git: a33ab3001a1e - stable/15 - random: Exclude the timestamp from healthtest for pure sources

The branch stable/15 has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=a33ab3001a1e6df38e4c974ea87a641c110cfbe3

commit a33ab3001a1e6df38e4c974ea87a641c110cfbe3
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2025-09-08 14:46:12 +0000
Commit:     Mark Johnston <markj@FreeBSD.org>
CommitDate: 2025-09-30 09:43:08 +0000

    random: Exclude the timestamp from healthtest for pure sources
    
    So-called pure sources provide entropy at regular intervals, so the
    timestamp counter provides little entropy.  Exclude it from health
    testing for such sources.
    
    Reviewed by:    cem, emaste
    MFC after:      2 weeks
    Sponsored by:   Stormshield
    Sponsored by:   Klara, Inc.
    Differential Revision:  https://reviews.freebsd.org/D52233
    
    (cherry picked from commit 480928ae657d81e41f8c10837cd1cf0ca87b14ae)
---
 sys/dev/random/random_harvestq.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/sys/dev/random/random_harvestq.c b/sys/dev/random/random_harvestq.c
index c308f6f80d59..2d7af254c52c 100644
--- a/sys/dev/random/random_harvestq.c
+++ b/sys/dev/random/random_harvestq.c
@@ -343,7 +343,17 @@ copy_event(uint32_t dst[static HARVESTSIZE + 1],
 {
 	memset(dst, 0, sizeof(uint32_t) * (HARVESTSIZE + 1));
 	memcpy(dst, event->he_entropy, event->he_size);
-	dst[HARVESTSIZE] = event->he_somecounter;
+	if (event->he_source <= RANDOM_ENVIRONMENTAL_END) {
+		/*
+		 * For pure entropy sources the timestamp counter is generally
+		 * quite determinstic since samples are taken at regular
+		 * intervals, so does not contribute much to the entropy.  To
+		 * make health tests more effective, exclude it from the sample,
+		 * since it might otherwise defeat the health tests in a
+		 * scenario where the source is stuck.
+		 */
+		dst[HARVESTSIZE] = event->he_somecounter;
+	}
 }
 
 static void