Re: [PATCH v6 5/7] tpm: retrieve digest size of unknown algorithms with PCR read

From: Roberto Sassu <roberto.sassu@huawei.com>
To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: <zohar@linux.ibm.com>, <david.safford@ge.com>,
	<monty.wiseman@ge.com>, <linux-integrity@vger.kernel.org>,
	<linux-security-module@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>, <silviu.vlasceanu@huawei.com>
Subject: Re: [PATCH v6 5/7] tpm: retrieve digest size of unknown algorithms with PCR read
Date: Thu, 6 Dec 2018 19:00:13 +0100	[thread overview]
Message-ID: <ac404fdd-b673-eb49-d6e7-4fc6de561ce1@huawei.com> (raw)
In-Reply-To: <20181204235354.GD1233@linux.intel.com>

On 12/5/2018 12:53 AM, Jarkko Sakkinen wrote:
> On Tue, Dec 04, 2018 at 09:21:36AM +0100, Roberto Sassu wrote:
>> +	for (i = 0; i < ARRAY_SIZE(tpm2_hash_map); i++) {
>> +		enum hash_algo crypto_algo = tpm2_hash_map[i].crypto_id;
>> +
>> +		if (bank->alg_id != tpm2_hash_map[i].tpm_id)
>> +			continue;
>> +
>> +		bank->digest_size = hash_digest_size[crypto_algo];
>> +		bank->crypto_id = crypto_algo;
>> +		return 0;
>> +	}
>> +
>> +	return tpm2_pcr_read(chip, 0, &digest, &bank->digest_size);
>> +}
> 
> This is a part that I don't get. Coud you just always call
> tpm2_pcr_read() instead of this complexity

First, we avoid operations that may increase the boot time. Second, the
loop is necessary to obtain the crypto subsystem identifier from a TPM
algorithm identifier.

Roberto

> /Jarkko
> 

-- 
HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Bo PENG, Jian LI, Yanli SHI