On 06/11/2015 06:34 PM, Kevin O'Connor wrote:
On Wed, Jun 10, 2015 at 10:58:40AM -0400, Stefan Berger wrote:
On 06/10/2015 10:38 AM, Kevin O'Connor wrote:
Thanks. It does look much better to me. What's the difference
between enabled and activated? Can you describe it or point me to a
link?
So I'll ditch the physical presence part for now , ditch that bool patch and
post the menu patch on top of the cleanups.
Here the link to the documentation about the TPM 1.2 states:
http://www.trustedcomputinggroup.org/resources/tpm_main_specification
Access document Part 1 - Design Principles. Section 9.4 and subsections
explain the different states of the TPM 1.2.
From the spec 9.4.1:
"A disabled TPM is not able to execute commands that use the
resources of a TPM. While some commands are available (SHA-1 for
example) the TPM is not able to load keys and perform TPM_Seal and
other such operations. These restrictions are the same as for an
inactive TPM. The difference between inactive and disabled is that a
disabled TPM is unable to execute the TPM_TakeOwnership command. A
disabled TPM that has a TPM Owner is not able to execute normal TPM
commands."
From the spec 9.4.2:
"A deactivated TPM is not able to execute commands that use TPM
resources. A major difference between deactivated and disabled is
that a deactivated TPM CAN execute the TPM_TakeOwnership
command. [...]"
Thanks. Unfortunately I'm still confused.
The above seems to say that the only difference between disabled and
deactivated is that one can't take ownership of a disabled TPM. But,
if that's the case, when a tpm is active, why does the menu provide
for both "Deactivate the TPM" and "Prevent installation of an owner"?
(And, why would anyone want to take "ownership" of a TPM that is
disabled/deactivated anyway?)
From that link to the TPM 1.2 specs you see in section 9.4 that there
are actually 3 independent state bits of the TPM:
- active/deactivated
- enabled/disabled
- taking ownership is possible / is not possible
These 3 bits can only be modified while one interacts with the firmware
( physical presence must be asserted ). I am giving control in the menu
over these 3 bits because the firmware is the right and only place to do
this. I admit that these fine grained controls are confusing, though
that's the controls TPM 1.2 allows per its spec.
Stefan
-Kevin
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