Date: Mon, 21 Feb 2022 08:07:44 GMT From: "David E. O'Brien" <obrien@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: c91dd7ea7cd7 - stable/12 - random(4): Don't complain noisily when an entropy source is slow Message-ID: <202202210807.21L87iiZ036968@gitrepo.freebsd.org>
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The branch stable/12 has been updated by obrien: URL: https://cgit.FreeBSD.org/src/commit/?id=c91dd7ea7cd70b6b42693a3acb987173c63ec5bb commit c91dd7ea7cd70b6b42693a3acb987173c63ec5bb Author: Conrad Meyer <cem@FreeBSD.org> AuthorDate: 2019-05-08 14:54:32 +0000 Commit: David E. O'Brien <obrien@FreeBSD.org> CommitDate: 2022-02-21 05:56:42 +0000 random(4): Don't complain noisily when an entropy source is slow Mjg@ reports that RDSEED (r347239) causes a lot of logspam from this printf, and I don't feel that it is especially useful (even ratelimited). There are many other quality/quantity checks we're not performing on entropy sources; lack of high frequency availability does not disqualify a good entropy source. There is some discussion in the linked Differential about what logging might be appropriate and/or polling policy for slower TRNG sources. Please feel free to chime in if you have opinions. (cherry picked from commit e01ada5c44c66db8e1f7ed2c1f5622a794a1c43b) --- sys/dev/random/random_harvestq.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) diff --git a/sys/dev/random/random_harvestq.c b/sys/dev/random/random_harvestq.c index d98730d0054f..bb9ec5e4cea0 100644 --- a/sys/dev/random/random_harvestq.c +++ b/sys/dev/random/random_harvestq.c @@ -254,15 +254,19 @@ random_sources_feed(void) for (i = 0; i < npools; i++) { n = rrs->rrs_source->rs_read(entropy, sizeof(entropy)); KASSERT((n <= sizeof(entropy)), ("%s: rs_read returned too much data (%u > %zu)", __func__, n, sizeof(entropy))); - /* It would appear that in some circumstances (e.g. virtualisation), - * the underlying hardware entropy source might not always return - * random numbers. Accept this but make a noise. If too much happens, - * can that source be trusted? + /* + * Sometimes the HW entropy source doesn't have anything + * ready for us. This isn't necessarily untrustworthy. + * We don't perform any other verification of an entropy + * source (i.e., length is allowed to be anywhere from 1 + * to sizeof(entropy), quality is unchecked, etc), so + * don't balk verbosely at slow random sources either. + * There are reports that RDSEED on x86 metal falls + * behind the rate at which we query it, for example. + * But it's still a better entropy source than RDRAND. */ - if (n == 0) { - printf("%s: rs_read for hardware device '%s' returned no entropy.\n", __func__, rrs->rrs_source->rs_ident); + if (n == 0) continue; - } random_harvest_direct(entropy, n, rrs->rrs_source->rs_source); } }
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