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diff --git a/sys/dev/random/random_harvestq.c b/sys/dev/random/random_harvestq.c
--- a/sys/dev/random/random_harvestq.c
+++ b/sys/dev/random/random_harvestq.c
@@ -464,7 +464,7 @@
"Enable NIST SP 800-90B health tests for noise sources");
static void
-random_healthtest_init(enum random_entropy_source source)
+random_healthtest_init(enum random_entropy_source source, int min_entropy)
{
struct health_test_softc *ht;
@@ -485,20 +485,52 @@
}
/*
- * Set cutoff values for the two tests, assuming that each sample has
- * min-entropy of 1 bit and allowing for an error rate of 1 in 2^{34}.
- * With a sample rate of RANDOM_KTHREAD_HZ, we expect to see an false
- * positive once in ~54.5 years.
+ * Set cutoff values for the two tests, given a min-entropy estimate for
+ * the source and allowing for an error rate of 1 in 2^{34}. With a
+ * min-entropy estimate of 1 bit and a sample rate of RANDOM_KTHREAD_HZ,
+ * we expect to see an false positive once in ~54.5 years.
*
* The RCT limit comes from the formula in section 4.4.1.
*
- * The APT cutoff is calculated using the formula in section 4.4.2
+ * The APT cutoffs are calculated using the formula in section 4.4.2
* footnote 10 with the number of Bernoulli trials changed from W to
* W-1, since the test as written counts the number of samples equal to
- * the first sample in the window, and thus tests W-1 samples.
+ * the first sample in the window, and thus tests W-1 samples. We
+ * provide cutoffs for estimates up to sizeof(uint32_t)*HARVESTSIZE*8
+ * bits.
*/
- ht->ht_rct_limit = 35;
- ht->ht_apt_cutoff = 330;
+ const int apt_cutoffs[] = {
+ [1] = 329,
+ [2] = 195,
+ [3] = 118,
+ [4] = 73,
+ [5] = 48,
+ [6] = 33,
+ [7] = 23,
+ [8] = 17,
+ [9] = 13,
+ [10] = 11,
+ [11] = 9,
+ [12] = 8,
+ [13] = 7,
+ [14] = 6,
+ [15] = 5,
+ [16] = 5,
+ [17 ... 19] = 4,
+ [20 ... 25] = 3,
+ [26 ... 42] = 2,
+ [43 ... 64] = 1,
+ };
+ const int error_rate = 34;
+
+ if (min_entropy == 0)
+ min_entropy = 1;
+ else if (min_entropy < 0 || min_entropy >= nitems(apt_cutoffs)) {
+ panic("invalid min_entropy %d for %s", min_entropy,
+ random_source_descr[source]);
+ }
+ ht->ht_rct_limit = 1 + howmany(error_rate, min_entropy);
+ ht->ht_apt_cutoff = apt_cutoffs[min_entropy];
}
static int
@@ -652,8 +684,12 @@
RANDOM_HARVEST_INIT_LOCK();
harvest_context.hc_active_buf = 0;
- for (int i = 0; i < ENTROPYSOURCE; i++)
- random_healthtest_init(i);
+ for (int i = 0; i < ENTROPYSOURCE; i++) {
+ int min_entropy;
+
+ min_entropy = 0;
+ random_healthtest_init(i, min_entropy);
+ }
}
SYSINIT(random_device_h_init, SI_SUB_RANDOM, SI_ORDER_THIRD, random_harvestq_init, NULL);

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