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

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Date:   Wed, 26 Sep 2018 13:35:21 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Louis Collard <louiscollard@...omium.org>
Cc:     linux-integrity@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, apronin@...omium.org,
        Jason Gunthorpe <jgg@...pe.ca>, david.bild@...tum.com
Subject: Re: [PATCH] Allow hwrng to initialize crng.

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