linux-kernel - Re: [PATCH v2 2/3] efi: call get_event

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Date:   Mon, 18 Sep 2017 14:28:45 +0200
From:   Thiebaud Weksteen <tweek@...gle.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Matthew Garrett <mjg59@...gle.com>, linux-efi@...r.kernel.org,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        linux-kernel@...r.kernel.org, tpmdd-devel@...ts.sourceforge.net,
        peterhuewe@....de,
        Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        tpmdd@...horst.net
Subject: Re: [PATCH v2 2/3] efi: call get_event_log before ExitBootServices

On Thu, Sep 14, 2017 at 9:02 PM, Jarkko Sakkinen
<jarkko.sakkinen@...ux.intel.com> wrote:
> On Thu, Sep 14, 2017 at 11:48:54AM -0700, Matthew Garrett wrote:
>> On Thu, Sep 14, 2017 at 11:43 AM, Jarkko Sakkinen
>> <jarkko.sakkinen@...ux.intel.com> wrote:
>> > On Mon, Sep 11, 2017 at 12:00:21PM +0200, Thiebaud Weksteen wrote:
>> >> With TPM 2.0 specification, the event logs may only be accessible by
>> >> calling an EFI Boot Service. Modify the EFI stub to copy the log area to
>> >> a new Linux-specific EFI configuration table so it remains accessible
>> >> once booted.
>> >>
>> >> When calling this service, it is possible to specify the expected format
>> >> of the logs: TPM 1.2 (SHA1) or TPM 2.0 ("Crypto Agile"). For now, only the
>> >> first format is retrieved.
>> >>
>> >> Signed-off-by: Thiebaud Weksteen <tweek@...gle.com>
>> >
>> > With a quick skim the code change looks good but I remember from
>> > Matthew's talk that there was this issue that ExitBootServices() would
>> > cause a yet another event?
>> >
>> > I guess you could manually synthetize that event by reading the PCR
>> > values right after ExitBootServices()?
>>
>> I think that would involve breaking SHA1… the information should be
>
> You are absolutely right, was not thinking clearly :-)
>
>> available in the TCG_TREE_FINAL_EVENTS configuration table, so it
>> /should/ just be a matter of merging the events from that into the
>> event log.
>
> Right, it is available through runtime services. Why this isn't part
> of the patch set?

This is not included yet as this table
(EFI_TCG2_FINAL_EVENTS_TABLE_GUID) relies on the TPM2 format for the
log entries (TCG_PCR_EVENT2, "Crypto Agile"). I first plan to add the
parsing of this log version (ie, efi_retrieve_tpm2_eventlog_2) before
adding the merging of both tables. But these will be separate patch
sets.

>
> /Jrakko
>
> /Jarkko