Message-ID: <559A5919.3060308@openwrt.org> (sfid-20150706_123205_907846_5411318E)
Date: Mon, 06 Jul 2015 12:31:53 +0200
From: Felix Fietkau <nbd@openwrt.org>
MIME-Version: 1.0
To: miaoqing@qti.qualcomm.com, linville@tuxdriver.com
CC: linux-wireless@vger.kernel.org, ath9k-devel@qca.qualcomm.com,
	kvalo@qca.qualcomm.com
Subject: Re: [PATCH v2] ath9k: export HW random number generator
References: <1435912110-9646-1-git-send-email-miaoqing@qca.qualcomm.com>
In-Reply-To: <1435912110-9646-1-git-send-email-miaoqing@qca.qualcomm.com>
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Sender: linux-wireless-owner@vger.kernel.org

On 2015-07-03 10:28, miaoqing@qti.qualcomm.com wrote:
> From: Miaoqing Pan <miaoqing@qca.qualcomm.com>
> 
> We measured the ADC-based entropy in 3 ways, Shannon entropy,
> collision entropy, and directly measured min-entropy. Entropy is
> in bits per 16 bit value,
>    ---------------------------
>    Shannon | collision | min
>    ---------------------------
>    12.00   | 10.80     | 9.18
>    ---------------------------
> 
> Recommend: A generous safety factor be used. NIST Special Publication
> 800-90B (draft) requires that data used to seed a deterministic random
> bit generator with N bits of strength have an estimated entropy at least
> twice the block size of the underlying primitive. Given all the
> uncertainties, it would be wise to collect even more.
> 
> Analysis was done by Jacobson,David(djacobso@qti.qualcomm.com).
> 
> Signed-off-by: Miaoqing Pan <miaoqing@qca.qualcomm.com>
> ---
>  drivers/net/wireless/ath/ath9k/Kconfig  |  7 ++++
>  drivers/net/wireless/ath/ath9k/Makefile |  1 +
>  drivers/net/wireless/ath/ath9k/ath9k.h  | 23 ++++++++++++
>  drivers/net/wireless/ath/ath9k/main.c   |  4 ++
>  drivers/net/wireless/ath/ath9k/rng.c    | 66 +++++++++++++++++++++++++++++++++
>  5 files changed, 101 insertions(+)
>  create mode 100644 drivers/net/wireless/ath/ath9k/rng.c
> 

> --- /dev/null
> +++ b/drivers/net/wireless/ath/ath9k/rng.c
> @@ -0,0 +1,66 @@
> +/*
> + * Copyright (c) 2015 Qualcomm Atheros, Inc.
> + *
> + * Permission to use, copy, modify, and/or distribute this software for any
> + * purpose with or without fee is hereby granted, provided that the above
> + * copyright notice and this permission notice appear in all copies.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
> + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
> + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
> + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
> + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
> + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
> + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
> + */
> +
> +#include "ath9k.h"
> +#include "hw.h"
> +#include "ar9003_phy.h"
> +
> +static int ath9k_rng_data_read(struct hwrng *rng, u32 *data)
> +{
> +	u32 v1, v2;
> +	struct ath_softc *sc = (struct ath_softc *)rng->priv;
> +	struct ath_hw *ah = sc->sc_ah;
> +
> +	ath9k_ps_wakeup(sc);
> +
> +	v1 = REG_READ(ah, AR_PHY_TST_ADC);
> +	v2 = REG_READ(ah, AR_PHY_TST_ADC);
> +
> +	ath9k_ps_restore(sc);
> +
> +	/* wait for data ready */
> +	if (v1 && v2 && sc->rng_last != v1 && v1 != v2) {
> +		*data = (v1 & 0xffff) | (v2 << 16);
> +		sc->rng_last = v2;
> +
> +		return sizeof(u32);
> +	}
I have some doubt about this part. Doesn't the value of AR_PHY_TST_ADC
depend on the initialization of the baseband observation registers?
What guarantee is there that it's initialized to return any data that is
useful for random number generation on all chipsets?
Did you validate all relevant initval settings for this?

- Felix