Linux Virtualization - Aug 2014 - [PATCH 1/2] rngd: add udev rule to source from hwrng if virtio-rng present

Hello,

I didn't find a mailing list for rng-tools, so CC'ing the kernel lists
and the last few committers.

The first patch in this series adds a udev rule to start rngd for
guests that have a virtio-rng device available.

The second patch attempts to add autoconf magic to install the udev
rule in the system dirs.  However, installing as non-root will
obviously fail.  Prefixes are also not honoured.  I don't know of a
better way, and we probably should leave this to distributions.
However, if someone has a better idea on how to expand this, please
suggest.


Amit Shah (2):
  rngd: add udev rule to source from hwrng if virtio-rng present
  Install udev rules in system-default directory

 90-virtio-rng.rules | 1 +
 Makefile.am         | 1 +
 configure.ac        | 8 ++++++++
 3 files changed, 10 insertions(+)
 create mode 100644 90-virtio-rng.rules

-- 
1.9.3

On KVM guests where the virtio-rng device is available, and set as the
current rng, this udev rule will start rngd which will feed in the
host-provided entropy to /dev/random.

Signed-off-by: Amit Shah <amit.shah at redhat.com>
---
 90-virtio-rng.rules | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 90-virtio-rng.rules

diff --git a/90-virtio-rng.rules b/90-virtio-rng.rules
new file mode 100644
index 0000000..07f2f9c
--- /dev/null
+++ b/90-virtio-rng.rules
@@ -0,0 +1 @@
+KERNEL=="hw_random", ATTR{rng_current}=="virtio*",
RUN+="/sbin/rngd -r /dev/hwrng"
-- 
1.9.3

not-quite-Signed-off-by: Amit Shah <amit.shah at redhat.com>
---
 Makefile.am  | 1 +
 configure.ac | 8 ++++++++
 2 files changed, 9 insertions(+)

diff --git a/Makefile.am b/Makefile.am
index f8490a3..a2b8173 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -8,6 +8,7 @@ sbin_PROGRAMS	 = rngd
 bin_PROGRAMS	 = rngtest
 man_MANS	 = rngd.8 rngtest.1
 noinst_LIBRARIES = librngd.a
+udevrules_DATA	 = 90-virtio-rng.rules
 
 rngd_SOURCES	= rngd.h rngd.c	rngd_entsource.h rngd_entsource.c	\
 		  rngd_linux.h rngd_linux.c util.c 			\
diff --git a/configure.ac b/configure.ac
index 27a2dba..4187aca 100644
--- a/configure.ac
+++ b/configure.ac
@@ -32,6 +32,14 @@ AC_ARG_WITH([libgcrypt],
 	[with_libgcrypt=check]
 )
 
+PKG_PROG_PKG_CONFIG
+
+AC_ARG_WITH([udevrulesdir],
+	AS_HELP_STRING([--with-udevrulesdir=DIR], [Directory for udev rules]),
+	[],
+	[with_udevrulesdir=$($PKG_CONFIG --variable=udevdir
udev)"/rules.d"])
+AC_SUBST([udevrulesdir], [$with_udevrulesdir])
+
 dnl Make sure anyone changing configure.ac/Makefile.am has a clue
 AM_MAINTAINER_MODE
 
-- 
1.9.3

On 08/07/2014 06:08 AM, Amit Shah wrote:
> On KVM guests where the virtio-rng device is available, and set as the
> current rng, this udev rule will start rngd which will feed in the
> host-provided entropy to /dev/random.
> 
> Signed-off-by: Amit Shah <amit.shah at redhat.com>
> ---
>  90-virtio-rng.rules | 1 +
>  1 file changed, 1 insertion(+)
>  create mode 100644 90-virtio-rng.rules
> 
> diff --git a/90-virtio-rng.rules b/90-virtio-rng.rules
> new file mode 100644
> index 0000000..07f2f9c
> --- /dev/null
> +++ b/90-virtio-rng.rules
> @@ -0,0 +1 @@
> +KERNEL=="hw_random", ATTR{rng_current}=="virtio*",
RUN+="/sbin/rngd -r /dev/hwrng"
> 
I'm not sure this is really right.  rngd can receive input from a number
of sources, and I suspect it would be better to rngd to be started much
earlier and perhaps get sent a SIGHUP to reconfigure when a hw_random
device appears ... not just the virtio one.

Currently rngd exits if there is no daemon.  There are a few ways to
deal with that: one is to run rngd on changes and leave a pid file
around; the rngd can try to signal the old rngd or launch itself;
another option would be to have a different rngd for each source.  To
some degree the above is obsolete when we get khwrngd widely deployed,
but that is a new-kernel-only kind of thing.

	-hpa