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/*
* Entropy accumulator implementation
*
* Copyright The Mbed TLS Contributors
* SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
*/
#include "common.h"
#if defined(MBEDTLS_ENTROPY_C)
#include "mbedtls/entropy.h"
#include "entropy_poll.h"
#include "mbedtls/platform_util.h"
#include "mbedtls/error.h"
#include <string.h>
#if defined(MBEDTLS_FS_IO)
#include <stdio.h>
#endif
#include "mbedtls/platform.h"
#define ENTROPY_MAX_LOOP 256 /**< Maximum amount to loop before error */
void mbedtls_entropy_init(mbedtls_entropy_context *ctx)
{
ctx->source_count = 0;
memset(ctx->source, 0, sizeof(ctx->source));
#if defined(MBEDTLS_THREADING_C)
mbedtls_mutex_init(&ctx->mutex);
#endif
ctx->accumulator_started = 0;
mbedtls_md_init(&ctx->accumulator);
/* Reminder: Update ENTROPY_HAVE_STRONG in the test files
* when adding more strong entropy sources here. */
#if !defined(MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES)
#if !defined(MBEDTLS_NO_PLATFORM_ENTROPY)
mbedtls_entropy_add_source(ctx, mbedtls_platform_entropy_poll, NULL,
MBEDTLS_ENTROPY_MIN_PLATFORM,
MBEDTLS_ENTROPY_SOURCE_STRONG);
#endif
#if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
mbedtls_entropy_add_source(ctx, mbedtls_hardware_poll, NULL,
MBEDTLS_ENTROPY_MIN_HARDWARE,
MBEDTLS_ENTROPY_SOURCE_STRONG);
#endif
#if defined(MBEDTLS_ENTROPY_NV_SEED)
mbedtls_entropy_add_source(ctx, mbedtls_nv_seed_poll, NULL,
MBEDTLS_ENTROPY_BLOCK_SIZE,
MBEDTLS_ENTROPY_SOURCE_STRONG);
ctx->initial_entropy_run = 0;
#endif
#endif /* MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES */
}
void mbedtls_entropy_free(mbedtls_entropy_context *ctx)
{
if (ctx == NULL) {
return;
}
/* If the context was already free, don't call free() again.
* This is important for mutexes which don't allow double-free. */
if (ctx->accumulator_started == -1) {
return;
}
#if defined(MBEDTLS_THREADING_C)
mbedtls_mutex_free(&ctx->mutex);
#endif
mbedtls_md_free(&ctx->accumulator);
#if defined(MBEDTLS_ENTROPY_NV_SEED)
ctx->initial_entropy_run = 0;
#endif
ctx->source_count = 0;
mbedtls_platform_zeroize(ctx->source, sizeof(ctx->source));
ctx->accumulator_started = -1;
}
int mbedtls_entropy_add_source(mbedtls_entropy_context *ctx,
mbedtls_entropy_f_source_ptr f_source, void *p_source,
size_t threshold, int strong)
{
int idx, ret = 0;
#if defined(MBEDTLS_THREADING_C)
if ((ret = mbedtls_mutex_lock(&ctx->mutex)) != 0) {
return ret;
}
#endif
idx = ctx->source_count;
if (idx >= MBEDTLS_ENTROPY_MAX_SOURCES) {
ret = MBEDTLS_ERR_ENTROPY_MAX_SOURCES;
goto exit;
}
ctx->source[idx].f_source = f_source;
ctx->source[idx].p_source = p_source;
ctx->source[idx].threshold = threshold;
ctx->source[idx].strong = strong;
ctx->source_count++;
exit:
#if defined(MBEDTLS_THREADING_C)
if (mbedtls_mutex_unlock(&ctx->mutex) != 0) {
return MBEDTLS_ERR_THREADING_MUTEX_ERROR;
}
#endif
return ret;
}
/*
* Entropy accumulator update
*/
static int entropy_update(mbedtls_entropy_context *ctx, unsigned char source_id,
const unsigned char *data, size_t len)
{
unsigned char header[2];
unsigned char tmp[MBEDTLS_ENTROPY_BLOCK_SIZE];
size_t use_len = len;
const unsigned char *p = data;
int ret = 0;
if (use_len > MBEDTLS_ENTROPY_BLOCK_SIZE) {
if ((ret = mbedtls_md(mbedtls_md_info_from_type(MBEDTLS_ENTROPY_MD),
data, len, tmp)) != 0) {
goto cleanup;
}
p = tmp;
use_len = MBEDTLS_ENTROPY_BLOCK_SIZE;
}
header[0] = source_id;
header[1] = use_len & 0xFF;
/*
* Start the accumulator if this has not already happened. Note that
* it is sufficient to start the accumulator here only because all calls to
* gather entropy eventually execute this code.
*/
if (ctx->accumulator_started == 0) {
ret = mbedtls_md_setup(&ctx->accumulator,
mbedtls_md_info_from_type(MBEDTLS_ENTROPY_MD), 0);
if (ret != 0) {
goto cleanup;
}
ret = mbedtls_md_starts(&ctx->accumulator);
if (ret != 0) {
goto cleanup;
}
ctx->accumulator_started = 1;
}
if ((ret = mbedtls_md_update(&ctx->accumulator, header, 2)) != 0) {
goto cleanup;
}
ret = mbedtls_md_update(&ctx->accumulator, p, use_len);
cleanup:
mbedtls_platform_zeroize(tmp, sizeof(tmp));
return ret;
}
int mbedtls_entropy_update_manual(mbedtls_entropy_context *ctx,
const unsigned char *data, size_t len)
{
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
#if defined(MBEDTLS_THREADING_C)
if ((ret = mbedtls_mutex_lock(&ctx->mutex)) != 0) {
return ret;
}
#endif
ret = entropy_update(ctx, MBEDTLS_ENTROPY_SOURCE_MANUAL, data, len);
#if defined(MBEDTLS_THREADING_C)
if (mbedtls_mutex_unlock(&ctx->mutex) != 0) {
return MBEDTLS_ERR_THREADING_MUTEX_ERROR;
}
#endif
return ret;
}
/*
* Run through the different sources to add entropy to our accumulator
*/
static int entropy_gather_internal(mbedtls_entropy_context *ctx)
{
int ret = MBEDTLS_ERR_ENTROPY_SOURCE_FAILED;
int i;
int have_one_strong = 0;
unsigned char buf[MBEDTLS_ENTROPY_MAX_GATHER];
size_t olen;
if (ctx->source_count == 0) {
return MBEDTLS_ERR_ENTROPY_NO_SOURCES_DEFINED;
}
/*
* Run through our entropy sources
*/
for (i = 0; i < ctx->source_count; i++) {
if (ctx->source[i].strong == MBEDTLS_ENTROPY_SOURCE_STRONG) {
have_one_strong = 1;
}
olen = 0;
if ((ret = ctx->source[i].f_source(ctx->source[i].p_source,
buf, MBEDTLS_ENTROPY_MAX_GATHER, &olen)) != 0) {
goto cleanup;
}
/*
* Add if we actually gathered something
*/
if (olen > 0) {
if ((ret = entropy_update(ctx, (unsigned char) i,
buf, olen)) != 0) {
return ret;
}
ctx->source[i].size += olen;
}
}
if (have_one_strong == 0) {
ret = MBEDTLS_ERR_ENTROPY_NO_STRONG_SOURCE;
}
cleanup:
mbedtls_platform_zeroize(buf, sizeof(buf));
return ret;
}
/*
* Thread-safe wrapper for entropy_gather_internal()
*/
int mbedtls_entropy_gather(mbedtls_entropy_context *ctx)
{
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
#if defined(MBEDTLS_THREADING_C)
if ((ret = mbedtls_mutex_lock(&ctx->mutex)) != 0) {
return ret;
}
#endif
ret = entropy_gather_internal(ctx);
#if defined(MBEDTLS_THREADING_C)
if (mbedtls_mutex_unlock(&ctx->mutex) != 0) {
return MBEDTLS_ERR_THREADING_MUTEX_ERROR;
}
#endif
return ret;
}
int mbedtls_entropy_func(void *data, unsigned char *output, size_t len)
{
int ret, count = 0, i, thresholds_reached;
size_t strong_size;
mbedtls_entropy_context *ctx = (mbedtls_entropy_context *) data;
unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE];
if (len > MBEDTLS_ENTROPY_BLOCK_SIZE) {
return MBEDTLS_ERR_ENTROPY_SOURCE_FAILED;
}
#if defined(MBEDTLS_ENTROPY_NV_SEED)
/* Update the NV entropy seed before generating any entropy for outside
* use.
*/
if (ctx->initial_entropy_run == 0) {
ctx->initial_entropy_run = 1;
if ((ret = mbedtls_entropy_update_nv_seed(ctx)) != 0) {
return ret;
}
}
#endif
#if defined(MBEDTLS_THREADING_C)
if ((ret = mbedtls_mutex_lock(&ctx->mutex)) != 0) {
return ret;
}
#endif
/*
* Always gather extra entropy before a call
*/
do {
if (count++ > ENTROPY_MAX_LOOP) {
ret = MBEDTLS_ERR_ENTROPY_SOURCE_FAILED;
goto exit;
}
if ((ret = entropy_gather_internal(ctx)) != 0) {
goto exit;
}
thresholds_reached = 1;
strong_size = 0;
for (i = 0; i < ctx->source_count; i++) {
if (ctx->source[i].size < ctx->source[i].threshold) {
thresholds_reached = 0;
}
if (ctx->source[i].strong == MBEDTLS_ENTROPY_SOURCE_STRONG) {
strong_size += ctx->source[i].size;
}
}
} while (!thresholds_reached || strong_size < MBEDTLS_ENTROPY_BLOCK_SIZE);
memset(buf, 0, MBEDTLS_ENTROPY_BLOCK_SIZE);
/*
* Note that at this stage it is assumed that the accumulator was started
* in a previous call to entropy_update(). If this is not guaranteed, the
* code below will fail.
*/
if ((ret = mbedtls_md_finish(&ctx->accumulator, buf)) != 0) {
goto exit;
}
/*
* Reset accumulator and counters and recycle existing entropy
*/
mbedtls_md_free(&ctx->accumulator);
mbedtls_md_init(&ctx->accumulator);
ret = mbedtls_md_setup(&ctx->accumulator,
mbedtls_md_info_from_type(MBEDTLS_ENTROPY_MD), 0);
if (ret != 0) {
goto exit;
}
ret = mbedtls_md_starts(&ctx->accumulator);
if (ret != 0) {
goto exit;
}
if ((ret = mbedtls_md_update(&ctx->accumulator, buf,
MBEDTLS_ENTROPY_BLOCK_SIZE)) != 0) {
goto exit;
}
/*
* Perform second hashing on entropy
*/
if ((ret = mbedtls_md(mbedtls_md_info_from_type(MBEDTLS_ENTROPY_MD),
buf, MBEDTLS_ENTROPY_BLOCK_SIZE, buf)) != 0) {
goto exit;
}
for (i = 0; i < ctx->source_count; i++) {
ctx->source[i].size = 0;
}
memcpy(output, buf, len);
ret = 0;
exit:
mbedtls_platform_zeroize(buf, sizeof(buf));
#if defined(MBEDTLS_THREADING_C)
if (mbedtls_mutex_unlock(&ctx->mutex) != 0) {
return MBEDTLS_ERR_THREADING_MUTEX_ERROR;
}
#endif
return ret;
}
#if defined(MBEDTLS_ENTROPY_NV_SEED)
int mbedtls_entropy_update_nv_seed(mbedtls_entropy_context *ctx)
{
int ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE];
/* Read new seed and write it to NV */
if ((ret = mbedtls_entropy_func(ctx, buf, MBEDTLS_ENTROPY_BLOCK_SIZE)) != 0) {
return ret;
}
if (mbedtls_nv_seed_write(buf, MBEDTLS_ENTROPY_BLOCK_SIZE) < 0) {
return MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
}
/* Manually update the remaining stream with a separator value to diverge */
memset(buf, 0, MBEDTLS_ENTROPY_BLOCK_SIZE);
ret = mbedtls_entropy_update_manual(ctx, buf, MBEDTLS_ENTROPY_BLOCK_SIZE);
return ret;
}
#endif /* MBEDTLS_ENTROPY_NV_SEED */
#if defined(MBEDTLS_FS_IO)
int mbedtls_entropy_write_seed_file(mbedtls_entropy_context *ctx, const char *path)
{
int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
FILE *f = NULL;
unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE];
if ((ret = mbedtls_entropy_func(ctx, buf, MBEDTLS_ENTROPY_BLOCK_SIZE)) != 0) {
ret = MBEDTLS_ERR_ENTROPY_SOURCE_FAILED;
goto exit;
}
if ((f = fopen(path, "wb")) == NULL) {
ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
goto exit;
}
/* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
mbedtls_setbuf(f, NULL);
if (fwrite(buf, 1, MBEDTLS_ENTROPY_BLOCK_SIZE, f) != MBEDTLS_ENTROPY_BLOCK_SIZE) {
ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
goto exit;
}
ret = 0;
exit:
mbedtls_platform_zeroize(buf, sizeof(buf));
if (f != NULL) {
fclose(f);
}
return ret;
}
int mbedtls_entropy_update_seed_file(mbedtls_entropy_context *ctx, const char *path)
{
int ret = 0;
FILE *f;
size_t n;
unsigned char buf[MBEDTLS_ENTROPY_MAX_SEED_SIZE];
if ((f = fopen(path, "rb")) == NULL) {
return MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
}
/* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
mbedtls_setbuf(f, NULL);
fseek(f, 0, SEEK_END);
n = (size_t) ftell(f);
fseek(f, 0, SEEK_SET);
if (n > MBEDTLS_ENTROPY_MAX_SEED_SIZE) {
n = MBEDTLS_ENTROPY_MAX_SEED_SIZE;
}
if (fread(buf, 1, n, f) != n) {
ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
} else {
ret = mbedtls_entropy_update_manual(ctx, buf, n);
}
fclose(f);
mbedtls_platform_zeroize(buf, sizeof(buf));
if (ret != 0) {
return ret;
}
return mbedtls_entropy_write_seed_file(ctx, path);
}
#endif /* MBEDTLS_FS_IO */
#if defined(MBEDTLS_SELF_TEST)
/*
* Dummy source function
*/
static int entropy_dummy_source(void *data, unsigned char *output,
size_t len, size_t *olen)
{
((void) data);
memset(output, 0x2a, len);
*olen = len;
return 0;
}
#if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
static int mbedtls_entropy_source_self_test_gather(unsigned char *buf, size_t buf_len)
{
int ret = 0;
size_t entropy_len = 0;
size_t olen = 0;
size_t attempts = buf_len;
while (attempts > 0 && entropy_len < buf_len) {
if ((ret = mbedtls_hardware_poll(NULL, buf + entropy_len,
buf_len - entropy_len, &olen)) != 0) {
return ret;
}
entropy_len += olen;
attempts--;
}
if (entropy_len < buf_len) {
ret = 1;
}
return ret;
}
static int mbedtls_entropy_source_self_test_check_bits(const unsigned char *buf,
size_t buf_len)
{
unsigned char set = 0xFF;
unsigned char unset = 0x00;
size_t i;
for (i = 0; i < buf_len; i++) {
set &= buf[i];
unset |= buf[i];
}
return set == 0xFF || unset == 0x00;
}
/*
* A test to ensure that the entropy sources are functioning correctly
* and there is no obvious failure. The test performs the following checks:
* - The entropy source is not providing only 0s (all bits unset) or 1s (all
* bits set).
* - The entropy source is not providing values in a pattern. Because the
* hardware could be providing data in an arbitrary length, this check polls
* the hardware entropy source twice and compares the result to ensure they
* are not equal.
* - The error code returned by the entropy source is not an error.
*/
int mbedtls_entropy_source_self_test(int verbose)
{
int ret = 0;
unsigned char buf0[2 * sizeof(unsigned long long int)];
unsigned char buf1[2 * sizeof(unsigned long long int)];
if (verbose != 0) {
mbedtls_printf(" ENTROPY_BIAS test: ");
}
memset(buf0, 0x00, sizeof(buf0));
memset(buf1, 0x00, sizeof(buf1));
if ((ret = mbedtls_entropy_source_self_test_gather(buf0, sizeof(buf0))) != 0) {
goto cleanup;
}
if ((ret = mbedtls_entropy_source_self_test_gather(buf1, sizeof(buf1))) != 0) {
goto cleanup;
}
/* Make sure that the returned values are not all 0 or 1 */
if ((ret = mbedtls_entropy_source_self_test_check_bits(buf0, sizeof(buf0))) != 0) {
goto cleanup;
}
if ((ret = mbedtls_entropy_source_self_test_check_bits(buf1, sizeof(buf1))) != 0) {
goto cleanup;
}
/* Make sure that the entropy source is not returning values in a
* pattern */
ret = memcmp(buf0, buf1, sizeof(buf0)) == 0;
cleanup:
if (verbose != 0) {
if (ret != 0) {
mbedtls_printf("failed\n");
} else {
mbedtls_printf("passed\n");
}
mbedtls_printf("\n");
}
return ret != 0;
}
#endif /* MBEDTLS_ENTROPY_HARDWARE_ALT */
/*
* The actual entropy quality is hard to test, but we can at least
* test that the functions don't cause errors and write the correct
* amount of data to buffers.
*/
int mbedtls_entropy_self_test(int verbose)
{
int ret = 1;
mbedtls_entropy_context ctx;
unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE] = { 0 };
unsigned char acc[MBEDTLS_ENTROPY_BLOCK_SIZE] = { 0 };
size_t i, j;
if (verbose != 0) {
mbedtls_printf(" ENTROPY test: ");
}
mbedtls_entropy_init(&ctx);
/* First do a gather to make sure we have default sources */
if ((ret = mbedtls_entropy_gather(&ctx)) != 0) {
goto cleanup;
}
ret = mbedtls_entropy_add_source(&ctx, entropy_dummy_source, NULL, 16,
MBEDTLS_ENTROPY_SOURCE_WEAK);
if (ret != 0) {
goto cleanup;
}
if ((ret = mbedtls_entropy_update_manual(&ctx, buf, sizeof(buf))) != 0) {
goto cleanup;
}
/*
* To test that mbedtls_entropy_func writes correct number of bytes:
* - use the whole buffer and rely on ASan to detect overruns
* - collect entropy 8 times and OR the result in an accumulator:
* any byte should then be 0 with probably 2^(-64), so requiring
* each of the 32 or 64 bytes to be non-zero has a false failure rate
* of at most 2^(-58) which is acceptable.
*/
for (i = 0; i < 8; i++) {
if ((ret = mbedtls_entropy_func(&ctx, buf, sizeof(buf))) != 0) {
goto cleanup;
}
for (j = 0; j < sizeof(buf); j++) {
acc[j] |= buf[j];
}
}
for (j = 0; j < sizeof(buf); j++) {
if (acc[j] == 0) {
ret = 1;
goto cleanup;
}
}
#if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
if ((ret = mbedtls_entropy_source_self_test(0)) != 0) {
goto cleanup;
}
#endif
cleanup:
mbedtls_entropy_free(&ctx);
if (verbose != 0) {
if (ret != 0) {
mbedtls_printf("failed\n");
} else {
mbedtls_printf("passed\n");
}
mbedtls_printf("\n");
}
return ret != 0;
}
#endif /* MBEDTLS_SELF_TEST */
#endif /* MBEDTLS_ENTROPY_C */
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