Re: TPM support within Grub2

[Javier Martinez Canillas]

On 07/17/2018 06:57 PM, Philip Tricca wrote:
> On Mon, Jul 16, 2018 at 02:06:12PM +0200, Daniel Kiper wrote:
>> On Mon, Jul 02, 2018 at 06:35:08PM +0200, Daniel Kiper wrote:
>>> Hi Daniel,
>>>
>>> On Sun, Jul 01, 2018 at 07:09:30PM -0400, Daniel P. Smith wrote:
>>>> Greetings,
>>>>
>>>> I have a measured boot implementation I have been working on that
>>>> introduces a DRTM relocator that I would like to eventually upstream.
>>>> This work does rely on the ability to access a TPM 1.2 chip from within
>>>> Grub2. I am aware of Matthew Garrett's pending patch to add core TPM
>>>> support[1] but that is limited to UEFI environments. My target
>>>> environment uses Coreboot with the TCG BIOS payload to launch the
>>>> environment. For TPM support I am using code picked out of the
>>>> TrustedGRUB2 fork[2]. As a precursor to upstreaming my DRTM relocator, I
>>>> would like to see if I could find a way to generically introduce TPM
>>>> support into Grub2 that support's Matthew's UEFI backend, TrustedGrub2's
>>>> TPM 1.2 raw I/O, as well as leave a path for TPM2 raw I/O. In both
>>>> implementations TPM support is include as an x86 device when in fact
>>>> they can also be found in ARM devices, which is on my wish list of
>>>> future devices I would like to support. With all of this in mind, I
>>>> wanted to open a discussion on the best way to implement generic TPM
>>>> support. In Matthew's approach TPM is implemented under
>>>> grub-core/commands while TrustedGRUB2 is split between grub-core/kern
>>>> and grub-core/tpm. IMHO TPM functionality should be divided into HW
>>>> interfaces, TPM command processing, and higher order TPM operations. If
>>>> the logic was segmented in this manner, what are other's opinions on
>>>> where segments of logic should reside within the Grub2 source tree?
>>>>
>>>>
>>>> [1] http://lists.gnu.org/archive/html/grub-devel/2017-07/msg00005.html
>>>> [2] https://github.com/Rohde-Schwarz-Cybersecurity/TrustedGRUB2
>>
>> In general I am not against reorganization you are mentioning above.
>> Though I think that then you should rearange Matthew code and repost
>> it. Of course if Matthew does not object.
>>
>> Another thing is the verifiers framework. It would be nice if you could
>> hook your work there. Though you have to remember about other users like
>> UEFI secure boot 
>> (https://lists.xen.org/archives/html/xen-devel/2017-07/msg00985.html;
>> I am going to revive work on this patch) or GPG signatures. So, please
>> take a look at that code at git://git.savannah.gnu.org/grub.git,
>> phcoder/verifiers branch. If it works for you I will post the patches,
>> with minor fixes and improvements which are worth doing, for review (of
>> course if Vladimir does not object). If you discover any issues with the
>> verifiers framework just drop me a line and then we will try to fix them.
>>
>> And another thing... Could not we reuse Philip TPM 2.0 work in GRUB2 somehow?
> 
> It's possible to use at least one of the APIs we've been developing in
> Grub2 but I'm not sure the patches under review require this. It's been
> a year now since I've reviewed these patches but AFAIK they don't
> require any TPM2 functions beyond what the UEFI TrEE protocol exposes.
>

That's correct.
 
> I have had a few people ask about combining Grub2s support for LUKS
> volumes with the key usage policy from the TPM2 as a way to ensure the
> integrity of the firmware before releasing a key used to decrypt the
> LUKS volume. In this case using some of the APIs / libraries we've been
> developing (https://github.com/tpm2-software/tpm2-tss) would make sense
> since the TrEE protocol doesn't expose any of the interfaces we would
> require: key creation & loading, policy sessions etc.
> 
> There would be a small amout of development work to implement an adapter
> to sit between the tss2-sys library and the TrEE 'SubmitCommand'
> function though. We have a standard API for this and have used it as the
> basis for our support on Linux and Windows so I don't expect a UEFI
> implementation to be much work if it becomes necessary. I do not however
> believe this is required for the work under review.
>

I wonder if we want something like the System API in GRUB2 or just a set of
TPM2 commands implemented using the EFI_TCG2_SUBMIT_COMMAND as you said. Is
what Microsoft is doing in its lsvmload [0] to implement its Shielded VM [1].

The lsvmload is an EFI binary that's executed before the boot-loader and it
is used just to unseal a key to unlock an encrypted partition where the real
boot-loader is stored.

[0]: https://github.com/Microsoft/lsvmtools/blob/master/lsvmutils/tpm2.c
[1]: 
https://events.static.linuxfound.org/sites/events/files/slides/LinuxCon%20Mike%20Brasher.pdf

Something like this can also be built on top of Matthew's current patch-set.

> Regards,
> Philip
> 

Best regards,
-- 
Javier Martinez Canillas
Software Engineer - Desktop Hardware Enablement
Red Hat