From 9a56cf2b5b4970843c215091ea9823a67e077310 Mon Sep 17 00:00:00 2001
From: Leo Famulari <leo@famulari.name>
Date: Wed, 13 Dec 2017 18:49:28 -0500
Subject: [PATCH] services: urandom-seed: Try using a HWRNG to seed the Linux
CRNG at boot.
* gnu/services/base.scm (urandom-seed-shepherd-service): Try to read from
'/dev/hwrng' at boot, as a supplement to any saved random seed.
* doc/guix.texi (Base Services): Document the new feature.
---
doc/guix.texi | 4 +++-
gnu/services/base.scm | 18 ++++++++++++++++++
2 files changed, 21 insertions(+), 1 deletion(-)
diff --git a/doc/guix.texi b/doc/guix.texi
index 3bb29db9602..6b6f8dedae9 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -10025,7 +10025,9 @@ well as in the @var{groups} field of the @var{operating-system} record.
@deffn {Scheme Procedure} urandom-seed-service
Save some entropy in @var{%random-seed-file} to seed @file{/dev/urandom}
-when rebooting.
+when rebooting. It also tries to seed @file{/dev/urandom} from
+@file{/dev/hwrng} while booting, if @file{/dev/hwrng} exists and is
+readable.
@end deffn
@defvr {Scheme Variable} %random-seed-file
diff --git a/gnu/services/base.scm b/gnu/services/base.scm
index 5e08927af35..a3654fd4d32 100644
--- a/gnu/services/base.scm
+++ b/gnu/services/base.scm
@@ -516,6 +516,24 @@ (define (urandom-seed-shepherd-service _)
(call-with-output-file "/dev/urandom"
(lambda (urandom)
(dump-port seed urandom))))))
+
+ ;; Try writing from /dev/hwrng into /dev/urandom.
+ ;; It seems that the file /dev/hwrng always exists, even
+ ;; when there is no hardware random number generator
+ ;; available. So, we handle a failed read or any other error
+ ;; reported by the operating system.
+ (let ((buf (catch 'system-error
+ (lambda ()
+ (call-with-input-file "/dev/hwrng"
+ (lambda (hwrng)
+ (get-bytevector-n hwrng 512))))
+ ;; Silence is golden...
+ (const #f))))
+ (when buf
+ (call-with-output-file "/dev/urandom"
+ (lambda (urandom)
+ (put-bytevector urandom buf)))))
+
;; Immediately refresh the seed in case the system doesn't
;; shut down cleanly.
(call-with-input-file "/dev/urandom"
--
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