[Arm-dev] rng-tools missing and /dev/hwrng without driver

[Robert Moskowitz]

I find this very interesting point.  I have done a bit of research into 
entropy_avail and for example,

Cat /dev/random can empty it.  I went for > 2080 on my Cubieboard2 to 
Zero, it is now back up to 870.

On 04/17/2017 11:39 AM, SW at EU wrote:
> Hi,
>
> today I will report a problem that is released to ipa-server. This 
> server contains a certificate authority and such service need many 
> entropy. The default on CentOS 7 on a Banana PI is not enough, i.e. 
> $(cat /proc/sys/kernel/random/entropy_avail) is less than 1000.
>
> I have solved this in meantime by installing and enabling of haveged 
> from the EPEL repository. Normally it would be done by installing the 
> rng-tools. But there are two problems:
> 1. The rng-tools was not in the repositories, so I have 
> downloaded rng-tools-5-8.fc24.armv7hl.rpm because this are the same 
> version which is included in CentOS 7.3 for x86_64.

You can find the Centos rng-tools at:

https://armv7.dev.centos.org/repodir/c7-pass-1/rng-tools/5-2.el7/armv7hl/rng-tools-5-2.el7.armv7hl.rpm

Unfortunately, there are a lot of EPEL rpms that did not make it into 
the repo.

> 2. This rng-tools are usable but the daemon starts and stops 
> immediately with the following error message:
> # rngd -v
> /dev/hwrng: No such device
> /dev/tpm0: No such file or directory
> No entropy sources found, exiting

I now get:

# rngd -v
read error

read error

Available entropy sources:
         Intel/AMD hardware rng

Wow, entropy_avail is now up to 1052!  Looks like since I added 
rng-tools things are looking up.  I am going to add this to my howto...

>
> This is not the problem of this binary it is a problem of the Kernel. 
> /dev/hwrng exists and if I remove it then it reappears after reboot, but
>
> # ls -l /dev/hwrng
> crw-------. 1 root root 10, 183  1. Jan 1970  /dev/hwrng
>
> #  udevadm info -a -n /dev/hwrng
>
>
> Udevadm info starts with the device specified by the devpath and then
>
> walks up the chain of parent devices. It prints for every device
>
> found, all possible attributes in the udev rules key format.
>
> A rule to match, can be composed by the attributes of the device
>
> and the attributes from one single parent device.
>
>
>   looking at device '/devices/virtual/misc/hw_random':
>
>   KERNEL=="hw_random"
>
>   SUBSYSTEM=="misc"
>
>   DRIVER==""
>
>   ATTR{rng_current}=="none"
>
>   ATTR{rng_available}==""
>

I get the same results.  Try the Centos rng-tools and see if it makes a 
difference on your BPi.

>
> there is no driver for this device. I have searched and found this 
> link http://forum.lemaker.org/thread-23618-1-1.html which includes a 
> link to the full story. If I read all right then on bananian 
> /dev/hwrng appears only if the adapted or a more actual sun4i-ss.ko 
> module is loaded (there is written: "module author has indicated this 
> will be going into the mainline kernel shortly“). This module is also 
> loaded on a Banana PI with current CentOS 7. So does the kernel of 
> CentOS 7.3 for ARM32 include this patch and if yes why it does not 
> work or otherwise why this device appears but has no driver?
>
> TIA,
> Silvio
>
>
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>
>
>
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