Re: [Linux-ima-user] [PATCH] ima: platform-independent hash value

[Roberto S. <rob...@po...>]

On 05/15/2014 08:55 AM, Dmitry Kasatkin wrote:
> On 15 May 2014 00:32, Mimi Zohar <zo...@li...> wrote:
>> On Wed, 2014-05-07 at 18:13 +0200, Andreas Steffen wrote:
>>> For remote attestion it is important for the ima measurement values
>>> to be platform-independent. Therefore integer fields to be hashed
>>> must be converted to network order first.
>>>
>>> Signed-off-by: Andreas Steffen <and...@st...>
>>> ---
>>>   security/integrity/ima/ima_crypto.c | 5 +++--
>>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/security/integrity/ima/ima_crypto.c b/security/integrity/ima/ima_crypto.c
>>> index 1bde8e6..8725bff 100644
>>> --- a/security/integrity/ima/ima_crypto.c
>>> +++ b/security/integrity/ima/ima_crypto.c
>>> @@ -170,11 +170,12 @@ static int ima_calc_field_array_hash_tfm(struct ima_field_data *field_data,
>>>                u8 buffer[IMA_EVENT_NAME_LEN_MAX + 1] = { 0 };
>>>                u8 *data_to_hash = field_data[i].data;
>>>                u32 datalen = field_data[i].len;
>>> +             u32 datalen_to_hash = htonl(datalen);
>>>
>>>                if (strcmp(td->name, IMA_TEMPLATE_IMA_NAME) != 0) {
>>>                        rc = crypto_shash_update(&desc.shash,
>>> -                                             (const u8 *) &field_data[i].len,
>>> -                                             sizeof(field_data[i].len));
>>> +                                             (const u8 *) &datalen_to_hash,
>>> +                                             sizeof(datalen_to_hash));
>>>                        if (rc)
>>>                                break;
>>>                } else if (strcmp(td->fields[i]->field_id, "n") == 0) {
>>
>> After thinking about this some more, and discussing it with Roberto and
>> Dave, this change is probably unnecessary.  Assuming the measurement
>> list is sent in host native format, a hash of the template data will
>> match the value contained in the measurement list.  Only if the template
>> data is converted to network byte order, prior to sending it, would
>> there be a problem.
>>
>> The PCR value provides a good heuristic for determining the data
>> endianness.
>>
>
> So you suggestion is try to change endianness if PCR reconstruction fails?
>
>
> BTW.
>
> Remote attestation agent is sending measurement list to the remote
> attestation server.
> Can agent also send "endianness" of the attested client?
>

Hi Dmitry

I think yes. I'm not aware of a standardized way to do it,
but this information could be included in integrity reports
(within the XML whose format is defined by the TCG).

Roberto


> - Dmitry
>
>> Mimi
>>
>
>
>