Hi Mimi,
On 7/20/21 7:33 PM, Mimi Zohar wrote:
Hi Tushar, Mike,
On Mon, 2021-07-12 at 17:49 -0700, Tushar Sugandhi wrote:
+Then IMA ASCII measurement log has the following format:
+PCR TEMPLATE_DIGEST TEMPLATE ALG:EVENT_DIGEST EVENT_NAME EVENT_DATA
+
+PCR := Platform Configuration Register, in which the values are registered.
+ This is applicable if TPM chip is in use.
+TEMPLATE_DIGEST := Template digest of the IMA record.
^TEMPLATE_DATA_DIGEST
Will do.
+TEMPLATE := Template that registered the integrity value (e.g. ima-buf).
^TEMPLATE_NAME
Will do.
The template data format consists of:
+ALG:EVENT_DIGEST = Algorithm to compute event digest, followed by digest of event data
+EVENT_NAME := Description of the event (e.g. 'table_load').
+EVENT_DATA := The event data to be measured.
Thanks. I will add this to the dm-ima documentation.
Missing from the document is a way of validating the template data.
For example, in the original case of file measurements, the template
data contains the file hash, which can be recalculated or verified
against an allow list.
Other than re-calculating the template data digest based on the
template data, and verifying it against the template data digest in the
measurement list, would an attestation server be able to verify the
template data itself?
Yes.
In the context of device-mapper, EVENT_DATA for 'table_load' would
contain the key-value pairs for various targets in the table
(crypt, verity, integrity etc.) which the attestation servers
should be able to verify against the allowed/expected
key-value pairs specified in the attestation policy.
To avoid bloating the IMA log with same data from table_load again,
we only measure hash of the loaded table in the EVENT_DATA -
when there is a state change for DM device.
e.g. when EVENT_NAME is 'device_resume', 'table_clear',
'device_remove' etc.
Since the table clear-text is already present in the EVENT_DATA
buffer for 'table_load', and is available to attestation servers,
verifying the corresponding hash values in the
EVENT_DATA in the subsequent DM events should be possible for
the attestation servers.
Please let us know if you need further info.
Thanks,
Tushar
thanks,
Mimi
