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From: Roberto Sassu <roberto.sassu-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
To: Jarkko Sakkinen
	<jarkko.sakkinen-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
Cc: linux-ima-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org,
	linux-security-module-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	tpmdd-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org,
	keyrings-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH v2 1/5] tpm: introduce tpm_pcr_algorithms()
Date: Mon, 22 May 2017 11:07:54 +0200	[thread overview]
Message-ID: <cc7efaa2-4d5b-2142-3b23-06864589c212@huawei.com> (raw)
In-Reply-To: <20170520131846.e3niqiknlrttbdf4-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>

On 5/20/2017 3:18 PM, Jarkko Sakkinen wrote:
> On Wed, May 17, 2017 at 10:42:35AM +0200, Roberto Sassu wrote:
>> On 5/15/2017 3:18 PM, Roberto Sassu wrote:
>>>
>>>
>>> On 5/15/2017 12:36 PM, Jarkko Sakkinen wrote:
>>>> On Fri, May 05, 2017 at 04:21:48PM +0200, Roberto Sassu wrote:
>>>>> This function allows TPM users to know which algorithms the TPM
>>>>> supports.
>>>>> It stores the algorithms in a static array of 'enum tpm2_algorithms',
>>>>> allocated by the caller. If the array is not large enough, the function
>>>>> returns an error. Otherwise, it returns the number of algorithms written
>>>>> to the array. If the TPM version is 1.2, the function writes
>>>>> TPM2_ALG_SHA1
>>>>> to first element of the array.
>>>>>
>>>>> Writing the algorithm also for TPM 1.2 has the advantage that callers
>>>>> can use the API, tpm_pcr_algorithms() and tpm_pcr_extend(), regardless
>>>>> of the TPM version.
>>>>>
>>>>> A minor change added to this patch was to make available the size of
>>>>> the active_banks array, member of the tpm_chip structure, outside
>>>>> the TPM driver. The array size (TPM_ACTIVE_BANKS_MAX) has been exported
>>>>> to include/linux/tpm.h.
>>>>>
>>>>> With this information, callers of tpm_pcr_algorithms() can provide
>>>>> a static array with enough room for all the algorithms, instead
>>>>> of receiving the pointer of a dynamic array that they have to free
>>>>> later.
>>>>>
>>>>> Signed-off-by: Roberto Sassu <roberto.sassu-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
>>>>> ---
>>>>> v2
>>>>>
>>>>> - tpm_pcr_algorithms() returns supported algorithms also for TPM 1.2
>>>>>
>>>>>  drivers/char/tpm/tpm-interface.c | 46
>>>>> ++++++++++++++++++++++++++++++++++++++++
>>>>>  drivers/char/tpm/tpm.h           | 13 +-----------
>>>>>  include/linux/tpm.h              | 19 +++++++++++++++++
>>>>>  3 files changed, 66 insertions(+), 12 deletions(-)
>>>>>
>>>>> diff --git a/drivers/char/tpm/tpm-interface.c
>>>>> b/drivers/char/tpm/tpm-interface.c
>>>>> index 4ed08ab..b90de3d 100644
>>>>> --- a/drivers/char/tpm/tpm-interface.c
>>>>> +++ b/drivers/char/tpm/tpm-interface.c
>>>>> @@ -911,6 +911,52 @@ int tpm_pcr_extend(u32 chip_num, int pcr_idx,
>>>>> const u8 *hash)
>>>>>  EXPORT_SYMBOL_GPL(tpm_pcr_extend);
>>>>>
>>>>>  /**
>>>>> + * tpm_pcr_algorithms - get TPM IDs of active PCR banks algorithms
>>>>
>>>> The grammar is incorrect here I believe. Should rather be
>>>>
>>>>   "algorithms of the active PCR banks"
>>>>
>>>> And there is no such thing as "TPM ID".
>>>>
>>>>> + * @chip_num:    tpm idx # or ANY
>>>>> + * @count:    # of items in algorithms
>>>>> + * @algorithms:    array of TPM IDs
>>>>> + *
>>>>> + * Returns < 0 on error, and the number of active PCR banks on success.
>>>>> + *
>>>>> + * TPM 1.2 has always one SHA1 bank.
>>>>> + */
>>>>> +int tpm_pcr_algorithms(u32 chip_num, int count,
>>>>> +               enum tpm2_algorithms *algorithms)
>>>>                        unsigned int
>>>>
>>>> In addition the function name is not too greatg,
>>>>
>>>> Your syntax for return value is not correct. In addition after
>>>> describing the return value there should not be anything. You should
>>>> study
>>>>
>>>> https://www.kernel.org/doc/Documentation/kernel-doc-nano-HOWTO.txt
>>>>
>>>> Better name for the function would be tpm_get_pcr_algorithms().
>>>>
>>>>> +{
>>>>> +    struct tpm_chip *chip;
>>>>> +    int i;
>>>>> +
>>>>> +    if (count <= 0 || algorithms == NULL)
>>>>> +        return -EINVAL;
>>>>
>>>> Is there a legal case where caller would pass these values? Now it
>>>> looks like that there is.
>>>>
>>>> 'count' should unsigned int and zero should be a legal value for
>>>> count.
>>>
>>> I wanted to avoid that a negative value returned by tpm_pcr_algorithms()
>>> is passed to tpm_pcr_extend() as unsigned int.
>>>
>>>
>>>> That said I think the whole design is wrong as you could calculate
>>>> array for algs only one time and pass a const reference to it on
>>>> request.
>>>
>>> Ok. If I understood it correctly, you are saying to pass a const
>>> reference of chip->active_banks. Then, I should also:
>>
>> This is not a viable option. chip could be freed and the reference
>> becomes invalid, without increasing the reference count.
>>
>> Did you think about something different?
>>
>> Thanks
>>
>> Roberto
>
> Two alternatives come in mind.
>
> 1. add tpm_put to linclude/linux/tpm.h
> 2. take put_ops away from the implementation
> 3. add documentation that tpm_put needs to be called
>
> or acceptable alternative would memcpy in the implementation
>
> In any case, you should probably drop completely 'count' and have
> function for getting the number of active banks.

Having a variable number, makes things more complicated.
In the IMA patch set for multiple template digests,
the array of algorithms is stored inside a structure
called digest descriptor. The array size must be fixed,
to avoid VLAIS (which is not supported by clang).

Since the size of tpm_chip->active_banks is a small number,
we can drop count, and assume that the size of the array
passed to tpm_pcr_algorithms() always matches the size
of the active_banks array.

Roberto

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  parent reply	other threads:[~2017-05-22  9:07 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 [this message]
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
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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