diff options
Diffstat (limited to 'thirdparty/mbedtls/library/constant_time.c')
| -rw-r--r-- | thirdparty/mbedtls/library/constant_time.c | 850 |
1 files changed, 156 insertions, 694 deletions
diff --git a/thirdparty/mbedtls/library/constant_time.c b/thirdparty/mbedtls/library/constant_time.c index 002ca491c6..d212ddfd81 100644 --- a/thirdparty/mbedtls/library/constant_time.c +++ b/thirdparty/mbedtls/library/constant_time.c @@ -10,40 +10,85 @@ * might be translated to branches by some compilers on some platforms. */ +#include <stdint.h> +#include <limits.h> + #include "common.h" #include "constant_time_internal.h" #include "mbedtls/constant_time.h" #include "mbedtls/error.h" #include "mbedtls/platform_util.h" -#if defined(MBEDTLS_BIGNUM_C) -#include "mbedtls/bignum.h" -#endif +#include <string.h> -#if defined(MBEDTLS_SSL_TLS_C) -#include "mbedtls/ssl_internal.h" +#if !defined(MBEDTLS_CT_ASM) +/* + * Define an object with the value zero, such that the compiler cannot prove that it + * has the value zero (because it is volatile, it "may be modified in ways unknown to + * the implementation"). + */ +volatile mbedtls_ct_uint_t mbedtls_ct_zero = 0; #endif -#if defined(MBEDTLS_RSA_C) -#include "mbedtls/rsa.h" -#endif +/* + * Define MBEDTLS_EFFICIENT_UNALIGNED_VOLATILE_ACCESS where assembly is present to + * perform fast unaligned access to volatile data. + * + * This is needed because mbedtls_get_unaligned_uintXX etc don't support volatile + * memory accesses. + * + * Some of these definitions could be moved into alignment.h but for now they are + * only used here. + */ +#if defined(MBEDTLS_EFFICIENT_UNALIGNED_ACCESS) && \ + ((defined(MBEDTLS_CT_ARM_ASM) && (UINTPTR_MAX == 0xfffffffful)) || \ + defined(MBEDTLS_CT_AARCH64_ASM)) +/* We check pointer sizes to avoid issues with them not matching register size requirements */ +#define MBEDTLS_EFFICIENT_UNALIGNED_VOLATILE_ACCESS -#if defined(MBEDTLS_BASE64_C) -#include "constant_time_invasive.h" +static inline uint32_t mbedtls_get_unaligned_volatile_uint32(volatile const unsigned char *p) +{ + /* This is UB, even where it's safe: + * return *((volatile uint32_t*)p); + * so instead the same thing is expressed in assembly below. + */ + uint32_t r; +#if defined(MBEDTLS_CT_ARM_ASM) + asm volatile ("ldr %0, [%1]" : "=r" (r) : "r" (p) :); +#elif defined(MBEDTLS_CT_AARCH64_ASM) + asm volatile ("ldr %w0, [%1]" : "=r" (r) : MBEDTLS_ASM_AARCH64_PTR_CONSTRAINT(p) :); +#else +#error "No assembly defined for mbedtls_get_unaligned_volatile_uint32" #endif - -#include <string.h> + return r; +} +#endif /* defined(MBEDTLS_EFFICIENT_UNALIGNED_ACCESS) && + (defined(MBEDTLS_CT_ARM_ASM) || defined(MBEDTLS_CT_AARCH64_ASM)) */ int mbedtls_ct_memcmp(const void *a, const void *b, size_t n) { - size_t i; + size_t i = 0; + /* + * `A` and `B` are cast to volatile to ensure that the compiler + * generates code that always fully reads both buffers. + * Otherwise it could generate a test to exit early if `diff` has all + * bits set early in the loop. + */ volatile const unsigned char *A = (volatile const unsigned char *) a; volatile const unsigned char *B = (volatile const unsigned char *) b; - volatile unsigned char diff = 0; + uint32_t diff = 0; - for (i = 0; i < n; i++) { +#if defined(MBEDTLS_EFFICIENT_UNALIGNED_VOLATILE_ACCESS) + for (; (i + 4) <= n; i += 4) { + uint32_t x = mbedtls_get_unaligned_volatile_uint32(A + i); + uint32_t y = mbedtls_get_unaligned_volatile_uint32(B + i); + diff |= x ^ y; + } +#endif + + for (; i < n; i++) { /* Read volatile data in order before computing diff. * This avoids IAR compiler warning: * 'the order of volatile accesses is undefined ..' */ @@ -51,330 +96,119 @@ int mbedtls_ct_memcmp(const void *a, diff |= x ^ y; } - return (int) diff; -} - -unsigned mbedtls_ct_uint_mask(unsigned value) -{ - /* MSVC has a warning about unary minus on unsigned, but this is - * well-defined and precisely what we want to do here */ -#if defined(_MSC_VER) -#pragma warning( push ) -#pragma warning( disable : 4146 ) -#endif - return -((value | -value) >> (sizeof(value) * 8 - 1)); -#if defined(_MSC_VER) -#pragma warning( pop ) -#endif -} - -#if defined(MBEDTLS_SSL_SOME_MODES_USE_MAC) || defined(MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC) || \ - defined(MBEDTLS_NIST_KW_C) || defined(MBEDTLS_CIPHER_MODE_CBC) - -size_t mbedtls_ct_size_mask(size_t value) -{ - /* MSVC has a warning about unary minus on unsigned integer types, - * but this is well-defined and precisely what we want to do here. */ -#if defined(_MSC_VER) -#pragma warning( push ) -#pragma warning( disable : 4146 ) -#endif - return -((value | -value) >> (sizeof(value) * 8 - 1)); -#if defined(_MSC_VER) -#pragma warning( pop ) -#endif -} - -#endif /* defined(MBEDTLS_SSL_SOME_MODES_USE_MAC) || defined(MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC) || - defined(MBEDTLS_NIST_KW_C) || defined(MBEDTLS_CIPHER_MODE_CBC) */ - -#if defined(MBEDTLS_BIGNUM_C) - -mbedtls_mpi_uint mbedtls_ct_mpi_uint_mask(mbedtls_mpi_uint value) -{ - /* MSVC has a warning about unary minus on unsigned, but this is - * well-defined and precisely what we want to do here */ -#if defined(_MSC_VER) -#pragma warning( push ) -#pragma warning( disable : 4146 ) -#endif - return -((value | -value) >> (sizeof(value) * 8 - 1)); -#if defined(_MSC_VER) -#pragma warning( pop ) -#endif -} - -#endif /* MBEDTLS_BIGNUM_C */ - -#if defined(MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC) || defined(MBEDTLS_NIST_KW_C) || \ - defined(MBEDTLS_CIPHER_MODE_CBC) - -/** Constant-flow mask generation for "less than" comparison: - * - if \p x < \p y, return all-bits 1, that is (size_t) -1 - * - otherwise, return all bits 0, that is 0 - * - * This function can be used to write constant-time code by replacing branches - * with bit operations using masks. - * - * \param x The first value to analyze. - * \param y The second value to analyze. - * - * \return All-bits-one if \p x is less than \p y, otherwise zero. - */ -static size_t mbedtls_ct_size_mask_lt(size_t x, - size_t y) -{ - /* This has the most significant bit set if and only if x < y */ - const size_t sub = x - y; - - /* sub1 = (x < y) ? 1 : 0 */ - const size_t sub1 = sub >> (sizeof(sub) * 8 - 1); - - /* mask = (x < y) ? 0xff... : 0x00... */ - const size_t mask = mbedtls_ct_size_mask(sub1); - - return mask; -} - -size_t mbedtls_ct_size_mask_ge(size_t x, - size_t y) -{ - return ~mbedtls_ct_size_mask_lt(x, y); -} - -#endif /* defined(MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC) || defined(MBEDTLS_NIST_KW_C) || - defined(MBEDTLS_CIPHER_MODE_CBC) */ -#if defined(MBEDTLS_BASE64_C) - -/* Return 0xff if low <= c <= high, 0 otherwise. - * - * Constant flow with respect to c. - */ -MBEDTLS_STATIC_TESTABLE -unsigned char mbedtls_ct_uchar_mask_of_range(unsigned char low, - unsigned char high, - unsigned char c) -{ - /* low_mask is: 0 if low <= c, 0x...ff if low > c */ - unsigned low_mask = ((unsigned) c - low) >> 8; - /* high_mask is: 0 if c <= high, 0x...ff if c > high */ - unsigned high_mask = ((unsigned) high - c) >> 8; - return ~(low_mask | high_mask) & 0xff; -} - -#endif /* MBEDTLS_BASE64_C */ - -unsigned mbedtls_ct_size_bool_eq(size_t x, - size_t y) -{ - /* diff = 0 if x == y, non-zero otherwise */ - const size_t diff = x ^ y; - - /* MSVC has a warning about unary minus on unsigned integer types, - * but this is well-defined and precisely what we want to do here. */ -#if defined(_MSC_VER) -#pragma warning( push ) -#pragma warning( disable : 4146 ) -#endif - - /* diff_msb's most significant bit is equal to x != y */ - const size_t diff_msb = (diff | (size_t) -diff); - -#if defined(_MSC_VER) -#pragma warning( pop ) -#endif - - /* diff1 = (x != y) ? 1 : 0 */ - const unsigned diff1 = diff_msb >> (sizeof(diff_msb) * 8 - 1); - - return 1 ^ diff1; -} - -#if defined(MBEDTLS_PKCS1_V15) && defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_RSA_ALT) - -/** Constant-flow "greater than" comparison: - * return x > y - * - * This is equivalent to \p x > \p y, but is likely to be compiled - * to code using bitwise operation rather than a branch. - * - * \param x The first value to analyze. - * \param y The second value to analyze. - * - * \return 1 if \p x greater than \p y, otherwise 0. - */ -static unsigned mbedtls_ct_size_gt(size_t x, - size_t y) -{ - /* Return the sign bit (1 for negative) of (y - x). */ - return (y - x) >> (sizeof(size_t) * 8 - 1); -} - -#endif /* MBEDTLS_PKCS1_V15 && MBEDTLS_RSA_C && ! MBEDTLS_RSA_ALT */ - -#if defined(MBEDTLS_BIGNUM_C) - -unsigned mbedtls_ct_mpi_uint_lt(const mbedtls_mpi_uint x, - const mbedtls_mpi_uint y) -{ - mbedtls_mpi_uint ret; - mbedtls_mpi_uint cond; - - /* - * Check if the most significant bits (MSB) of the operands are different. - */ - cond = (x ^ y); - /* - * If the MSB are the same then the difference x-y will be negative (and - * have its MSB set to 1 during conversion to unsigned) if and only if x<y. - */ - ret = (x - y) & ~cond; - /* - * If the MSB are different, then the operand with the MSB of 1 is the - * bigger. (That is if y has MSB of 1, then x<y is true and it is false if - * the MSB of y is 0.) +#if (INT_MAX < INT32_MAX) + /* We don't support int smaller than 32-bits, but if someone tried to build + * with this configuration, there is a risk that, for differing data, the + * only bits set in diff are in the top 16-bits, and would be lost by a + * simple cast from uint32 to int. + * This would have significant security implications, so protect against it. */ +#error "mbedtls_ct_memcmp() requires minimum 32-bit ints" +#else + /* The bit-twiddling ensures that when we cast uint32_t to int, we are casting + * a value that is in the range 0..INT_MAX - a value larger than this would + * result in implementation defined behaviour. + * + * This ensures that the value returned by the function is non-zero iff + * diff is non-zero. */ - ret |= y & cond; - - - ret = ret >> (sizeof(mbedtls_mpi_uint) * 8 - 1); - - return (unsigned) ret; -} - -#endif /* MBEDTLS_BIGNUM_C */ - -unsigned mbedtls_ct_uint_if(unsigned condition, - unsigned if1, - unsigned if0) -{ - unsigned mask = mbedtls_ct_uint_mask(condition); - return (mask & if1) | (~mask & if0); + return (int) ((diff & 0xffff) | (diff >> 16)); +#endif } -#if defined(MBEDTLS_BIGNUM_C) +#if defined(MBEDTLS_NIST_KW_C) -void mbedtls_ct_mpi_uint_cond_assign(size_t n, - mbedtls_mpi_uint *dest, - const mbedtls_mpi_uint *src, - unsigned char condition) +int mbedtls_ct_memcmp_partial(const void *a, + const void *b, + size_t n, + size_t skip_head, + size_t skip_tail) { - size_t i; - - /* MSVC has a warning about unary minus on unsigned integer types, - * but this is well-defined and precisely what we want to do here. */ -#if defined(_MSC_VER) -#pragma warning( push ) -#pragma warning( disable : 4146 ) -#endif + unsigned int diff = 0; - /* all-bits 1 if condition is 1, all-bits 0 if condition is 0 */ - const mbedtls_mpi_uint mask = -condition; + volatile const unsigned char *A = (volatile const unsigned char *) a; + volatile const unsigned char *B = (volatile const unsigned char *) b; -#if defined(_MSC_VER) -#pragma warning( pop ) -#endif + size_t valid_end = n - skip_tail; - for (i = 0; i < n; i++) { - dest[i] = (src[i] & mask) | (dest[i] & ~mask); + for (size_t i = 0; i < n; i++) { + unsigned char x = A[i], y = B[i]; + unsigned int d = x ^ y; + mbedtls_ct_condition_t valid = mbedtls_ct_bool_and(mbedtls_ct_uint_ge(i, skip_head), + mbedtls_ct_uint_lt(i, valid_end)); + diff |= mbedtls_ct_uint_if_else_0(valid, d); } -} - -#endif /* MBEDTLS_BIGNUM_C */ - -#if defined(MBEDTLS_BASE64_C) - -unsigned char mbedtls_ct_base64_enc_char(unsigned char value) -{ - unsigned char digit = 0; - /* For each range of values, if value is in that range, mask digit with - * the corresponding value. Since value can only be in a single range, - * only at most one masking will change digit. */ - digit |= mbedtls_ct_uchar_mask_of_range(0, 25, value) & ('A' + value); - digit |= mbedtls_ct_uchar_mask_of_range(26, 51, value) & ('a' + value - 26); - digit |= mbedtls_ct_uchar_mask_of_range(52, 61, value) & ('0' + value - 52); - digit |= mbedtls_ct_uchar_mask_of_range(62, 62, value) & '+'; - digit |= mbedtls_ct_uchar_mask_of_range(63, 63, value) & '/'; - return digit; -} -signed char mbedtls_ct_base64_dec_value(unsigned char c) -{ - unsigned char val = 0; - /* For each range of digits, if c is in that range, mask val with - * the corresponding value. Since c can only be in a single range, - * only at most one masking will change val. Set val to one plus - * the desired value so that it stays 0 if c is in none of the ranges. */ - val |= mbedtls_ct_uchar_mask_of_range('A', 'Z', c) & (c - 'A' + 0 + 1); - val |= mbedtls_ct_uchar_mask_of_range('a', 'z', c) & (c - 'a' + 26 + 1); - val |= mbedtls_ct_uchar_mask_of_range('0', '9', c) & (c - '0' + 52 + 1); - val |= mbedtls_ct_uchar_mask_of_range('+', '+', c) & (c - '+' + 62 + 1); - val |= mbedtls_ct_uchar_mask_of_range('/', '/', c) & (c - '/' + 63 + 1); - /* At this point, val is 0 if c is an invalid digit and v+1 if c is - * a digit with the value v. */ - return val - 1; + /* Since we go byte-by-byte, the only bits set will be in the bottom 8 bits, so the + * cast from uint to int is safe. */ + return (int) diff; } -#endif /* MBEDTLS_BASE64_C */ +#endif #if defined(MBEDTLS_PKCS1_V15) && defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_RSA_ALT) -/** Shift some data towards the left inside a buffer. - * - * `mbedtls_ct_mem_move_to_left(start, total, offset)` is functionally - * equivalent to - * ``` - * memmove(start, start + offset, total - offset); - * memset(start + offset, 0, total - offset); - * ``` - * but it strives to use a memory access pattern (and thus total timing) - * that does not depend on \p offset. This timing independence comes at - * the expense of performance. - * - * \param start Pointer to the start of the buffer. - * \param total Total size of the buffer. - * \param offset Offset from which to copy \p total - \p offset bytes. - */ -static void mbedtls_ct_mem_move_to_left(void *start, - size_t total, - size_t offset) +void mbedtls_ct_memmove_left(void *start, size_t total, size_t offset) { volatile unsigned char *buf = start; - size_t i, n; - if (total == 0) { - return; - } - for (i = 0; i < total; i++) { - unsigned no_op = mbedtls_ct_size_gt(total - offset, i); + for (size_t i = 0; i < total; i++) { + mbedtls_ct_condition_t no_op = mbedtls_ct_uint_gt(total - offset, i); /* The first `total - offset` passes are a no-op. The last * `offset` passes shift the data one byte to the left and * zero out the last byte. */ - for (n = 0; n < total - 1; n++) { + for (size_t n = 0; n < total - 1; n++) { unsigned char current = buf[n]; - unsigned char next = buf[n+1]; + unsigned char next = buf[n+1]; buf[n] = mbedtls_ct_uint_if(no_op, current, next); } - buf[total-1] = mbedtls_ct_uint_if(no_op, buf[total-1], 0); + buf[total-1] = mbedtls_ct_uint_if_else_0(no_op, buf[total-1]); } } #endif /* MBEDTLS_PKCS1_V15 && MBEDTLS_RSA_C && ! MBEDTLS_RSA_ALT */ -#if defined(MBEDTLS_SSL_SOME_MODES_USE_MAC) -void mbedtls_ct_memcpy_if_eq(unsigned char *dest, - const unsigned char *src, - size_t len, - size_t c1, - size_t c2) -{ - /* mask = c1 == c2 ? 0xff : 0x00 */ - const size_t equal = mbedtls_ct_size_bool_eq(c1, c2); - const unsigned char mask = (unsigned char) mbedtls_ct_size_mask(equal); +void mbedtls_ct_memcpy_if(mbedtls_ct_condition_t condition, + unsigned char *dest, + const unsigned char *src1, + const unsigned char *src2, + size_t len) +{ +#if defined(MBEDTLS_CT_SIZE_64) + const uint64_t mask = (uint64_t) condition; + const uint64_t not_mask = (uint64_t) ~mbedtls_ct_compiler_opaque(condition); +#else + const uint32_t mask = (uint32_t) condition; + const uint32_t not_mask = (uint32_t) ~mbedtls_ct_compiler_opaque(condition); +#endif + + /* If src2 is NULL, setup src2 so that we read from the destination address. + * + * This means that if src2 == NULL && condition is false, the result will be a + * no-op because we read from dest and write the same data back into dest. + */ + if (src2 == NULL) { + src2 = dest; + } /* dest[i] = c1 == c2 ? src[i] : dest[i] */ - for (size_t i = 0; i < len; i++) { - dest[i] = (src[i] & mask) | (dest[i] & ~mask); + size_t i = 0; +#if defined(MBEDTLS_EFFICIENT_UNALIGNED_ACCESS) +#if defined(MBEDTLS_CT_SIZE_64) + for (; (i + 8) <= len; i += 8) { + uint64_t a = mbedtls_get_unaligned_uint64(src1 + i) & mask; + uint64_t b = mbedtls_get_unaligned_uint64(src2 + i) & not_mask; + mbedtls_put_unaligned_uint64(dest + i, a | b); + } +#else + for (; (i + 4) <= len; i += 4) { + uint32_t a = mbedtls_get_unaligned_uint32(src1 + i) & mask; + uint32_t b = mbedtls_get_unaligned_uint32(src2 + i) & not_mask; + mbedtls_put_unaligned_uint32(dest + i, a | b); + } +#endif /* defined(MBEDTLS_CT_SIZE_64) */ +#endif /* MBEDTLS_EFFICIENT_UNALIGNED_ACCESS */ + for (; i < len; i++) { + dest[i] = (src1[i] & mask) | (src2[i] & not_mask); } } @@ -388,399 +222,27 @@ void mbedtls_ct_memcpy_offset(unsigned char *dest, size_t offsetval; for (offsetval = offset_min; offsetval <= offset_max; offsetval++) { - mbedtls_ct_memcpy_if_eq(dest, src + offsetval, len, - offsetval, offset); - } -} - -int mbedtls_ct_hmac(mbedtls_md_context_t *ctx, - const unsigned char *add_data, - size_t add_data_len, - const unsigned char *data, - size_t data_len_secret, - size_t min_data_len, - size_t max_data_len, - unsigned char *output) -{ - /* - * This function breaks the HMAC abstraction and uses the md_clone() - * extension to the MD API in order to get constant-flow behaviour. - * - * HMAC(msg) is defined as HASH(okey + HASH(ikey + msg)) where + means - * concatenation, and okey/ikey are the XOR of the key with some fixed bit - * patterns (see RFC 2104, sec. 2), which are stored in ctx->hmac_ctx. - * - * We'll first compute inner_hash = HASH(ikey + msg) by hashing up to - * minlen, then cloning the context, and for each byte up to maxlen - * finishing up the hash computation, keeping only the correct result. - * - * Then we only need to compute HASH(okey + inner_hash) and we're done. - */ - const mbedtls_md_type_t md_alg = mbedtls_md_get_type(ctx->md_info); - /* TLS 1.0-1.2 only support SHA-384, SHA-256, SHA-1, MD-5, - * all of which have the same block size except SHA-384. */ - const size_t block_size = md_alg == MBEDTLS_MD_SHA384 ? 128 : 64; - const unsigned char * const ikey = ctx->hmac_ctx; - const unsigned char * const okey = ikey + block_size; - const size_t hash_size = mbedtls_md_get_size(ctx->md_info); - - unsigned char aux_out[MBEDTLS_MD_MAX_SIZE]; - mbedtls_md_context_t aux; - size_t offset; - int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; - - mbedtls_md_init(&aux); - -#define MD_CHK(func_call) \ - do { \ - ret = (func_call); \ - if (ret != 0) \ - goto cleanup; \ - } while (0) - - MD_CHK(mbedtls_md_setup(&aux, ctx->md_info, 0)); - - /* After hmac_start() of hmac_reset(), ikey has already been hashed, - * so we can start directly with the message */ - MD_CHK(mbedtls_md_update(ctx, add_data, add_data_len)); - MD_CHK(mbedtls_md_update(ctx, data, min_data_len)); - - /* Fill the hash buffer in advance with something that is - * not a valid hash (barring an attack on the hash and - * deliberately-crafted input), in case the caller doesn't - * check the return status properly. */ - memset(output, '!', hash_size); - - /* For each possible length, compute the hash up to that point */ - for (offset = min_data_len; offset <= max_data_len; offset++) { - MD_CHK(mbedtls_md_clone(&aux, ctx)); - MD_CHK(mbedtls_md_finish(&aux, aux_out)); - /* Keep only the correct inner_hash in the output buffer */ - mbedtls_ct_memcpy_if_eq(output, aux_out, hash_size, - offset, data_len_secret); - - if (offset < max_data_len) { - MD_CHK(mbedtls_md_update(ctx, data + offset, 1)); - } - } - - /* The context needs to finish() before it starts() again */ - MD_CHK(mbedtls_md_finish(ctx, aux_out)); - - /* Now compute HASH(okey + inner_hash) */ - MD_CHK(mbedtls_md_starts(ctx)); - MD_CHK(mbedtls_md_update(ctx, okey, block_size)); - MD_CHK(mbedtls_md_update(ctx, output, hash_size)); - MD_CHK(mbedtls_md_finish(ctx, output)); - - /* Done, get ready for next time */ - MD_CHK(mbedtls_md_hmac_reset(ctx)); - -#undef MD_CHK - -cleanup: - mbedtls_md_free(&aux); - return ret; -} - -#endif /* MBEDTLS_SSL_SOME_MODES_USE_MAC */ - -#if defined(MBEDTLS_BIGNUM_C) - -#define MPI_VALIDATE_RET(cond) \ - MBEDTLS_INTERNAL_VALIDATE_RET(cond, MBEDTLS_ERR_MPI_BAD_INPUT_DATA) - -/* - * Conditionally assign X = Y, without leaking information - * about whether the assignment was made or not. - * (Leaking information about the respective sizes of X and Y is ok however.) - */ -#if defined(_MSC_VER) && defined(_M_ARM64) && (_MSC_FULL_VER < 193131103) -/* - * MSVC miscompiles this function if it's inlined prior to Visual Studio 2022 version 17.1. See: - * https://developercommunity.visualstudio.com/t/c-compiler-miscompiles-part-of-mbedtls-library-on/1646989 - */ -__declspec(noinline) -#endif -int mbedtls_mpi_safe_cond_assign(mbedtls_mpi *X, - const mbedtls_mpi *Y, - unsigned char assign) -{ - int ret = 0; - size_t i; - mbedtls_mpi_uint limb_mask; - MPI_VALIDATE_RET(X != NULL); - MPI_VALIDATE_RET(Y != NULL); - - /* all-bits 1 if assign is 1, all-bits 0 if assign is 0 */ - limb_mask = mbedtls_ct_mpi_uint_mask(assign);; - - MBEDTLS_MPI_CHK(mbedtls_mpi_grow(X, Y->n)); - - X->s = (int) mbedtls_ct_uint_if(assign, Y->s, X->s); - - mbedtls_ct_mpi_uint_cond_assign(Y->n, X->p, Y->p, assign); - - for (i = Y->n; i < X->n; i++) { - X->p[i] &= ~limb_mask; - } - -cleanup: - return ret; -} - -/* - * Conditionally swap X and Y, without leaking information - * about whether the swap was made or not. - * Here it is not ok to simply swap the pointers, which would lead to - * different memory access patterns when X and Y are used afterwards. - */ -int mbedtls_mpi_safe_cond_swap(mbedtls_mpi *X, - mbedtls_mpi *Y, - unsigned char swap) -{ - int ret, s; - size_t i; - mbedtls_mpi_uint limb_mask; - mbedtls_mpi_uint tmp; - MPI_VALIDATE_RET(X != NULL); - MPI_VALIDATE_RET(Y != NULL); - - if (X == Y) { - return 0; + mbedtls_ct_memcpy_if(mbedtls_ct_uint_eq(offsetval, offset), dest, src + offsetval, NULL, + len); } - - /* all-bits 1 if swap is 1, all-bits 0 if swap is 0 */ - limb_mask = mbedtls_ct_mpi_uint_mask(swap); - - MBEDTLS_MPI_CHK(mbedtls_mpi_grow(X, Y->n)); - MBEDTLS_MPI_CHK(mbedtls_mpi_grow(Y, X->n)); - - s = X->s; - X->s = (int) mbedtls_ct_uint_if(swap, Y->s, X->s); - Y->s = (int) mbedtls_ct_uint_if(swap, s, Y->s); - - - for (i = 0; i < X->n; i++) { - tmp = X->p[i]; - X->p[i] = (X->p[i] & ~limb_mask) | (Y->p[i] & limb_mask); - Y->p[i] = (Y->p[i] & ~limb_mask) | (tmp & limb_mask); - } - -cleanup: - return ret; } -/* - * Compare signed values in constant time - */ -int mbedtls_mpi_lt_mpi_ct(const mbedtls_mpi *X, - const mbedtls_mpi *Y, - unsigned *ret) -{ - size_t i; - /* The value of any of these variables is either 0 or 1 at all times. */ - unsigned cond, done, X_is_negative, Y_is_negative; - - MPI_VALIDATE_RET(X != NULL); - MPI_VALIDATE_RET(Y != NULL); - MPI_VALIDATE_RET(ret != NULL); - - if (X->n != Y->n) { - return MBEDTLS_ERR_MPI_BAD_INPUT_DATA; - } - - /* - * Set sign_N to 1 if N >= 0, 0 if N < 0. - * We know that N->s == 1 if N >= 0 and N->s == -1 if N < 0. - */ - X_is_negative = (X->s & 2) >> 1; - Y_is_negative = (Y->s & 2) >> 1; - - /* - * If the signs are different, then the positive operand is the bigger. - * That is if X is negative (X_is_negative == 1), then X < Y is true and it - * is false if X is positive (X_is_negative == 0). - */ - cond = (X_is_negative ^ Y_is_negative); - *ret = cond & X_is_negative; - - /* - * This is a constant-time function. We might have the result, but we still - * need to go through the loop. Record if we have the result already. - */ - done = cond; - - for (i = X->n; i > 0; i--) { - /* - * If Y->p[i - 1] < X->p[i - 1] then X < Y is true if and only if both - * X and Y are negative. - * - * Again even if we can make a decision, we just mark the result and - * the fact that we are done and continue looping. - */ - cond = mbedtls_ct_mpi_uint_lt(Y->p[i - 1], X->p[i - 1]); - *ret |= cond & (1 - done) & X_is_negative; - done |= cond; - - /* - * If X->p[i - 1] < Y->p[i - 1] then X < Y is true if and only if both - * X and Y are positive. - * - * Again even if we can make a decision, we just mark the result and - * the fact that we are done and continue looping. - */ - cond = mbedtls_ct_mpi_uint_lt(X->p[i - 1], Y->p[i - 1]); - *ret |= cond & (1 - done) & (1 - X_is_negative); - done |= cond; - } - - return 0; -} - -#endif /* MBEDTLS_BIGNUM_C */ - #if defined(MBEDTLS_PKCS1_V15) && defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_RSA_ALT) -int mbedtls_ct_rsaes_pkcs1_v15_unpadding(int mode, - unsigned char *input, - size_t ilen, - unsigned char *output, - size_t output_max_len, - size_t *olen) +void mbedtls_ct_zeroize_if(mbedtls_ct_condition_t condition, void *buf, size_t len) { - int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; - size_t i, plaintext_max_size; - - /* The following variables take sensitive values: their value must - * not leak into the observable behavior of the function other than - * the designated outputs (output, olen, return value). Otherwise - * this would open the execution of the function to - * side-channel-based variants of the Bleichenbacher padding oracle - * attack. Potential side channels include overall timing, memory - * access patterns (especially visible to an adversary who has access - * to a shared memory cache), and branches (especially visible to - * an adversary who has access to a shared code cache or to a shared - * branch predictor). */ - size_t pad_count = 0; - unsigned bad = 0; - unsigned char pad_done = 0; - size_t plaintext_size = 0; - unsigned output_too_large; - - plaintext_max_size = (output_max_len > ilen - 11) ? ilen - 11 - : output_max_len; - - /* Check and get padding length in constant time and constant - * memory trace. The first byte must be 0. */ - bad |= input[0]; - - if (mode == MBEDTLS_RSA_PRIVATE) { - /* Decode EME-PKCS1-v1_5 padding: 0x00 || 0x02 || PS || 0x00 - * where PS must be at least 8 nonzero bytes. */ - bad |= input[1] ^ MBEDTLS_RSA_CRYPT; - - /* Read the whole buffer. Set pad_done to nonzero if we find - * the 0x00 byte and remember the padding length in pad_count. */ - for (i = 2; i < ilen; i++) { - pad_done |= ((input[i] | (unsigned char) -input[i]) >> 7) ^ 1; - pad_count += ((pad_done | (unsigned char) -pad_done) >> 7) ^ 1; - } - } else { - /* Decode EMSA-PKCS1-v1_5 padding: 0x00 || 0x01 || PS || 0x00 - * where PS must be at least 8 bytes with the value 0xFF. */ - bad |= input[1] ^ MBEDTLS_RSA_SIGN; - - /* Read the whole buffer. Set pad_done to nonzero if we find - * the 0x00 byte and remember the padding length in pad_count. - * If there's a non-0xff byte in the padding, the padding is bad. */ - for (i = 2; i < ilen; i++) { - pad_done |= mbedtls_ct_uint_if(input[i], 0, 1); - pad_count += mbedtls_ct_uint_if(pad_done, 0, 1); - bad |= mbedtls_ct_uint_if(pad_done, 0, input[i] ^ 0xFF); - } + uint32_t mask = (uint32_t) ~condition; + uint8_t *p = (uint8_t *) buf; + size_t i = 0; +#if defined(MBEDTLS_EFFICIENT_UNALIGNED_ACCESS) + for (; (i + 4) <= len; i += 4) { + mbedtls_put_unaligned_uint32((void *) (p + i), + mbedtls_get_unaligned_uint32((void *) (p + i)) & mask); } - - /* If pad_done is still zero, there's no data, only unfinished padding. */ - bad |= mbedtls_ct_uint_if(pad_done, 0, 1); - - /* There must be at least 8 bytes of padding. */ - bad |= mbedtls_ct_size_gt(8, pad_count); - - /* If the padding is valid, set plaintext_size to the number of - * remaining bytes after stripping the padding. If the padding - * is invalid, avoid leaking this fact through the size of the - * output: use the maximum message size that fits in the output - * buffer. Do it without branches to avoid leaking the padding - * validity through timing. RSA keys are small enough that all the - * size_t values involved fit in unsigned int. */ - plaintext_size = mbedtls_ct_uint_if( - bad, (unsigned) plaintext_max_size, - (unsigned) (ilen - pad_count - 3)); - - /* Set output_too_large to 0 if the plaintext fits in the output - * buffer and to 1 otherwise. */ - output_too_large = mbedtls_ct_size_gt(plaintext_size, - plaintext_max_size); - - /* Set ret without branches to avoid timing attacks. Return: - * - INVALID_PADDING if the padding is bad (bad != 0). - * - OUTPUT_TOO_LARGE if the padding is good but the decrypted - * plaintext does not fit in the output buffer. - * - 0 if the padding is correct. */ - ret = -(int) mbedtls_ct_uint_if( - bad, -MBEDTLS_ERR_RSA_INVALID_PADDING, - mbedtls_ct_uint_if(output_too_large, - -MBEDTLS_ERR_RSA_OUTPUT_TOO_LARGE, - 0)); - - /* If the padding is bad or the plaintext is too large, zero the - * data that we're about to copy to the output buffer. - * We need to copy the same amount of data - * from the same buffer whether the padding is good or not to - * avoid leaking the padding validity through overall timing or - * through memory or cache access patterns. */ - bad = mbedtls_ct_uint_mask(bad | output_too_large); - for (i = 11; i < ilen; i++) { - input[i] &= ~bad; - } - - /* If the plaintext is too large, truncate it to the buffer size. - * Copy anyway to avoid revealing the length through timing, because - * revealing the length is as bad as revealing the padding validity - * for a Bleichenbacher attack. */ - plaintext_size = mbedtls_ct_uint_if(output_too_large, - (unsigned) plaintext_max_size, - (unsigned) plaintext_size); - - /* Move the plaintext to the leftmost position where it can start in - * the working buffer, i.e. make it start plaintext_max_size from - * the end of the buffer. Do this with a memory access trace that - * does not depend on the plaintext size. After this move, the - * starting location of the plaintext is no longer sensitive - * information. */ - mbedtls_ct_mem_move_to_left(input + ilen - plaintext_max_size, - plaintext_max_size, - plaintext_max_size - plaintext_size); - - /* Finally copy the decrypted plaintext plus trailing zeros into the output - * buffer. If output_max_len is 0, then output may be an invalid pointer - * and the result of memcpy() would be undefined; prevent undefined - * behavior making sure to depend only on output_max_len (the size of the - * user-provided output buffer), which is independent from plaintext - * length, validity of padding, success of the decryption, and other - * secrets. */ - if (output_max_len != 0) { - memcpy(output, input + ilen - plaintext_max_size, plaintext_max_size); +#endif + for (; i < len; i++) { + p[i] = p[i] & mask; } - - /* Report the amount of data we copied to the output buffer. In case - * of errors (bad padding or output too large), the value of *olen - * when this function returns is not specified. Making it equivalent - * to the good case limits the risks of leaking the padding validity. */ - *olen = plaintext_size; - - return ret; } -#endif /* MBEDTLS_PKCS1_V15 && MBEDTLS_RSA_C && ! MBEDTLS_RSA_ALT */ +#endif /* defined(MBEDTLS_PKCS1_V15) && defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_RSA_ALT) */ |