constant_time.c | Explore in Territory

/**
 *  Constant-time functions
 *
 *  Copyright The Mbed TLS Contributors
 *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
 */

/*
 * The following functions are implemented without using comparison operators, as those
 * 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"

#include <string.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

/*
 * 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

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
    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)
{ … }

#if defined(MBEDTLS_NIST_KW_C)

int mbedtls_ct_memcmp_partial(const void *a,
                              const void *b,
                              size_t n,
                              size_t skip_head,
                              size_t skip_tail)
{ … }

#endif

#if defined(MBEDTLS_PKCS1_V15) && defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_RSA_ALT)

void mbedtls_ct_memmove_left(void *start, size_t total, size_t offset)
{ … }

#endif /* MBEDTLS_PKCS1_V15 && MBEDTLS_RSA_C && ! MBEDTLS_RSA_ALT */

void mbedtls_ct_memcpy_if(mbedtls_ct_condition_t condition,
                          unsigned char *dest,
                          const unsigned char *src1,
                          const unsigned char *src2,
                          size_t len)
{ … }

void mbedtls_ct_memcpy_offset(unsigned char *dest,
                              const unsigned char *src,
                              size_t offset,
                              size_t offset_min,
                              size_t offset_max,
                              size_t len)
{ … }

#if defined(MBEDTLS_PKCS1_V15) && defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_RSA_ALT)

void mbedtls_ct_zeroize_if(mbedtls_ct_condition_t condition, void *buf, size_t len)
{ … }

#endif /* defined(MBEDTLS_PKCS1_V15) && defined(MBEDTLS_RSA_C) && !defined(MBEDTLS_RSA_ALT) */
godot/thirdparty/mbedtls/library/constant_time.c
