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

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Date:   Wed, 22 Jan 2020 13:37:11 +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 1/21/2020 6:38 PM, Horia Geanta wrote:
> 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)
> instantiate_rng() is called with
> 	state_handle_mask = rd_reg32(&ctrl->r4tst[0].rdsta) & RDSTA_IFMASK;
> so if (rdsta_pr & state_handle_mask) will always be false,
> leading to unneeded state handle re-initialization.
> 
Sorry, I missed this change:
-#define RDSTA_IFMASK (RDSTA_IF1 | RDSTA_IF0)
+#define RDSTA_IFMASK (RDSTA_PR1 | RDSTA_PR0 | RDSTA_IF1 | RDSTA_IF0)

which means code is correct (though I must admit not so intuitive).

Horia