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crypto: jitter - add RCT/APT support for different OSRs
The oversampling rate (OSR) value specifies the heuristically implied entropy in the recorded data - H_submitter = 1/osr. A different entropy estimate implies a different APT/RCT cutoff value. This change adds support for OSRs 1 through 15. This OSR can be selected by the caller of the Jitter RNG. For this patch, the caller still uses one hard-coded OSR. A subsequent patch allows this value to be configured. In addition, the power-up self test is adjusted as follows: * It allows the caller to provide an oversampling rate that should be tested with - commonly it should be the same as used for the actual runtime operation. This makes the power-up testing therefore consistent with the runtime operation. * It calls now jent_measure_jitter (i.e. collects the full entropy that can possibly be harvested by the Jitter RNG) instead of only jent_condition_data (which only returns the entropy harvested from the conditioning component). This should now alleviate reports where the Jitter RNG initialization thinks there is too little entropy. * The power-up test now solely relies on the (enhanced) APT and RCT test that is used as a health test at runtime. The code allowing the different OSRs as well as the power-up test changes are present in the user space version of the Jitter RNG 3.4.1 and thus was already in production use for some time. Reported-by "Ospan, Abylay" <aospan@amazon.com> Signed-off-by: Stephan Mueller <smueller@chronox.de> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Stephan Müller
Herbert Xu
parent
7b8c6aee0d
commit
04597c8dd6
3 changed files with 122 additions and 116 deletions
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@ -245,7 +245,7 @@ static int jent_kcapi_init(struct crypto_tfm *tfm)
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crypto_shash_init(sdesc);
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rng->sdesc = sdesc;
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rng->entropy_collector = jent_entropy_collector_alloc(1, 0, sdesc);
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rng->entropy_collector = jent_entropy_collector_alloc(0, 0, sdesc);
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if (!rng->entropy_collector) {
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ret = -ENOMEM;
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goto err;
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@ -334,7 +334,7 @@ static int __init jent_mod_init(void)
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desc->tfm = tfm;
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crypto_shash_init(desc);
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ret = jent_entropy_init(desc);
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ret = jent_entropy_init(0, 0, desc);
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shash_desc_zero(desc);
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crypto_free_shash(tfm);
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if (ret) {
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@ -72,6 +72,8 @@ struct rand_data {
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__u64 prev_time; /* SENSITIVE Previous time stamp */
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__u64 last_delta; /* SENSITIVE stuck test */
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__s64 last_delta2; /* SENSITIVE stuck test */
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unsigned int flags; /* Flags used to initialize */
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unsigned int osr; /* Oversample rate */
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#define JENT_MEMORY_BLOCKS 64
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#define JENT_MEMORY_BLOCKSIZE 32
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@ -88,16 +90,9 @@ struct rand_data {
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/* Repetition Count Test */
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unsigned int rct_count; /* Number of stuck values */
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/* Intermittent health test failure threshold of 2^-30 */
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/* From an SP800-90B perspective, this RCT cutoff value is equal to 31. */
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/* However, our RCT implementation starts at 1, so we subtract 1 here. */
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#define JENT_RCT_CUTOFF (31 - 1) /* Taken from SP800-90B sec 4.4.1 */
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#define JENT_APT_CUTOFF 325 /* Taken from SP800-90B sec 4.4.2 */
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/* Permanent health test failure threshold of 2^-60 */
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/* From an SP800-90B perspective, this RCT cutoff value is equal to 61. */
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/* However, our RCT implementation starts at 1, so we subtract 1 here. */
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#define JENT_RCT_CUTOFF_PERMANENT (61 - 1)
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#define JENT_APT_CUTOFF_PERMANENT 355
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/* Adaptive Proportion Test cutoff values */
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unsigned int apt_cutoff; /* Intermittent health test failure */
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unsigned int apt_cutoff_permanent; /* Permanent health test failure */
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#define JENT_APT_WINDOW_SIZE 512 /* Data window size */
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/* LSB of time stamp to process */
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#define JENT_APT_LSB 16
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@ -122,6 +117,9 @@ struct rand_data {
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* zero). */
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#define JENT_ESTUCK 8 /* Too many stuck results during init. */
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#define JENT_EHEALTH 9 /* Health test failed during initialization */
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#define JENT_ERCT 10 /* RCT failed during initialization */
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#define JENT_EHASH 11 /* Hash self test failed */
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#define JENT_EMEM 12 /* Can't allocate memory for initialization */
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/*
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* The output n bits can receive more than n bits of min entropy, of course,
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@ -147,6 +145,48 @@ struct rand_data {
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* This test complies with SP800-90B section 4.4.2.
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***************************************************************************/
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/*
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* See the SP 800-90B comment #10b for the corrected cutoff for the SP 800-90B
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* APT.
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* http://www.untruth.org/~josh/sp80090b/UL%20SP800-90B-final%20comments%20v1.9%2020191212.pdf
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* In in the syntax of R, this is C = 2 + qbinom(1 − 2^(−30), 511, 2^(-1/osr)).
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* (The original formula wasn't correct because the first symbol must
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* necessarily have been observed, so there is no chance of observing 0 of these
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* symbols.)
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*
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* For the alpha < 2^-53, R cannot be used as it uses a float data type without
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* arbitrary precision. A SageMath script is used to calculate those cutoff
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* values.
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*
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* For any value above 14, this yields the maximal allowable value of 512
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* (by FIPS 140-2 IG 7.19 Resolution # 16, we cannot choose a cutoff value that
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* renders the test unable to fail).
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*/
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static const unsigned int jent_apt_cutoff_lookup[15] = {
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325, 422, 459, 477, 488, 494, 499, 502,
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505, 507, 508, 509, 510, 511, 512 };
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static const unsigned int jent_apt_cutoff_permanent_lookup[15] = {
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355, 447, 479, 494, 502, 507, 510, 512,
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512, 512, 512, 512, 512, 512, 512 };
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#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
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static void jent_apt_init(struct rand_data *ec, unsigned int osr)
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{
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/*
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* Establish the apt_cutoff based on the presumed entropy rate of
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* 1/osr.
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*/
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if (osr >= ARRAY_SIZE(jent_apt_cutoff_lookup)) {
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ec->apt_cutoff = jent_apt_cutoff_lookup[
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ARRAY_SIZE(jent_apt_cutoff_lookup) - 1];
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ec->apt_cutoff_permanent = jent_apt_cutoff_permanent_lookup[
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ARRAY_SIZE(jent_apt_cutoff_permanent_lookup) - 1];
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} else {
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ec->apt_cutoff = jent_apt_cutoff_lookup[osr - 1];
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ec->apt_cutoff_permanent =
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jent_apt_cutoff_permanent_lookup[osr - 1];
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}
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}
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/*
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* Reset the APT counter
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*
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@ -187,12 +227,12 @@ static void jent_apt_insert(struct rand_data *ec, unsigned int delta_masked)
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/* APT health test failure detection */
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static int jent_apt_permanent_failure(struct rand_data *ec)
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{
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return (ec->apt_count >= JENT_APT_CUTOFF_PERMANENT) ? 1 : 0;
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return (ec->apt_count >= ec->apt_cutoff_permanent) ? 1 : 0;
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}
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static int jent_apt_failure(struct rand_data *ec)
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{
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return (ec->apt_count >= JENT_APT_CUTOFF) ? 1 : 0;
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return (ec->apt_count >= ec->apt_cutoff) ? 1 : 0;
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}
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/***************************************************************************
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@ -275,15 +315,28 @@ static int jent_stuck(struct rand_data *ec, __u64 current_delta)
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return 0;
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}
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/* RCT health test failure detection */
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/*
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* The cutoff value is based on the following consideration:
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* alpha = 2^-30 or 2^-60 as recommended in SP800-90B.
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* In addition, we require an entropy value H of 1/osr as this is the minimum
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* entropy required to provide full entropy.
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* Note, we collect (DATA_SIZE_BITS + ENTROPY_SAFETY_FACTOR)*osr deltas for
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* inserting them into the entropy pool which should then have (close to)
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* DATA_SIZE_BITS bits of entropy in the conditioned output.
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*
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* Note, ec->rct_count (which equals to value B in the pseudo code of SP800-90B
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* section 4.4.1) starts with zero. Hence we need to subtract one from the
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* cutoff value as calculated following SP800-90B. Thus
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* C = ceil(-log_2(alpha)/H) = 30*osr or 60*osr.
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*/
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static int jent_rct_permanent_failure(struct rand_data *ec)
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{
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return (ec->rct_count >= JENT_RCT_CUTOFF_PERMANENT) ? 1 : 0;
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return (ec->rct_count >= (60 * ec->osr)) ? 1 : 0;
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}
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static int jent_rct_failure(struct rand_data *ec)
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{
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return (ec->rct_count >= JENT_RCT_CUTOFF) ? 1 : 0;
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return (ec->rct_count >= (30 * ec->osr)) ? 1 : 0;
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}
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/* Report of health test failures */
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@ -448,7 +501,7 @@ static void jent_memaccess(struct rand_data *ec, __u64 loop_cnt)
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*
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* @return result of stuck test
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*/
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static int jent_measure_jitter(struct rand_data *ec)
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static int jent_measure_jitter(struct rand_data *ec, __u64 *ret_current_delta)
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{
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__u64 time = 0;
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__u64 current_delta = 0;
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@ -472,6 +525,10 @@ static int jent_measure_jitter(struct rand_data *ec)
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if (jent_condition_data(ec, current_delta, stuck))
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stuck = 1;
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/* return the raw entropy value */
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if (ret_current_delta)
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*ret_current_delta = current_delta;
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return stuck;
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}
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@ -489,11 +546,11 @@ static void jent_gen_entropy(struct rand_data *ec)
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safety_factor = JENT_ENTROPY_SAFETY_FACTOR;
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/* priming of the ->prev_time value */
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jent_measure_jitter(ec);
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jent_measure_jitter(ec, NULL);
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while (!jent_health_failure(ec)) {
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/* If a stuck measurement is received, repeat measurement */
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if (jent_measure_jitter(ec))
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if (jent_measure_jitter(ec, NULL))
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continue;
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/*
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@ -554,7 +611,8 @@ int jent_read_entropy(struct rand_data *ec, unsigned char *data,
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* Perform startup health tests and return permanent
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* error if it fails.
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*/
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if (jent_entropy_init(ec->hash_state))
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if (jent_entropy_init(ec->osr, ec->flags,
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ec->hash_state))
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return -3;
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return -2;
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@ -604,11 +662,15 @@ struct rand_data *jent_entropy_collector_alloc(unsigned int osr,
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/* verify and set the oversampling rate */
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if (osr == 0)
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osr = 1; /* minimum sampling rate is 1 */
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osr = 1; /* H_submitter = 1 / osr */
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entropy_collector->osr = osr;
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entropy_collector->flags = flags;
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entropy_collector->hash_state = hash_state;
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/* Initialize the APT */
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jent_apt_init(entropy_collector, osr);
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/* fill the data pad with non-zero values */
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jent_gen_entropy(entropy_collector);
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@ -622,20 +684,14 @@ void jent_entropy_collector_free(struct rand_data *entropy_collector)
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jent_zfree(entropy_collector);
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}
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int jent_entropy_init(void *hash_state)
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int jent_entropy_init(unsigned int osr, unsigned int flags, void *hash_state)
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{
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int i;
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__u64 delta_sum = 0;
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__u64 old_delta = 0;
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unsigned int nonstuck = 0;
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int time_backwards = 0;
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int count_mod = 0;
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int count_stuck = 0;
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struct rand_data ec = { 0 };
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struct rand_data *ec;
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int i, time_backwards = 0, ret = 0;
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/* Required for RCT */
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ec.osr = 1;
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ec.hash_state = hash_state;
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ec = jent_entropy_collector_alloc(osr, flags, hash_state);
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if (!ec)
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return JENT_EMEM;
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/* We could perform statistical tests here, but the problem is
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* that we only have a few loop counts to do testing. These
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@ -664,31 +720,28 @@ int jent_entropy_init(void *hash_state)
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#define TESTLOOPCOUNT 1024
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#define CLEARCACHE 100
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for (i = 0; (TESTLOOPCOUNT + CLEARCACHE) > i; i++) {
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__u64 time = 0;
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__u64 time2 = 0;
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__u64 delta = 0;
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unsigned int lowdelta = 0;
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int stuck;
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__u64 start_time = 0, end_time = 0, delta = 0;
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/* Invoke core entropy collection logic */
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jent_get_nstime(&time);
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ec.prev_time = time;
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jent_condition_data(&ec, time, 0);
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jent_get_nstime(&time2);
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jent_measure_jitter(ec, &delta);
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end_time = ec->prev_time;
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start_time = ec->prev_time - delta;
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/* test whether timer works */
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if (!time || !time2)
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return JENT_ENOTIME;
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delta = jent_delta(time, time2);
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if (!start_time || !end_time) {
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ret = JENT_ENOTIME;
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goto out;
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}
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/*
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* test whether timer is fine grained enough to provide
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* delta even when called shortly after each other -- this
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* implies that we also have a high resolution timer
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*/
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if (!delta)
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return JENT_ECOARSETIME;
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stuck = jent_stuck(&ec, delta);
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if (!delta || (end_time == start_time)) {
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ret = JENT_ECOARSETIME;
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goto out;
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}
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/*
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* up to here we did not modify any variable that will be
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@ -700,49 +753,9 @@ int jent_entropy_init(void *hash_state)
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if (i < CLEARCACHE)
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continue;
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if (stuck)
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count_stuck++;
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else {
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nonstuck++;
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/*
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* Ensure that the APT succeeded.
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*
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* With the check below that count_stuck must be less
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* than 10% of the overall generated raw entropy values
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* it is guaranteed that the APT is invoked at
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* floor((TESTLOOPCOUNT * 0.9) / 64) == 14 times.
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*/
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if ((nonstuck % JENT_APT_WINDOW_SIZE) == 0) {
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jent_apt_reset(&ec,
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delta & JENT_APT_WORD_MASK);
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}
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}
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/* Validate health test result */
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if (jent_health_failure(&ec))
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return JENT_EHEALTH;
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/* test whether we have an increasing timer */
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if (!(time2 > time))
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if (!(end_time > start_time))
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time_backwards++;
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/* use 32 bit value to ensure compilation on 32 bit arches */
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lowdelta = time2 - time;
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if (!(lowdelta % 100))
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count_mod++;
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/*
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* ensure that we have a varying delta timer which is necessary
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* for the calculation of entropy -- perform this check
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* only after the first loop is executed as we need to prime
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* the old_data value
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*/
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if (delta > old_delta)
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delta_sum += (delta - old_delta);
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else
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delta_sum += (old_delta - delta);
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old_delta = delta;
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}
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/*
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@ -752,31 +765,23 @@ int jent_entropy_init(void *hash_state)
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* should not fail. The value of 3 should cover the NTP case being
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* performed during our test run.
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*/
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if (time_backwards > 3)
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return JENT_ENOMONOTONIC;
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if (time_backwards > 3) {
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ret = JENT_ENOMONOTONIC;
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goto out;
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}
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/*
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* Variations of deltas of time must on average be larger
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* than 1 to ensure the entropy estimation
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* implied with 1 is preserved
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*/
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if ((delta_sum) <= 1)
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return JENT_EVARVAR;
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/* Did we encounter a health test failure? */
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if (jent_rct_failure(ec)) {
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ret = JENT_ERCT;
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goto out;
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}
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if (jent_apt_failure(ec)) {
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ret = JENT_EHEALTH;
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goto out;
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}
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/*
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* Ensure that we have variations in the time stamp below 10 for at
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* least 10% of all checks -- on some platforms, the counter increments
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* in multiples of 100, but not always
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*/
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if ((TESTLOOPCOUNT/10 * 9) < count_mod)
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return JENT_ECOARSETIME;
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out:
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jent_entropy_collector_free(ec);
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/*
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* If we have more than 90% stuck results, then this Jitter RNG is
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* likely to not work well.
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*/
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if ((TESTLOOPCOUNT/10 * 9) < count_stuck)
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return JENT_ESTUCK;
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return 0;
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return ret;
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}
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@ -9,7 +9,8 @@ extern int jent_hash_time(void *hash_state, __u64 time, u8 *addtl,
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int jent_read_random_block(void *hash_state, char *dst, unsigned int dst_len);
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struct rand_data;
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extern int jent_entropy_init(void *hash_state);
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extern int jent_entropy_init(unsigned int osr, unsigned int flags,
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void *hash_state);
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extern int jent_read_entropy(struct rand_data *ec, unsigned char *data,
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unsigned int len);
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