Re: [Qemu-devel] [Qemu-ppc] [PATCH v2] spapr-rtas: add ibm, get-vpd RTAS interface

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Feb 27, 2019 at 12:04:49PM -0300, Murilo Opsfelder Araujo wrote:
> Hi, David.
> 
> On Wed, Feb 27, 2019 at 10:19:20AM +1100, David Gibson wrote:
> > On Tue, Feb 26, 2019 at 04:11:40PM -0300, Murilo Opsfelder Araujo wrote:
> > > On Tue, Feb 26, 2019 at 02:08:30PM -0300, Murilo Opsfelder Araujo wrote:
> > > > Hi, Maxiwell.
> > > >
> > > > On Tue, Feb 26, 2019 at 11:21:26AM -0300, Maxiwell S. Garcia wrote:
> > > > > On Tue, Feb 26, 2019 at 02:21:03PM +1100, David Gibson wrote:
> > > > > > On Mon, Feb 25, 2019 at 08:20:09PM -0300, Murilo Opsfelder Araujo wrote:
> > > > > > > Hi, Maxiwell.
> > > > > > >
> > > > > > > On Mon, Feb 25, 2019 at 01:23:25PM -0300, Maxiwell S. Garcia wrote:
> > > > > > > > This adds a handler for ibm,get-vpd RTAS calls, allowing pseries
> > > > > > > > guest to collect host information. It is disabled by default to
> > > > > > > > avoid unwanted information leakage. To enable it, use:
> > > > > > > > ‘-M pseries,vpd-export=on’
> > > > > > >
> > > > > > > The patch for setting host-serial and host-model already landed Gibson's
> > > > > > > ppc-for-4.0 branch:
> > > > > > >
> > > > > > >   commit 9e584f45868f6945c1282c938278038cba0e4af2
> > > > > > >   Author: Prasad J Pandit <pjp@fedoraproject.org>
> > > > > > >   Date:   Mon Feb 18 23:43:49 2019 +0530
> > > > > > >
> > > > > > >       ppc: add host-serial and host-model machine attributes (CVE-2019-8934)
> > > > > > >
> > > > > > >
> > > > > > > QEMU should only return host-serial and host-model from the host if the
> > > > > > > following combination of parameters are provided:
> > > > > > >
> > > > > > >   -M host-serial=passthrough,host-model=passthrough,vpd-export=on
> > > > > > >
> > > > > > > If host-serial or host-model are set with a user-string, ibm,get-vpd should
> > > > > > > honor these values and return them, not exposing host information by accident.
> > > > > > >
> > > > > > > I'm not even sure if we need vpd-export=<bool> setting. Its logic could be
> > > > > > > derived from the presence of host-serial=passthrough and host-model=passthrough
> > > > > > > options.
> > > > > > >
> > > > > > > What do you think?
> > > > > >
> > > > > > That's an excellent point - I hadn't thought through the fact that
> > > > > > this is the same information exposed by those properties.  I do indeed
> > > > > > think that exposing the same information set in those properties - and
> > > > > > thereby avoiding the new machine option - would be a better plan.
> > > > > >
> > > > >
> > > > > I saw that the patch was applied. So I will work in another patch
> > > > > to use these properties and remove the export-vpd option.
> > > > >
> > > > > Another thing that I thought the fact that 'host-serial' and 'host-model'
> > > > > nodes in Device Tree are not in accordance with LoPAPR document. What
> > > > > you think in use only get-vpd to get these information and remove
> > > > > nodes from device tree?
> > > >
> > > > Both "system-id" and "model" properties are described in the section "3.3.2.1
> > > > Root Node Properties" of the "Device Tree Bindings: Linux on Power Architecture
> > > > Reference" document:
> > > >
> > > >   https://members.openpowerfoundation.org/wg/SYSSW/document/1455
> > >
> > > I replied too early. As Maxiwell explained to me (thanks Max!), guest can end up
> > > having the following entries under /proc/device-tree/ (among other entries):
> > >
> > >   $ cat host-serial
> > >   12A3B4C
> > >
> > >   $ cat host-model
> > >   1234-56A
> > >
> > >   $ cat system-id
> > >   c7b62da9-3d0c-44f9-8edb-2318271f3c1a
> > >
> > >   $ cat model
> > >   IBM pSeries (emulated by qemu)
> > >
> > > Where:
> > >
> > >   - host-serial/host-model: depend on "-M host-serial" and "-M host-model"
> > >     machine options.
> > >
> > >   - system-id: created when "-uuid <val>" exists in qemu command line options.
> > >
> > >   - model: hard-coded.
> > >
> > > With this patch, RTAS ibm,get-vpd call will return "system-id" and "model" from
> > > the host, not from the guest. I found this confusing.
> >
> > Hrm.  I found the bit in LoPAPR describing how ibm,get-vpd operates,
> > but not something describing the actual data that appears within it.
> > Where's that described?  It'd be nice to check if those values are
> > supposed to be describing the host or the guest.
> 
> Are you asking about the fields of the ibm,vpd property? They are described in
> Table 11.2 "LoPAPR VPD Fields" of this LoPAPR document:
> 
>   https://members.openpowerfoundation.org/wg/SYSSW/document/1461

That document appears to be only available to openpower members, which
I'm not.

I found Table 160 in my copy of LoPAPR (1.1) though, which looks like
it has the same stuff.  I wonder if I should be trying to get a more
recent LoPAPR.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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