linux-kernel - Re: [RESEND PATCH 6/6] crypto: caam: detect RNG init when TrustZone is active

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Message-ID: <1516886454.3733.23.camel@aisec.fraunhofer.de>
Date:   Thu, 25 Jan 2018 13:20:55 +0000
From:   "Auer, Lukas" <lukas.auer@...ec.fraunhofer.de>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "aymen.sghaier@....com" <aymen.sghaier@....com>,
        "horia.geanta@....com" <horia.geanta@....com>,
        "pure.logic@...us-software.ie" <pure.logic@...us-software.ie>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>
CC:     "peng.fan@....com" <peng.fan@....com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "ryan.harkin@...aro.org" <ryan.harkin@...aro.org>,
        "fabio.estevam@....com" <fabio.estevam@....com>,
        "rui.silva@...aro.org" <rui.silva@...aro.org>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>
Subject: Re: [RESEND PATCH 6/6] crypto: caam: detect RNG init when TrustZone
 is active

On Wed, 2018-01-24 at 14:50 +0000, Bryan O'Donoghue wrote:
> When TrustZone is enabled on sec4 compatible silicon the first page
> of the
> CAAM is reserved for TrustZone only, this means that access to the
> deco
> registers is restricted and will return zero when read.
> 
> The solution to this problem is to initialize the RNG prior to
> TrustZone
> being enabled or to initialize the RNG from a TrustZone context and
> simultaneously to ensure that the job-ring registers have been
> assigned to
> the correct non-TrustZone context.
> 
> Assigning of the job-ring registers is a task for u-boot or
> OPTEE/TrustZone
> as is the initialization of the RNG. This patch adds logic to detect
> RNG
> initialization if and only if TrustZone has been detected as active
> on the
> CAAM block.
> 
> If TrustZone is initialized and the RNG looks to be setup - we mark
> the RNG
> as good to go and continue to load, else we mark the RNG as bad and
> bail
> out.
> 
> More detail on the original problem and the split fix between u-boot
> and
> Linux is available in these two threads
> 
> Link: https://github.com/OP-TEE/optee_os/issues/1408
> Link: https://tinyurl.com/yam5gv9a
> Link: https://patchwork.ozlabs.org/cover/865042
> 
> Signed-off-by: Bryan O'Donoghue <pure.logic@...us-software.ie>
> Cc: "Horia Geantă" <horia.geanta@....com>
> Cc: Aymen Sghaier <aymen.sghaier@....com>
> Cc: Fabio Estevam <fabio.estevam@....com>
> Cc: Peng Fan <peng.fan@....com>
> Cc: Herbert Xu <herbert@...dor.apana.org.au>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Lukas Auer <lukas.auer@...ec.fraunhofer.de>
> ---
>  drivers/crypto/caam/ctrl.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/crypto/caam/ctrl.c b/drivers/crypto/caam/ctrl.c
> index 7fd3bfc..66a7c7e 100644
> --- a/drivers/crypto/caam/ctrl.c
> +++ b/drivers/crypto/caam/ctrl.c
> @@ -711,6 +711,24 @@ static int caam_probe(struct platform_device
> *pdev)
>  			int inst_handles =
>  				rd_reg32(&ctrl->r4tst[0].rdsta) &
>  								RDST
> A_IFMASK;
> +
> +			/*
> +			 * If TrustZone is active then u-boot or the
> TrustZone
> +			 * firmware must have initialized the RNG
> for us else we
> +			 * cannot do so from Linux.
> +			 *
> +			 * We've previously detected TrustZone so
> now let's
> +			 * detect if the RNG has been initialized.
> +			 */
> +			if (ctrlpriv->trust_zone) {
> +				ret = -ENODEV;
> +				if (ctrlpriv->rng4_sh_init ||
> inst_handles)
> +					ret = 0;
> +				dev_info(dev, "TrustZone active RNG
> looks %s\n",
> +					 ret ? "uninitialized" :
> "initialized");
> +				break;
> +			}
> +
>  			/*
>  			 * If either SH were instantiated by
> somebody else
>  			 * (e.g. u-boot) then it is assumed that the
> entropy

This (in addition to patch 5) should not be required if all RNG state
handles are already instantiated. The instantiate_rng() function checks
each state handle if it is already instantiated before trying to do so
itself. DEC0 would therefore never be used and the probe call should
succeed in non-secure mode.

I have submitted a patch [1] to u-boot that instantiates all RNG state
handles.

Thanks,
Lukas

[1] https://www.mail-archive.com/u-boot@lists.denx.de/msg276184.html