Re: [tboot-devel] Questions about Launch Control Policies

[Marco V. <mva...@go...>]

Thanks for your answer, Ning.

I have been using tpm2.0-tools and tpm2.0-TSS to work with the TPM. They
have been very useful so far :).

I have a couple more questions regarding the Intel TXT Guide:

The Intel TXT Guide (Appendix J "TPM NV") says that the NVRAM PO Index
should have the following attributes:
    - TPMA_NV_OWNERWRITE
    - TPMA_NV_POLICYWRITE
    - TPMA_NV_AUTHREAD
    - TPMA_NV_NO_DA

That sets of attributes translate to 0x204000A, but that results in a
0xc0081c41 TXT Error (ERR_TPM_NV_INDEX_INVALID_PO_ATTR). I removed the
TPMA_NV_NO_DA flag and it ended up working. What would the correct solution
for this issue be?

The Policy Control field in the LCP has a field that specifies whether
the OS INIT DATA Capabilities should be extended or not. I tried changing
that field in my PO LCP, but that didn't make a difference: the capabilites
are always extended, regardless of the value in the field. I can see that
my Policy is being read by checking the TPM Event log (type 0x414 tells me
that my index is being read, and type 0x40c shows that my policy control is
being loaded). I was playing with this to see the effect of changing things
in the policy.

These are minor issues that I are not blocking me, but I would like to get
an answer to better understand how TXT works.

Best Regards,
Marco

On Tue, May 23, 2017 at 5:12 PM, Sun, Ning <nin...@in...> wrote:

> Hi Marco,
>
>
>
> Thanks for the write-up, you got most of the answers correct for your
> questions.
>
>
>
> Both lcptools and lcptools-v2 folders (in tboot source package) are for
> LCP V2 on TPM 1.2 platforms
>
>
>
> Folder lcp-gen2 is for LCP V3 creation on TPM 2.0 platform, so far tboot
> does not provide tpm 2.0 tools to write the LCP to TPM nv index, there are
> TPM 2.0 TSS and tools from Intel as well, see below.
>
>
>
> For tboot VLP, there is a default VLP in tboot source code, if there is no
> VLP found from TPM NV index, tboot will apply the default VLCP.
>
>
>
> For TPM 2.0 TSS and tools, here are the website for your reference:
>
>
>
> https://github.com/01org/TPM2.0-TSS
>
>
>
> https://github.com/01org/tpm2.0-tools
>
>
>
> -Ning
>
>
>
> *From:* Marco Vanotti [mailto:mva...@go...]
> *Sent:* Tuesday, May 23, 2017 1:32 PM
> *To:* tbo...@li...
> *Subject:* Re: [tboot-devel] Questions about Launch Control Policies
>
>
>
> Hi All!
>
>
>
> After reading a lot of documentation [*], I think I figured out the
> answers to some of the questions. I would like to confirm if what I think
> is correct.
>
>
>
> TBOOT sets up an environment and executes GETSEC[SENTER], which handles
> control over to the SINIT ACM. The SINIT ACM will measure the MLE and
> execute the policy engine, which validates the LCPs. The ACM will extend
> the MLE hash to PCR17 among other things.  After that, the ACM will handle
> control back to TBOOT, which will execute the post_launch mechanism. There,
> it will look for VLCPs, first in a special NV Index (0x01200001 or
> 0x01c10131), or as a LCP_CUSTOM_ELEMENT in the policy data file, and then
> validates it.
>
>
>
> For remote attestation, you would want to get PCR17 and PCR18, maybe PCR0
> to make sure that BIOS is still the same? What I find unclear is how one
> should handle updates, BIOS, Kernel and TBOOT. It seems like the best way
> is to have a replicated setup for testing the updates and do all the
> measurements there.
>
>
>
> ---------------------------
>
>
>
> The problem with the NV Indices that I had (index 0x1400001 was being
> deleted on every reboot) was a BIOS issue. I contacted the platform
> supplier and asked for a BIOS update.
>
>
>
> The way to check which set of indices are used by your ACM is by checking
> the *tpm_nv_index_set* under the TPM capabilities in the loaded SINIT ACM
> (tables A-8 and A-9 from the intel txt guide, in Appendix A). The NVRAM
> Indices and attributes can be found in the Table J-2 (Appendix J TPM NV).
> For example, it says that the LCP PO index is 0x1400001 or 0x1c10106
> (depending on the tpm_nv_index_set).
>
>
>
> I have more questions, but I will try to write another email for them, as
> they are not related to this problem.
>
>
>
> Thank you all for your time :)
>
>
>
> Best Regards,
> Marco
>
>
>
> [*]:
>
> Intel TXT Software Development Guide: http://www.intel.com/co
> ntent/www/us/en/software-developers/intel-txt-software-devel
> opment-guide.html
>
> TPM 2.0 Spec: https://trustedcomputinggroup.org/tpm-library-specification/
>
> A practical guide to TPM 2.0: http://www.apress.com/us/book/9781430265832
>
> Intel Trusted Execution for Server Platforms: http://www.apress.c
> om/us/book/9781430261483
>
> TPM 2.0 registry of reserved handles: https://trustedcomput
> inggroup.org/registry-reserved-tpm-2-0-handles-localities/
>
>
>
> On Thu, May 4, 2017 at 7:19 PM, Marco Vanotti <mva...@go...> wrote:
>
> Hi All!
>
>
>
> I hope you are having a wonderful day today :). I am trying to get tboot
> to work in my machine. My computer has a TPM 2.0 and I am trying to
> understand some of the available features.
>
>
>
> The Intel TXT Software Development Guide defines Launch Control Policies.
> Given that I have TPM 2.0, I believe I should use version 3.0 or 3.1, there
> seem to be some utilities to write these files in the lcp-gen2 folder.
>
>
>
> Looking at the source code, I found that there's also TBOOT Control
> Policies, which seem to be referred as Verified Launch Control Policies.
> What is the difference between them? When should I use each of them? Are
> they also executed by the ACM? if not, when?
>
>
>
> It seems that VLCPs don't support policy data files, is that so?
>
>
>
> Regarding LCPs, where should I define them in NVRAM? I've tried using
> 0x1400001, but that index gets deleted every time I reboot the system,
> regardless of using TXT. I'm defining the space with attr 0xF00F, and size
> 102 bytes, which is the size of the lcp_policy_2 struct. There's another
> index to use that doesn't get deleted: 0x01c10106, but I am not sure how to
> tell TXT to use it.
>
>
>
> My original goal was to install a policy with POLTYPE_ANY, just to test,
> but I can't see anything related to it in txt-stat, should it be logged
> somehow?
>
>
>
> Any help with these issues would be really appreciated :)
>
>
>
> Best Regards,
> Marco
>
>
>