Re: [tboot-devel] SENTER -> Legacy Shutdown

[Hal F. <hal...@gm...>]

Hi Jon - I have been working on something similar as a personal
experiment. I have successfully launched a measured environment from a
Linux device driver. It took a lot of trial and error to make it work.
On my machine, an HP dc7800, the LT.ERRORCODE register is not readable
after a TXT failure (the machine hangs and has to be power cycled) so
that made it somewhat more difficult.

Some advice I can suggest. I changed the BIOS to use only one CPU, and
then booted the single-CPU version of Linux. I don't know if downing
the CPUs from within Linux would accomplish the same thing, I haven't
tried that yet. (I am still working on returning from the measured
state back into Linux, which almost/sometimes works.) You might
consider doing this to remove one of the variables.

To make sure I recognized when I finally succeeded, I had my MLE start
with a jump to itself, an infinite loop. This was distinguishable from
the usual halt state because the display stayed on, and made sure that
I didn't have a successful launch which then failed due to something
in the MLE.

 As far as making it work, in the end it came down to careful study of
the TXT manual and attempting to verify that I had everything set up
correctly, especially the MTRRs and the page tables.

I have a smaller memory so my sinit is at 3e500000, size 5f00. Here is
how my MTRRs are set up:

MTRRCAP: 0xd08
MTRR_DEF_TYPE: 0x400
Variable MTRR Base 0: 0x3e500006, Mask: 0xfffffc800
Variable MTRR Base 1: 0x3e504006, Mask: 0xfffffe800
Remaining variable MTRRs are 0

My MLE on this run was at 0x20e00000 physical address. I put the MLE
page table at the beginning of this area:

PDPTE[0] = 0x20e01001
PDE[0] = 09x20e02003
PTE[0] = 0x20e03003
PTE[1] = 0x20e04003
PTE[2] = 0x20e05003

I loaded the MLE code at 0x20e03000 and put the MLE header at the
beginning. MLEPageTableBase was 0x20e00000. PMRLowBase is the MLE
address rounded down to a 2MB boundary; PMRLowSize is 2 MB.
MLEHeaderBase is 0 (the "virtual" address of the MLE header using the
MLE page tables).

Hopefully some of this might give you some ideas of things to try -

Hal Finney