * *a = *b; * *b = tmp; * } */ static ossl_inline void constant_time_cond_swap_64(uint64_t mask, uint64_t *a, uint64_t *b) { uint64_t xor = *a ^ *b; xor &= mask; *a ^= xor; *b ^= xor; } /* * mask must be 0xFF or 0x00. * "constant time" is per len. * * if (mask) { * unsigned char tmp[len]; * * memcpy(tmp, a, len); * memcpy(a, b); * memcpy(b, tmp); * } */ static ossl_inline void constant_time_cond_swap_buff(unsigned char mask, unsigned char *a, unsigned char *b, size_t len) { size_t i; unsigned char tmp; for (i = 0; i < len; i++) { tmp = a[i] ^ b[i]; tmp &= mask; a[i] ^= tmp; b[i] ^= tmp; } } /* * table is a two dimensional array of bytes. Each row has rowsize elements. * Copies row number idx into out. rowsize and numrows are not considered * private. */ static ossl_inline void constant_time_lookup(void *out, const void *table, size_t rowsize, size_t numrows, size_t idx) { size_t i, j; const unsigned char *tablec = (const unsigned char *)table; unsigned char *outc = (unsigned char *)out; unsigned char mask; memset(out, 0, rowsize); /* Note idx may underflow - but that is well defined */ for (i = 0; i < numrows; i++, idx--) { mask = (unsigned char)constant_time_is_zero_s(idx); for (j = 0; j < rowsize; j++) *(outc + j) |= constant_time_select_8(mask, *(tablec++), 0); } } /* * Expected usage pattern is to unconditionally set error and then * wipe it if there was no actual error. |clear| is 1 or 0. */ void err_clear_last_constant_time(int clear); #endif /* OSSL_INTERNAL_CONSTANT_TIME_H */