[Interest] [Development] QRandomGenerator and boot times
Sami Nurmenniemi
sami.nurmenniemi at qt.io
Mon Sep 18 10:44:31 CEST 2017
On 18/09/2017 7:59 pm, "Christian Gagneraud" <chgans at gmail.com
<mailto:chgans at gmail.com>> wrote:
>
>
>
> On 18/09/2017 7:34 pm, "Sami Nurmenniemi" <sami.nurmenniemi at qt.io
> <mailto:sami.nurmenniemi at qt.io>> wrote:
>
> On 15.09.2017 18:21, Thiago Macieira wrote:
>
> On Friday, 15 September 2017 00:31:36 PDT Sami Nurmenniemi
> wrote:
>
> I think we'll just have to accept blocking for the
> devices without
> hwrng. I don't know if we really support any such
> devices. If we do and
> boot time is essential for those, we'll have to figure
> out some way
> (probably saving entropy over reboot).
>
> And that would be a non-Qt job. I wasn't worried about Qt
> on real devices
> because I don't expect it to be run early enough to
> matter. On VMs, that's
> another story, and if you don't trust your
> undercloud-provided /dev/hwrng, why
> are you using that cloud? (Though I'll say there's an
> Intel team working on
> figuring out how a VM can get trust from the actual
> hardware, skipping the
> hypervisor trust)
>
> We have made some safety critical customer demos where fast
> boot time of Qt framework is essential. It was demoing boot
> time of 1.2s for a Qt application to start after powering on
> the device. I suppose that demo (and real safety critical use
> cases) is going to have problems with the QRandomGenerator
> even with hwrng in use.
>
>
>
> So basically, you have artificially "optimised" boot time by
> ignoring entropy management and now you're blaming
> QRandomGenerator. You can do one or the other, not both.
>
> Me too I can make a device boot in less than a second, but then
> don't be surprised if some features are missing/buggy....
>
> This sound very much like a beginner mistake, where boot time
> takes over functionality. Every one can boot an unfunctional
> device in less than a second. This is nothing new.
>
>
The point of mentioning the 1.2s demo was an answer to the statement "I
wasn't worried about Qt on real devices because I don't expect it to be
run early enough to matter." Maybe the demo application (being the only
user space process) needs to make the connection between hwrng + random
pool or preserve entropy over reboots.
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