linux-kernel - Re: [PATCH] Allow hwrng to initialize crng.

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Date:   Fri, 5 Oct 2018 09:45:57 +0800
From:   Louis Collard <louiscollard@...omium.org>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     linux-integrity@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, Andrey Pronin <apronin@...omium.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        "David R. Bild" <david.bild@...tum.com>,
        PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Michael Buesch <m@...s.ch>,
        Arvind Yadav <arvind.yadav.cs@...il.com>,
        Gary R Hook <gary.hook@....com>
Subject: Re: [PATCH] Allow hwrng to initialize crng.

On Wed, Sep 26, 2018 at 6:35 PM Jarkko Sakkinen
<jarkko.sakkinen@...ux.intel.com> wrote:
>
> On Wed, Sep 26, 2018 at 11:24:55AM +0800, Louis Collard wrote:
> > Some systems, for example embedded systems, do not generate
> > enough entropy on boot through interrupts, and boot may be blocked for
> > several minutes waiting for a call to getrandom to complete.
> >
> > Currently, random data is read from a hwrng when it is registered,
> > and is loaded into primary_crng. This data is treated in the same
> > way as data that is device-specific but otherwise unchanging, and
> > so primary_crng cannot become initialized with the data from the
> > hwrng.
> >
> > This change causes the data initially read from the hwrng to be
> > treated the same as subsequent data that is read from the hwrng if
> > it's quality score is non-zero.
> >
> > The implications of this are:
> >
> > The data read from hwrng can cause primary_crng to become
> > initialized, therefore avoiding problems of getrandom blocking
> > on boot.
> >
> > Calls to getrandom (with GRND_RANDOM) may be using entropy
> > exclusively (or in practise, almost exclusively) from the hwrng.
> >
> > Regarding the latter point; this behavior is the same as if a
> > user specified a quality score of 1 (bit of entropy per 1024 bits)
> > so hopefully this is not too scary a change to make.
> >
> > This change is the result of the discussion here:
> > https://patchwork.kernel.org/patch/10453893/
> >
> > Signed-off-by: Louis Collard <louiscollard@...omium.org>
>
> Acked-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
>
> /Jarkko

Thanks!

Adding a few people I think I should have included previously - I'm
new to this process so apologies for any missteps; please let me know
if there is anything else I can / should be doing!