library/platform_util.c

/*
 * Common and shared functions used by multiple modules in the Mbed TLS
 * library.
 *
 *  Copyright (C) 2018, Arm Limited, All Rights Reserved
 *  SPDX-License-Identifier: Apache-2.0
 *
 *  Licensed under the Apache License, Version 2.0 (the "License"); you may
 *  not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 *  This file is part of Mbed TLS (https://tls.mbed.org)
 */

/*
 * Ensure gmtime_r is available even with -std=c99; must be defined before
 * config.h, which pulls in glibc's features.h. Harmless on other platforms.
 */
#if !defined(_POSIX_C_SOURCE)
#define _POSIX_C_SOURCE 200112L
#endif

#if !defined(MBEDTLS_CONFIG_FILE)
#include "mbedtls/config.h"
#else
#include MBEDTLS_CONFIG_FILE
#endif

#include "mbedtls/platform_util.h"
#include "mbedtls/platform.h"
#include "mbedtls/threading.h"

#if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
#include "mbedtls/entropy_poll.h"
#endif

#include <stddef.h>
#include <string.h>

#if !defined(MBEDTLS_PLATFORM_ZEROIZE_ALT)
/*
 * This implementation should never be optimized out by the compiler
 *
 * This implementation for mbedtls_platform_zeroize() was inspired from Colin
 * Percival's blog article at:
 *
 * http://www.daemonology.net/blog/2014-09-04-how-to-zero-a-buffer.html
 *
 * It uses a volatile function pointer to the standard memset(). Because the
 * pointer is volatile the compiler expects it to change at
 * any time and will not optimize out the call that could potentially perform
 * other operations on the input buffer instead of just setting it to 0.
 * Nevertheless, as pointed out by davidtgoldblatt on Hacker News
 * (refer to http://www.daemonology.net/blog/2014-09-05-erratum.html for
 * details), optimizations of the following form are still possible:
 *
 * if( memset_func != memset )
 *     memset_func( buf, 0, len );
 *
 * Note that it is extremely difficult to guarantee that
 * mbedtls_platform_zeroize() will not be optimized out by aggressive compilers
 * in a portable way. For this reason, Mbed TLS also provides the configuration
 * option MBEDTLS_PLATFORM_ZEROIZE_ALT, which allows users to configure
 * mbedtls_platform_zeroize() to use a suitable implementation for their
 * platform and needs.
 */
void *mbedtls_platform_memset( void *, int, size_t );
static void * (* const volatile memset_func)( void *, int, size_t ) = mbedtls_platform_memset;

void mbedtls_platform_zeroize( void *buf, size_t len )
{
    MBEDTLS_INTERNAL_VALIDATE( len == 0 || buf != NULL );

    if( len > 0 )
        memset_func( buf, 0, len );
}
#endif /* MBEDTLS_PLATFORM_ZEROIZE_ALT */

void *mbedtls_platform_memset( void *ptr, int value, size_t num )
{
    /* Randomize start offset. */
    size_t start_offset = (size_t) mbedtls_platform_random_in_range( num );
    /* Randomize data */
    uint32_t data = mbedtls_platform_random_in_range( 256 );

    /* Perform a pair of memset operations from random locations with
     * random data */
    memset( (void *) ( (unsigned char *) ptr + start_offset ), data,
            ( num - start_offset ) );
    memset( (void *) ptr, data, start_offset );

    /* Perform the original memset */
    return( memset( ptr, value, num ) );
}

void *mbedtls_platform_memcpy( void *dst, const void *src, size_t num )
{
    /* Randomize start offset. */
    size_t start_offset = (size_t) mbedtls_platform_random_in_range( num );
    /* Randomize initial data to prevent leakage while copying */
    uint32_t data = mbedtls_platform_random_in_range( 256 );

    memset( (void *) dst, data, num );
    memcpy( (void *) ( (unsigned char *) dst + start_offset ),
            (void *) ( (unsigned char *) src + start_offset ),
            ( num - start_offset ) );
    return( memcpy( (void *) dst, (void *) src, start_offset ) );
}

int mbedtls_platform_memcmp( const void *buf1, const void *buf2, size_t num )
{
    volatile const unsigned char *A = (volatile const unsigned char *) buf1;
    volatile const unsigned char *B = (volatile const unsigned char *) buf2;
    volatile unsigned char diff = 0;

    size_t i = num;

    size_t start_offset = (size_t) mbedtls_platform_random_in_range( num );

    for( i = start_offset; i < num; i++ )
    {
        unsigned char x = A[i], y = B[i];
        diff |= x ^ y;
    }

    for( i = 0; i < start_offset; i++ )
    {
        unsigned char x = A[i], y = B[i];
        diff |= x ^ y;
    }

    return( diff );
}

uint32_t mbedtls_platform_random_in_range( size_t num )
{
    /* Temporary force the dummy version - drawing directly from the HRNG
     * seems to be causing issues, avoid doing that until we understood the
     * issue, and perhaps we'll need to draw from a DRBG instead. */
#if 1 || !defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
    (void) num;
    return 0;
#else
    uint32_t result = 0;
    size_t olen = 0;

    mbedtls_hardware_poll( NULL, (unsigned char *) &result, sizeof( result ),
                           &olen );

    if( num == 0 )
    {
        result = 0;
    }
    else
    {
        result %= num;
    }

    return( result );
#endif
}

/* Some compilers (armcc 5 for example) optimize away successive reads from a
 * volatile local variable (which we use as a counter-measure to fault
 * injection attacks), unless there is a call to an external function between
 * them. This functions doesn't need to do anything, it just needs to be
 * in another compilation unit. So here's a function that does nothing. */
void mbedtls_platform_enforce_volatile_reads( void )
{
}

#if defined(MBEDTLS_HAVE_TIME_DATE) && !defined(MBEDTLS_PLATFORM_GMTIME_R_ALT)
#include <time.h>
#if !defined(_WIN32) && (defined(unix) || \
    defined(__unix) || defined(__unix__) || (defined(__APPLE__) && \
    defined(__MACH__)))
#include <unistd.h>
#endif /* !_WIN32 && (unix || __unix || __unix__ ||
        * (__APPLE__ && __MACH__)) */

#if !( ( defined(_POSIX_VERSION) && _POSIX_VERSION >= 200809L ) ||     \
       ( defined(_POSIX_THREAD_SAFE_FUNCTIONS ) &&                     \
         _POSIX_THREAD_SAFE_FUNCTIONS >= 20112L ) )
/*
 * This is a convenience shorthand macro to avoid checking the long
 * preprocessor conditions above. Ideally, we could expose this macro in
 * platform_util.h and simply use it in platform_util.c, threading.c and
 * threading.h. However, this macro is not part of the Mbed TLS public API, so
 * we keep it private by only defining it in this file
 */
#if ! ( defined(_WIN32) && !defined(EFIX64) && !defined(EFI32) )
#define PLATFORM_UTIL_USE_GMTIME
#endif /* ! ( defined(_WIN32) && !defined(EFIX64) && !defined(EFI32) ) */

#endif /* !( ( defined(_POSIX_VERSION) && _POSIX_VERSION >= 200809L ) ||     \
             ( defined(_POSIX_THREAD_SAFE_FUNCTIONS ) &&                     \
                _POSIX_THREAD_SAFE_FUNCTIONS >= 20112L ) ) */

struct tm *mbedtls_platform_gmtime_r( const mbedtls_time_t *tt,
                                      struct tm *tm_buf )
{
#if defined(_WIN32) && !defined(EFIX64) && !defined(EFI32)
    return( ( gmtime_s( tm_buf, tt ) == 0 ) ? tm_buf : NULL );
#elif !defined(PLATFORM_UTIL_USE_GMTIME)
    return( gmtime_r( tt, tm_buf ) );
#else
    struct tm *lt;

#if defined(MBEDTLS_THREADING_C)
    if( mbedtls_mutex_lock( &mbedtls_threading_gmtime_mutex ) != 0 )
        return( NULL );
#endif /* MBEDTLS_THREADING_C */

    lt = gmtime( tt );

    if( lt != NULL )
    {
        memcpy( tm_buf, lt, sizeof( struct tm ) );
    }

#if defined(MBEDTLS_THREADING_C)
    if( mbedtls_mutex_unlock( &mbedtls_threading_gmtime_mutex ) != 0 )
        return( NULL );
#endif /* MBEDTLS_THREADING_C */

    return( ( lt == NULL ) ? NULL : tm_buf );
#endif /* _WIN32 && !EFIX64 && !EFI32 */
}
#endif /* MBEDTLS_HAVE_TIME_DATE && MBEDTLS_PLATFORM_GMTIME_R_ALT */

unsigned char* mbedtls_platform_put_uint32_be( unsigned char *buf,
                                               size_t num )
{
    *buf++ = (unsigned char) ( num >> 24 );
    *buf++ = (unsigned char) ( num >> 16 );
    *buf++ = (unsigned char) ( num >> 8  );
    *buf++ = (unsigned char) ( num       );

    return buf;
}

unsigned char* mbedtls_platform_put_uint24_be( unsigned char *buf,
                                               size_t num )
{
    *buf++ = (unsigned char) ( num >> 16 );
    *buf++ = (unsigned char) ( num >> 8  );
    *buf++ = (unsigned char) ( num       );

    return buf;
}

unsigned char* mbedtls_platform_put_uint16_be( unsigned char *buf,
                                               size_t num )
{
    *buf++ = (unsigned char) ( num >> 8 );
    *buf++ = (unsigned char) ( num      );

    return buf;
}

size_t mbedtls_platform_get_uint32_be( const unsigned char *buf )
{
    return ( ( (unsigned int) buf[0] << 24 ) |
             ( (unsigned int) buf[1] << 16 ) |
             ( (unsigned int) buf[2] <<  8 ) |
             ( (unsigned int) buf[3]       ) );
}

size_t mbedtls_platform_get_uint24_be( const unsigned char *buf )
{
    return ( ( buf[0] << 16 ) |
             ( buf[1] <<  8)  |
             ( buf[2]      ) );
}

size_t mbedtls_platform_get_uint16_be( const unsigned char *buf )
{
    return ( ( buf[0] << 8 )  |
             ( buf[1]      ) );
}