Re: [Qemu-devel] [PATCH v3 1/3] VirtIO-RNG: Update default entropy source to `/dev/urandom`

[Michael S. Tsirkin]

On Fri, May 10, 2019 at 05:16:44PM +0100, Daniel P. Berrangé wrote:
> 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.

It seems to use qemu_guest_getrandom which in turn
with patch 1 calls /dev/urandom...
Did I miss something?

> 
> Regards,
> Daniel
> -- 
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