Re: [Qemu-devel] [PATCH] ppc: add host-serial and host-model machine attributes

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

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On Mon, Feb 04, 2019 at 10:10:05AM +0000, Daniel P. Berrangé wrote:
> On Mon, Feb 04, 2019 at 12:09:04PM +1100, David Gibson wrote:
> > On Sat, Feb 02, 2019 at 12:23:58AM +0530, P J P wrote:
> > > From: Prasad J Pandit <pjp@fedoraproject.org>
> > > 
> > > On ppc hosts, hypervisor shares following system attributes
> > > 
> > >   - /proc/device-tree/system-id
> > >   - /proc/device-tree/model
> > > 
> > > with a guest. This could lead to information leakage and misuse.[*]
> > > Add machine attributes to control such system information exposure
> > > to a guest.
> > > 
> > > [*] https://wiki.openstack.org/wiki/OSSN/OSSN-0028
> > > 
> > > Reported-by: Daniel P. Berrangé <berrange@redhat.com>
> > > Fix-suggested-by: Daniel P. Berrangé <berrange@redhat.com>
> > > Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> > 
> > Hm.  This seems like it might be overkill.  I mean, obviously we need
> > to not leak that host information, but it's not clear we really need
> > these properties at all.  They're not specified in PAPR (contrary to
> > my previous guess) and it's not clear what actually uses them.
> > 
> > I'm wondering if we can just ditch them entirely, or at least make
> > them default to not present without regard to machine version.
> > 
> > Yes, that's technically a compatibility breaking change, but it's hard
> > to see anything that actually relied on these as not being broken
> > already, so I think that's actually a fair trade off for the security
> > improvement here.
> 
> We cannot assume that no one is using it.
> 
> In fact this issue came to light precisely because a person on IRC
> was asking why x86 couldn't provide the same info as PPC, because
> they found it useful on PPC.

"Found it useful" is not the same as actually relying on.

> So we will definitely break people if we remove this from existing
> VMs.

I don't think that follows from the information you've presented so
far.

-- 
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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