[Skiboot] [RFC PATCH 0/3] WIP VMM for OPAL boot

[Nicholas Piggin]

Stewart Smith's on June 7, 2019 7:56 am:
> Stewart Smith <stewart at linux.ibm.com> writes:
>> Nicholas Piggin <npiggin at gmail.com> writes:
>>> This is my current work in progress, I've gradually been adding bits
>>> and fixing bugs so time for another rebase. It's been booting pretty
>>> reliably on my P9, I've next been trying to bring VMM mode back up
>>> when we fast-reboot which is still a bit buggy but almost works.
>>
>> Cool. I'm chasing the secure boot problems, which has now become "get
>> all the genuine secure "rom" stuff running in Mambo".
>>
>> This is the most obivous "Something is going to go wrong without it" bit
>> I have, but that doesn't magically fix things, nor explain why
>> everything stops suddenly.
> 
> As mentioned on slack, I found the problem was that we had a "li %r2,0"
> in the mix.
> 
> The Container Verification Code is a blob that we get passed in from
> hostboot (well, all the way from the hostboot bootloader actually) that
> has two entry points: one for validating a secureboot header and the
> other for computing sha512 checksum of a blob.
> 
> In skiboot, the libstb/cvc.c code finds it, which on P9 is from a
> reserved memory region, and on P8 it's by copying it from an actual ROM
> that's on chip that needs to be accessed with cache inhibited reads.
> 
> The asm/cvc_entry.S wrapper, as part of calling the CVC function, sets
> %r2 to zero. Thus, when we take the ISI for the page of text, we end up
> in vm_isi() without %r2 set to anything sane, and we end up hitting the
> assert(!_dw0) in htab_install because we're poking around where we're
> not meant to. Naturally, all the (soon multiple levels) of
> exception_entry() and abort() without a sane %r2 goes about as well as
> you'd expect and we eventually xstop.
> 
> For at least a quick hack (I haven't thought about it beyond "hey, we're
> not using that register") I stashed the skiboot TOC in HSPRG0 and pulled
> it in in _exception.
> 
> So, the below patch is on top of this series that (at least in Mambo, I
> haven't tested on hardware yet), will run the CVC code and boot a
> kernel.

Awesome, that r2 clobber was a good catch.

I think we can make a separate patch that always loads up
the skiboot r2 in the exception path (preserving the original),
which will also prevent bad crashes anywhere else that r2 is
modified on purpose or by mistake.

> 
> I'm not sure what's up with my mambo tcl to ensure I get the
> references/size right for the CVC code in the device tree, so have
> quickly hacked around it with a if (size==0) size = 64*1024 in cvc.c
> (maybe the Masters of Mambo can enlighten me).

What are you doing there, is that creating a CVC blob that actually
runs when you boot mambo?

> 
> I'm almost interested to try and pull out the CVC code and use that
> rather than the "softrom" hack I put in a couple of years ago.
>