RE: [Xen-devel] [RFC][PATCH][0/2] Intel(r) Trusted Execution Technology support: Overview

["Cihula, Joseph" <joseph.cihula@xxxxxxxxx>]

Jun Koi <mailto:junkoi2004@xxxxxxxxx> scribbled on Wednesday, June 13,
2007 9:06 PM:
> On 6/14/07, Cihula, Joseph <joseph.cihula@xxxxxxxxx> wrote:
>> Jun Koi <mailto:junkoi2004@xxxxxxxxx> scribbled on Wednesday, June
>> 13, 2007 2:29 AM:
>>> Hi Joseph,
>>> 
>>> On 6/9/07, Cihula, Joseph <joseph.cihula@xxxxxxxxx> wrote:
>>>> Attached is a preliminary patch that adds Intel(r) Trusted
>>>> Execution Technology (Intel(r) TXT) support to Xen.  Intel(r) TXT
>>>> was formerly known by the codename LaGrande Technology (LT).
>>>> 
>>>> This version of the patch (the previous version was posted last
>>>> year) re-factors the Intel(r) TXT code into a separate
>>>> module/binary that is passed as the 'kernel' to GRUB and which
>>>> then launches Xen itself (after having performed the measured
>>>> launch). 
>>>> 
>>>> This patch supports all of the Xen processor modes
>>>> (32bit/32bitPAE/64bit) and supports multi-core/thread systems.  It
>>>> will run on either an Intel LT SDV3 or on the Intel(r) TXT TEP
>>>> (Technology Enabling Platform) from MPC.
>>>> 
>>>> 
>>>> Intel(r) TXT in Brief:
>>>> ----------------------
>>>> o  Provides dynamic root of trust for measurement (DRTM)
>>>> o  DMA protection (on SDV3/TEP platforms only)
>>>> o  Data protection in case of improper shutdown
>>>> 
>>>> For more information, see
>>>> http://www.intel.com/technology/security/. This site also has a
>>>> link to the Intel(r) TXT Preliminary Architecture Specification. 
>>>> 
>>>> 
>>>> Overview of Patch Functionality:
>>>> --------------------------------
>>>> o  Measured Launch.  If the processor is detected as being
>>>> TXT-capable and enabled then the code will attempt to perform a
>>>> measured launch.  If the measured launch process fails (processor
>>>> is not capable, TXT is not enabled, missing SINIT, corrupted data,
>>>> etc.)) then it will fall-through to a non-TXT boot of Xen.
>>>> 
>>> 
>>> This is interesting. Do I understand correctly as in below?
>>> 
>>> - sboot runs in VMX root-operation, then it boots Xen. Then Xen is
>>> in non-root operation.
>> 
>> Not exactly.  Only the APs get put into VMX mode and this is so they
>> can respond to the INIT-SIPI-SIPI SMP boot sequence; and then VMX is
>> turned off after they are awakened.  The BSP does not enable VMX
>> until Xen enables it. 
>> 
>>> - After that, Xen switches back to root-operation. Life goes on as
>>> it is now. 
>>> 
>>> If that is the case, then Xen can access the reserved memory by
>>> sboot, right? So in case Xen is compromised, the secrets saved in
>>> the reserved memory can be leaked?
>> 
>> This is correct, however.  sboot and Xen are in the same protection
>> domain.  Since VT does not support nested/recursive virtualization,
>> there is really no way to protect sboot from Xen.  But I don't see
>> this as a problem either.  sboot does not have any secrets (at least
>> not at this time) and could just as easily have been a part of Xen
>> (it was in the last year's patch) if we didn't want to generalize it.
>> 
>>> Perhaps I understand something wrong, as the whole things dont make
>>> sense to me.
>> 
>> The best way to think of Intel(r) TXT is as a technology that
>> provides a dynamic (i.e. at the time it is invoked) root of trust,
>> or "safe place to stand".  So it allows you to start some code in a
>> "secure"/measured environment and then that code can establish any
>> further protections it needs. 
>> 
>>> 
> 
> Thanks! Certainly I need to look at TXT spec.
> 
> A question: can /proc/cpuinfo tell me my machine has TXT enabled? If
> not, is there any way to detect TXT from Linux without inspecting BIOS
> setup?

/proc/cpuinfo will only tell you if a CPU supports the SMX (GETSEC)
instructions.  It will not tell you if the chipset is TXT-capable nor
whether TXT is enabled.  If you look at the code in sboot/txt/verify.c
you can see how the supports_smx() function determines if the CPU both
supports and is enabled for TXT.  supports_txt() shows how to determine
that the chipset supports it.

> Same question for TPM.

I belive that you can use the ACPI tables to determine if a TPM is
supported.  You can also query it using it's fixed MMIO registers.

> 
> Thanks,
> Jun

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