From: Roberto Sassu <roberto.sassu@huawei.com>
To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: tpmdd-devel@lists.sourceforge.net,
linux-ima-devel@lists.sourceforge.net,
linux-security-module@vger.kernel.org, keyrings@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/5] tpm: introduce tpm_pcr_algo_to_crypto() and tpm_pcr_algo_from_crypto()
Date: Tue, 30 May 2017 12:24:21 +0200 [thread overview]
Message-ID: <c484dc54-7d19-9d60-bd17-4ac47f1bc218@huawei.com> (raw)
In-Reply-To: <20170524202523.grpg7ocrwwuzxsbg@intel.com>
On 5/24/2017 10:25 PM, Jarkko Sakkinen wrote:
> On Wed, May 24, 2017 at 10:33:54AM -0700, Jarkko Sakkinen wrote:
>> On Mon, May 22, 2017 at 09:21:28AM +0200, Roberto Sassu wrote:
>>> On 5/20/2017 3:22 PM, Jarkko Sakkinen wrote:
>>>> On Mon, May 15, 2017 at 04:22:22PM +0200, Roberto Sassu wrote:
>>>>> On 5/15/2017 1:16 PM, Jarkko Sakkinen wrote:
>>>>>> On Fri, May 05, 2017 at 04:21:49PM +0200, Roberto Sassu wrote:
>>>>>>> tpm_pcr_algorithms() returns to its callers the IDs of the hash algorithms
>>>>>>> supported by the TPM. This patch introduces tpm_pcr_algo_to_crypto(),
>>>>>>> so that the callers can use the crypto subsystem to calculate the digest
>>>>>>> to be passed to tpm_pcr_extend().
>>>>>>>
>>>>>>> tpm_pcr_algo_from_crypto(), implemented for completeness, is instead used
>>>>>>
>>>>>> What do you mean by completeness? Please, never add unused stuff.
>>>>>>
>>>>>>> by tpm2_seal_trusted() to perform the opposite conversion.
>>>>>>>
>>>>>>> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
>>>>>>> ---
>>>>>>> v2
>>>>>>>
>>>>>>> - fixed return values of tpm2_pcr_algo_to_crypto() and
>>>>>>> tpm2_pcr_algo_from_crypto() if TPM support is disabled in the kernel
>>>>>>
>>>>>> Change Log only to the cover letter.
>>>>>>
>>>>>>> drivers/char/tpm/tpm-interface.c | 51 ++++++++++++++++++++++++++++++++++++++++
>>>>>>> drivers/char/tpm/tpm2-cmd.c | 42 +++++++++------------------------
>>>>>>> include/linux/tpm.h | 13 ++++++++++
>>>>>>> 3 files changed, 75 insertions(+), 31 deletions(-)
>>>>>>
>>>>>> This commit is just deadly wrong in so many ways.
>>>>>>
>>>>>> I would suggest to make extend always just take crypto ID in so you
>>>>>> don't have to add these bizarre conversion functions.
>>>>>
>>>>> The reason of this choice (as I explained in the cover letter)
>>>>> is that TPM users might want to produce an event log with
>>>>> the TCG format (which includes the TPM algorithm ID). Also,
>>>>> TPM IDs should be preferred because, with them, TPM users
>>>>> can calculate a digest directly with the TPM.
>>>>>
>>>>> Taking crypto IDs means relying on the fact that there
>>>>> is always a mapping between TPM IDs and crypto IDs.
>>>>> Otherwise, tpm_pcr_algorithms() cannot return the algorithms
>>>>> to its callers and PCRs cannot be extended. If TPM IDs are used,
>>>>> TPM users have two alternatives: calculate the digest with
>>>>> the TPM, or pass a SHA1 digest to tpm_pcr_extend(), so that
>>>>> it can be padded to extend remanining PCR banks.
>>>>>
>>>>> However, this second option will work only when the TPM driver
>>>>> determines the size of an algorithm without relying on the crypto
>>>>> subsystem. At the moment, if a TPM ID is not mapped to a crypto ID,
>>>>> tpm2_pcr_extend() ignores the digest.
>>>>>
>>>>> Roberto
>>>>
>>>> What if tpm_pcr_algorithms would convert TPM IDs to crypto IDs?
>>>>
>>>> Externally other subsystems would have to then deal with only crypto
>>>> IDs.
>>>
>>> Then, other subsystems cannot:
>>>
>>> - use the TPM to calculate a digest
>>> - create an event log with the TCG format
>>>
>>> Roberto
>>
>> Can you open this up a bit? What is the use case that you canno
>> implement?
>>
>> /Jarkko
>
> The most important question is: are this used *right now*. If not, it is
> a definitive NAK. We don't want any future-proof code to the kernel.
> Always do the lowest common denominator in terms of generality and we
> will refactor from there when need arises.
This is still being discussed.
If we use crypto IDs, as you suggested, what it should be passed
to tpm_pcr_extend()? Or, probably to a new function (Mimi said that
changing the parameters of an existing function is not bisect-safe).
Roberto
--
HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Bo PENG, Qiuen PENG, Shengli WANG
next prev parent reply other threads:[~2017-05-30 10:24 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-05 14:21 [PATCH v2 0/5] Updated API for TPM 2.0 PCR extend Roberto Sassu
2017-05-05 14:21 ` [PATCH v2 1/5] tpm: introduce tpm_pcr_algorithms() Roberto Sassu
2017-05-15 10:36 ` Jarkko Sakkinen
[not found] ` <20170515103623.sumyo2vyldezual2-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-05-15 13:18 ` Roberto Sassu
[not found] ` <d2974dd2-e30d-e8f0-a60a-2147f3290670-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
2017-05-17 8:42 ` Roberto Sassu
2017-05-20 13:18 ` Jarkko Sakkinen
[not found] ` <20170520131846.e3niqiknlrttbdf4-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-05-22 9:07 ` Roberto Sassu
2017-05-24 17:35 ` Jarkko Sakkinen
[not found] ` <20170524173521.yiiohct7brkcozyk-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-05-30 8:44 ` Roberto Sassu
[not found] ` <1cf4fbb1-5683-ceb4-2d5b-8ade25a91e83-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
2017-05-31 11:39 ` Jarkko Sakkinen
2017-05-20 13:00 ` Jarkko Sakkinen
2017-05-05 14:21 ` [PATCH v2 2/5] tpm: introduce tpm_pcr_algo_to_crypto() and tpm_pcr_algo_from_crypto() Roberto Sassu
[not found] ` <20170505142152.29795-3-roberto.sassu-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
2017-05-15 11:16 ` Jarkko Sakkinen
[not found] ` <20170515111629.urjvbhqzohv4vakc-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-05-15 14:22 ` Roberto Sassu
2017-05-20 13:22 ` Jarkko Sakkinen
[not found] ` <20170520132217.t7n7l2pjn7i63hbm-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2017-05-22 7:21 ` Roberto Sassu
2017-05-24 17:33 ` Jarkko Sakkinen
2017-05-24 20:25 ` Jarkko Sakkinen
2017-05-30 10:24 ` Roberto Sassu [this message]
2017-05-31 11:40 ` Jarkko Sakkinen
2017-05-05 14:21 ` [PATCH v2 3/5] tpm: pass multiple digests to tpm_pcr_extend() Roberto Sassu
[not found] ` <20170505142152.29795-4-roberto.sassu-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
2017-05-30 3:29 ` [Linux-ima-devel] " Mimi Zohar
2017-05-30 7:28 ` Roberto Sassu
2017-05-30 11:25 ` Mimi Zohar
[not found] ` <1496143547.3841.517.camel-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
2017-05-30 13:25 ` Roberto Sassu
2017-05-05 14:21 ` [PATCH v2 4/5] keys, trusted: modify arguments of tpm_pcr_extend() Roberto Sassu
2017-05-30 3:35 ` [Linux-ima-devel] " Mimi Zohar
[not found] ` <1496115337.3841.485.camel-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
2017-05-30 7:36 ` Roberto Sassu
2017-05-30 12:06 ` Mimi Zohar
[not found] ` <1496145961.3841.537.camel-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
2017-05-30 13:41 ` Roberto Sassu
2017-05-05 14:21 ` [PATCH v2 5/5] ima: " Roberto Sassu
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