linux-kernel - Re: [PATCH] crypto: sun4i-ss: support the Security System PRNG

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Date:   Tue, 18 Oct 2016 16:24:22 +0200
From:   Stephan Mueller <smueller@...onox.de>
To:     Corentin Labbe <clabbe.montjoie@...il.com>
Cc:     herbert@...dor.apana.org.au, davem@...emloft.net,
        maxime.ripard@...e-electrons.com, wens@...e.org,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] crypto: sun4i-ss: support the Security System PRNG

Am Dienstag, 18. Oktober 2016, 14:34:27 CEST schrieb Corentin Labbe:

Hi Corentin,

> diff --git a/drivers/crypto/sunxi-ss/sun4i-ss-hwrng.c
> b/drivers/crypto/sunxi-ss/sun4i-ss-hwrng.c new file mode 100644
> index 0000000..95fadb7
> --- /dev/null
> +++ b/drivers/crypto/sunxi-ss/sun4i-ss-hwrng.c
> @@ -0,0 +1,70 @@
> +#include "sun4i-ss.h"
> +
> +static int sun4i_ss_hwrng_init(struct hwrng *hwrng)
> +{
> +	struct sun4i_ss_ctx *ss;
> +
> +	ss = container_of(hwrng, struct sun4i_ss_ctx, hwrng);
> +	get_random_bytes(ss->seed, SS_SEED_LEN);

Is it wise to call get_random_bytes once in the init function and never 
thereafter?

This init function may be called during boot time of the kernel at which the 
input_pool may not yet have received sufficient amounts of entropy.

What about registering a callback with add_random_ready_callback and seed 
again when sufficient entropy was collected?

Ciao
Stephan