linux-kernel - Re: [PATCH v27 09/12] LRNG - add Jitter RNG fast noise source

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Date:   Thu, 9 Jan 2020 16:24:47 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Stephan Müller <smueller@...onox.de>,
        Arnd Bergmann <arnd@...db.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-crypto@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        linux-api@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Alexander E. Patrakov" <patrakov@...il.com>,
        "Ahmed S. Darwish" <darwish.07@...il.com>,
        "Theodore Y. Ts'o" <tytso@....edu>, Willy Tarreau <w@....eu>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        Vito Caputo <vcaputo@...garu.com>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jan Kara <jack@...e.cz>, Ray Strode <rstrode@...hat.com>,
        William Jon McCann <mccann@....edu>,
        zhangjs <zachary@...shancloud.com>,
        Andy Lutomirski <luto@...nel.org>,
        Florian Weimer <fweimer@...hat.com>,
        Lennart Poettering <mzxreary@...inter.de>,
        Nicolai Stange <nstange@...e.de>,
        "Peter, Matthias" <matthias.peter@....bund.de>,
        Marcelo Henrique Cerri <marcelo.cerri@...onical.com>,
        Roman Drahtmueller <draht@...altsekun.de>,
        Neil Horman <nhorman@...hat.com>,
        Julia Lawall <julia.lawall@...ia.fr>
Subject: Re: [PATCH v27 09/12] LRNG - add Jitter RNG fast noise source

Hi,

On 1/9/20 12:34 AM, Stephan Müller wrote:

> ---
>  drivers/char/lrng/Kconfig     | 11 +++++
>  drivers/char/lrng/Makefile    |  1 +
>  drivers/char/lrng/lrng_jent.c | 87 +++++++++++++++++++++++++++++++++++
>  3 files changed, 99 insertions(+)
>  create mode 100644 drivers/char/lrng/lrng_jent.c
> 

> diff --git a/drivers/char/lrng/lrng_jent.c b/drivers/char/lrng/lrng_jent.c
> new file mode 100644
> index 000000000000..97c0d192e9c8
> --- /dev/null
> +++ b/drivers/char/lrng/lrng_jent.c
> @@ -0,0 +1,87 @@
> +// SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
> +/*
> + * LRNG Fast Noise Source: Jitter RNG
> + *
> + * Copyright (C) 2016 - 2020, Stephan Mueller <smueller@...onox.de>
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/types.h>
> +#include <crypto/internal/jitterentropy.h>
> +
> +#include "lrng_internal.h"
> +
> +/*
> + * Estimated entropy of data is a 16th of LRNG_DRNG_SECURITY_STRENGTH_BITS.
> + * Albeit a full entropy assessment is provided for the noise source indicating
> + * that it provides high entropy rates and considering that it deactivates
> + * when it detects insufficient hardware, the chosen under estimation of
> + * entropy is considered to be acceptable to all reviewers.
> + */
> +static u32 jitterrng = LRNG_DRNG_SECURITY_STRENGTH_BITS>>4;
> +module_param(jitterrng, uint, 0644);
> +MODULE_PARM_DESC(jitterrng, "Entropy in bits of 256 data bits from Jitter "
> +			    "RNG noise source");
> +
> +/**
> + * Get Jitter RNG entropy
> + *
> + * @outbuf buffer to store entropy
> + * @outbuflen length of buffer
> + * @return > 0 on success where value provides the added entropy in bits
> + *	   0 if no fast source was available
> + */

Don't begin the comment block with /**
or convert it to Linux kernel-doc notation format.

> +static struct rand_data *lrng_jent_state;
> +
> +u32 lrng_get_jent(u8 *outbuf, unsigned int outbuflen)
> +{
> +	int ret;
> +	u32 ent_bits = jitterrng;
> +	unsigned long flags;
> +	static DEFINE_SPINLOCK(lrng_jent_lock);
> +	static int lrng_jent_initialized = 0;
> +
> +	spin_lock_irqsave(&lrng_jent_lock, flags);
> +
> +	if (!ent_bits || (lrng_jent_initialized == -1)) {
> +		spin_unlock_irqrestore(&lrng_jent_lock, flags);
> +		return 0;
> +	}
> +
> +	if (!lrng_jent_initialized) {
> +		lrng_jent_state = jent_lrng_entropy_collector();
> +		if (!lrng_jent_state) {
> +			jitterrng = 0;
> +			lrng_jent_initialized = -1;
> +			spin_unlock_irqrestore(&lrng_jent_lock, flags);
> +			pr_info("Jitter RNG unusable on current system\n");
> +			return 0;
> +		}
> +		lrng_jent_initialized = 1;
> +		pr_debug("Jitter RNG working on current system\n");
> +	}
> +	ret = jent_read_entropy(lrng_jent_state, outbuf, outbuflen);
> +	spin_unlock_irqrestore(&lrng_jent_lock, flags);
> +
> +	if (ret) {
> +		pr_debug("Jitter RNG failed with %d\n", ret);
> +		return 0;
> +	}
> +
> +	/* Obtain entropy statement */
> +	if (outbuflen != LRNG_DRNG_SECURITY_STRENGTH_BYTES)
> +		ent_bits = (ent_bits * outbuflen<<3) /
> +			   LRNG_DRNG_SECURITY_STRENGTH_BITS;
> +	/* Cap entropy to buffer size in bits */
> +	ent_bits = min_t(u32, ent_bits, outbuflen<<3);
> +	pr_debug("obtained %u bits of entropy from Jitter RNG noise source\n",
> +		 ent_bits);
> +
> +	return ent_bits;
> +}
> +
> +u32 lrng_jent_entropylevel(void)
> +{
> +	return min_t(u32, jitterrng, LRNG_DRNG_SECURITY_STRENGTH_BITS);
> +}
> 

thanks.
-- 
~Randy