linux-kernel - Re: [PATCH] s390/zcrypt: enable s390 hwrng to seed kernel entropy

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Date:	Mon, 11 Aug 2014 17:11:52 +0200
From:	Ingo Tuchscherer <ingo.tuchscherer@...ux.vnet.ibm.com>
To:	Torsten Duwe <duwe@....de>,
	Ingo Tuchscherer <ingo.tuchscherer@...ibm.com>
CC:	linux-kernel@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Gerald Schaefer <gerald.schaefer@...ibm.com>,
	Heiko Carstens <heicars2@...ux.vnet.ibm.com>,
	Hendrik Brueckner <brueckner@...ibm.com>,
	Matt Mackall <mpm@...enic.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Harald Freudenberger <freude@...ibm.com>
Subject: Re: [PATCH] s390/zcrypt: enable s390 hwrng to seed kernel entropy

On 08/11/2014 03:56 PM, Torsten Duwe wrote:
> On Wed, Jul 30, 2014 at 02:17:36PM +0200, Ingo Tuchscherer wrote:
>> Set the 'quality' property in the zcrypt rng device structure to enable the
>> zcrypt hwrng device to take part in the kernel entropy seeding process.
>> A module parameter named hwrng_seed will be introduced to disable the
>> participation. By default this parameter is set to 1 (enabled).
> I only had a one-liner that simply enabled it. I guess the extra switch
> is for certification scenarios?
I introduced this switch for several reasons. I would like to have the 
possibility to prevent the card from being interrupted with rng queries 
(in case of heavy workload) or card verification/certification or other 
measurement processes.
Last but not least we are able to deactivate this feature in case of any 
failures/attacks.

> Anyway,
>
> Acked-by: Torsten Duwe <duwe@...e.de>
>> Signed-off-by: Ingo Tuchscherer <ingo.tuchscherer@...ibm.com>
>> ---
>>   drivers/s390/crypto/ap_bus.c     | 5 +++++
>>   drivers/s390/crypto/ap_bus.h     | 1 +
>>   drivers/s390/crypto/zcrypt_api.c | 3 +++
>>   3 files changed, 9 insertions(+)
>>
>> diff --git a/drivers/s390/crypto/ap_bus.c b/drivers/s390/crypto/ap_bus.c
>> index 4038437..19fac5f 100644
>> --- a/drivers/s390/crypto/ap_bus.c
>> +++ b/drivers/s390/crypto/ap_bus.c
>> @@ -85,6 +85,11 @@ static int ap_thread_flag = 0;
>>   module_param_named(poll_thread, ap_thread_flag, int, S_IRUSR|S_IRGRP);
>>   MODULE_PARM_DESC(poll_thread, "Turn on/off poll thread, default is 0 (off).");
>>   
>> +int ap_hwrng_seed = 1;
>> +EXPORT_SYMBOL(ap_hwrng_seed);
>> +module_param_named(hwrng_seed, ap_hwrng_seed, int, S_IRUSR|S_IRGRP);
>> +MODULE_PARM_DESC(hwrng_seed, "Turn on/off hwrng auto seed, default is 1 (on).");
>> +
>>   static struct device *ap_root_device = NULL;
>>   static struct ap_config_info *ap_configuration;
>>   static DEFINE_SPINLOCK(ap_device_list_lock);
>> diff --git a/drivers/s390/crypto/ap_bus.h b/drivers/s390/crypto/ap_bus.h
>> index 6405ae2..b0be09a 100644
>> --- a/drivers/s390/crypto/ap_bus.h
>> +++ b/drivers/s390/crypto/ap_bus.h
>> @@ -38,6 +38,7 @@
>>   #define AP_POLL_TIME 1		/* Time in ticks between receive polls. */
>>   
>>   extern int ap_domain_index;
>> +extern int ap_hwrng_seed;
>>   
>>   /**
>>    * The ap_qid_t identifier of an ap queue. It contains a
>> diff --git a/drivers/s390/crypto/zcrypt_api.c b/drivers/s390/crypto/zcrypt_api.c
>> index 0e18c5d..ed91665 100644
>> --- a/drivers/s390/crypto/zcrypt_api.c
>> +++ b/drivers/s390/crypto/zcrypt_api.c
>> @@ -1374,6 +1374,7 @@ static int zcrypt_rng_data_read(struct hwrng *rng, u32 *data)
>>   static struct hwrng zcrypt_rng_dev = {
>>   	.name		= "zcrypt",
>>   	.data_read	= zcrypt_rng_data_read,
>> +	.quality	= 990,
>>   };
>>   
>>   static int zcrypt_rng_device_add(void)
>> @@ -1388,6 +1389,8 @@ static int zcrypt_rng_device_add(void)
>>   			goto out;
>>   		}
>>   		zcrypt_rng_buffer_index = 0;
>> +		if (!ap_hwrng_seed)
>> +			zcrypt_rng_dev.quality = 0;
>>   		rc = hwrng_register(&zcrypt_rng_dev);
>>   		if (rc)
>>   			goto out_free;
>> -- 
>> 1.8.5.5
>>
>> --
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