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From:   Horia Geanta <horia.geanta@nxp.com>
To:     Andrey Smirnov <andrew.smirnov@gmail.com>,
        "linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>
CC:     Chris Healy <cphealy@gmail.com>,
        Lucas Stach <l.stach@pengutronix.de>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Iuliana Prodan <iuliana.prodan@nxp.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        dl-linux-imx <linux-imx@nxp.com>
Subject: Re: [PATCH v4 2/6] crypto: caam - enable prediction resistance in
 HRWNG
Thread-Topic: [PATCH v4 2/6] crypto: caam - enable prediction resistance in
 HRWNG
Thread-Index: AQHVoIQyJHCMNObN7kuHGNWFUpD0kQ==
Date:   Tue, 26 Nov 2019 09:13:38 +0000
Message-ID: <VI1PR0402MB348521C01FBACF44C531C7CD98450@VI1PR0402MB3485.eurprd04.prod.outlook.com>
References: <20191121155554.1227-1-andrew.smirnov@gmail.com>
 <20191121155554.1227-3-andrew.smirnov@gmail.com>
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On 11/21/2019 5:56 PM, Andrey Smirnov wrote:=0A=
> Instantiate CAAM RNG with prediction resistance enabled to improve its=0A=
> quality.=0A=
> =0A=
It's worth noting there are two RNG operations being changed:=0A=
-instantiation=0A=
-generation=0A=
=0A=
Generation with prediction resistance (PR) is only supported on=0A=
RNG state handles instantiated with PR option.=0A=
=0A=
Using PR when generating randomness effectively forces a reseed=0A=
of the DRBG / PRNG - that's how quality is improved.=0A=
=0A=
> diff --git a/drivers/crypto/caam/caamrng.c b/drivers/crypto/caam/caamrng.=
c=0A=
> index e8baacaabe07..6dde8ae3cd9b 100644=0A=
> --- a/drivers/crypto/caam/caamrng.c=0A=
> +++ b/drivers/crypto/caam/caamrng.c=0A=
> @@ -202,7 +202,8 @@ static inline int rng_create_sh_desc(struct caam_rng_=
ctx *ctx)=0A=
>  	init_sh_desc(desc, HDR_SHARE_SERIAL);=0A=
>  =0A=
>  	/* Generate random bytes */=0A=
> -	append_operation(desc, OP_ALG_ALGSEL_RNG | OP_TYPE_CLASS1_ALG);=0A=
> +	append_operation(desc, OP_ALG_ALGSEL_RNG | OP_TYPE_CLASS1_ALG |=0A=
> +			 OP_ALG_PR_ON);=0A=
>  =0A=
>  	/* Store bytes */=0A=
>  	append_seq_fifo_store(desc, RN_BUF_SIZE, FIFOST_TYPE_RNGSTORE);=0A=
> diff --git a/drivers/crypto/caam/ctrl.c b/drivers/crypto/caam/ctrl.c=0A=
> index df4db10e9fca..a1c879820286 100644=0A=
> --- a/drivers/crypto/caam/ctrl.c=0A=
> +++ b/drivers/crypto/caam/ctrl.c=0A=
> @@ -36,7 +36,8 @@ static void build_instantiation_desc(u32 *desc, int han=
dle, int do_sk)=0A=
>  	init_job_desc(desc, 0);=0A=
>  =0A=
>  	op_flags =3D OP_TYPE_CLASS1_ALG | OP_ALG_ALGSEL_RNG |=0A=
> -			(handle << OP_ALG_AAI_SHIFT) | OP_ALG_AS_INIT;=0A=
> +			(handle << OP_ALG_AAI_SHIFT) | OP_ALG_AS_INIT |=0A=
> +			OP_ALG_PR_ON;=0A=
>  =0A=
>  	/* INIT RNG in non-test mode */=0A=
>  	append_operation(desc, op_flags);=0A=
> @@ -275,11 +276,12 @@ static int instantiate_rng(struct device *ctrldev, =
int state_handle_mask,=0A=
>  		return -ENOMEM;=0A=
>  =0A=
>  	for (sh_idx =3D 0; sh_idx < RNG4_MAX_HANDLES; sh_idx++) {=0A=
> +		const u32 rdsta_mask =3D (RDSTA_PR0 | RDSTA_IF0) << sh_idx;=0A=
>  		/*=0A=
>  		 * If the corresponding bit is set, this state handle=0A=
>  		 * was initialized by somebody else, so it's left alone.=0A=
>  		 */=0A=
> -		if ((1 << sh_idx) & state_handle_mask)=0A=
> +		if (rdsta_mask & state_handle_mask)=0A=
>  			continue;=0A=
>  =0A=
If a state handle was previously instantiated (e.g. by U-boot),=0A=
but without prediction resistance support, it won't be re-instantiated=0A=
("continue" / skip above).=0A=
=0A=
The result is using a state handle without PR support.=0A=
Due to this, when extracting / generating randomness (in caamrng.c) with=0A=
the PR bit set, job descriptor will generate a prediction resistance error.=
=0A=
=0A=
IMO the proper thing to do in case a state handle was instantiated=0A=
without PR support is to re-instantiate it.=0A=
=0A=
There's an assumption here though: kernel handles RNG initialization only=
=0A=
in some cases, when it's effectively "controlling" it.=0A=
In cases when it's not, like when Management Complex (MC) f/w is present=0A=
(or OP-TEE OS, SECO etc.), kernel skips RNG init and only uses the job ring=
=0A=
interface for random generation.=0A=
=3D=3D> MC, OP-TEE, SECO etc. have to be updated to initialize=0A=
RNG state handles with PR support=0A=
=0A=
Horia=0A=