[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH v3 1/3] VirtIO-RNG: Update default entropy sourc
From: |
Daniel P . Berrangé |
Subject: |
Re: [Qemu-devel] [PATCH v3 1/3] VirtIO-RNG: Update default entropy source to `/dev/urandom` |
Date: |
Fri, 10 May 2019 17:16:44 +0100 |
User-agent: |
Mutt/1.11.4 (2019-03-13) |
On Fri, May 10, 2019 at 12:12:41PM -0400, Michael S. Tsirkin wrote:
> On Fri, May 10, 2019 at 03:42:01PM +0200, Laurent Vivier wrote:
> > From: Kashyap Chamarthy <address@hidden>
> >
> > When QEMU exposes a VirtIO-RNG device to the guest, that device needs a
> > source of entropy, and that source needs to be "non-blocking", like
> > `/dev/urandom`. However, currently QEMU defaults to the problematic
> > `/dev/random`, which is "blocking" (as in, it waits until sufficient
> > entropy is available).
> >
> > Why prefer `/dev/urandom` over `/dev/random`?
> > ---------------------------------------------
> >
> > The man pages of urandom(4) and random(4) state:
> >
> > "The /dev/random device is a legacy interface which dates back to a
> > time where the cryptographic primitives used in the implementation
> > of /dev/urandom were not widely trusted. It will return random
> > bytes only within the estimated number of bits of fresh noise in the
> > entropy pool, blocking if necessary. /dev/random is suitable for
> > applications that need high quality randomness, and can afford
> > indeterminate delays."
> >
> > Further, the "Usage" section of the said man pages state:
> >
> > "The /dev/random interface is considered a legacy interface, and
> > /dev/urandom is preferred and sufficient in all use cases, with the
> > exception of applications which require randomness during early boot
> > time; for these applications, getrandom(2) must be used instead,
> > because it will block until the entropy pool is initialized.
>
> So how about just using getrandom then?
The 3rd patch in this series addresses that.
Regards,
Daniel
--
|: https://berrange.com -o- https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org -o- https://fstop138.berrange.com :|
|: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
Re: [Qemu-devel] [PATCH v3 1/3] VirtIO-RNG: Update default entropy source to `/dev/urandom`, Markus Armbruster, 2019/05/10
[Qemu-devel] [PATCH v3 2/3] rng-builtin: add an RNG backend that uses qemu_guest_getrandom(), Laurent Vivier, 2019/05/10
[Qemu-devel] [PATCH v3 3/3] virtio-rng: change default backend to rng-builtin, Laurent Vivier, 2019/05/10