linux-kernel - Re: [PATCH v6 6/7] crypto: caam - enable prediction resistance in HRWNG

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Message-ID: <VI1PR0402MB3485F1AF6DC4B74FF373B16998320@VI1PR0402MB3485.eurprd04.prod.outlook.com>
Date:   Mon, 20 Jan 2020 16:38:46 +0000
From:   Horia Geanta <horia.geanta@....com>
To:     Andrey Smirnov <andrew.smirnov@...il.com>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>
CC:     Chris Healy <cphealy@...il.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Iuliana Prodan <iuliana.prodan@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH v6 6/7] crypto: caam - enable prediction resistance in
 HRWNG

On 1/8/2020 5:42 PM, Andrey Smirnov wrote:
> @@ -275,12 +276,25 @@ static int instantiate_rng(struct device *ctrldev, int state_handle_mask,
>  		return -ENOMEM;
>  
>  	for (sh_idx = 0; sh_idx < RNG4_MAX_HANDLES; sh_idx++) {
> +		const u32 rdsta_if = RDSTA_IF0 << sh_idx;
> +		const u32 rdsta_pr = RDSTA_PR0 << sh_idx;
> +		const u32 rdsta_mask = rdsta_if | rdsta_pr;
>  		/*
>  		 * If the corresponding bit is set, this state handle
>  		 * was initialized by somebody else, so it's left alone.
>  		 */
> -		if ((1 << sh_idx) & state_handle_mask)
> -			continue;
> +		if (rdsta_if & state_handle_mask) {
> +			if (rdsta_pr & state_handle_mask)
> +				continue;
> +
> +			dev_info(ctrldev,
> +				 "RNG4 SH%d was previously instantiated without prediction resistance. Tearing it down\n",
> +				 sh_idx);
> +
> +			ret = deinstantiate_rng(ctrldev, rdsta_if);
> +			if (ret)
> +				break;
In case state handle 0 is deinstantiated, its reinstantiation with PR support
will have the side effect of re-generating JDKEK, TDKEK, TDSK.
This needs to be avoided, since other SW components (like OP-TEE f/w)
could have black keys in use. Overwriting the KEK registers would no longer
allow CAAM to decrypt them.

Horia