diff options
Diffstat (limited to 'library/entropy.c')
| -rw-r--r-- | library/entropy.c | 676 |
1 files changed, 676 insertions, 0 deletions
diff --git a/library/entropy.c b/library/entropy.c new file mode 100644 index 00000000000..e3bc8516e2f --- /dev/null +++ b/library/entropy.c @@ -0,0 +1,676 @@ +/* + * 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 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 */ |