On Fri, Jul 08, 2016 at 05:47:01PM +0200, Greg Kurz wrote: > On Fri, 08 Jul 2016 15:12:07 +0200 > Greg Kurz <gr...@kaod.org> wrote: > > > If the host has 8 threads/core and the guest is started with: > > > > -smp cores=1,threads=4,maxcpus=12 > > > > It is possible to crash QEMU by doing: > > > > (qemu) device_add host-spapr-cpu-core,core-id=16,id=foo > > (qemu) device_del foo > > Segmentation fault > > > > This is caused because spapr_core_unplug() assumes cpu_dt_id == core_id. > > Even if it happens to be the case when the host and guest have the same > > number of threads per core, it is conceptually wrong and we may pass a > > bogus id to spapr_dr_connector_by_id() and spapr_core_release() crashes. > > > > Let's use cc->core_id, which is the id that was used to create th DR > > connector. > > My bad, I got excited and pointed out the wrong culprit... it is cpu_index > again of course ! Please find an updated explanation to be put in the > changelog after "Segmentation fault": > > ======================================================================== > This happens because spapr_core_unplug() assumes cpu_dt_id == core_id. > As long as cpu_dt_id is derived from the non-table cpu_index, this is > only true when you plug cores with contiguous ids. > > It is safer to be consistent: the DR connector was created with an > index that is immediately written to cc->core_id, and spapr_core_plug() > also relies on cc->core_id. > > Let's use it also in spapr_core_unplug(). > ========================================================================
Reworded in place, thanks.
>
> >
> > Signed-off-by: Greg Kurz <gr...@kaod.org>
> > ---
> > hw/ppc/spapr_cpu_core.c | 6 ++----
> > 1 file changed, 2 insertions(+), 4 deletions(-)
> >
> > diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
> > index 70b6b0b5ee17..106eaf45b399 100644
> > --- a/hw/ppc/spapr_cpu_core.c
> > +++ b/hw/ppc/spapr_cpu_core.c
> > @@ -126,11 +126,9 @@ static void spapr_core_release(DeviceState *dev, void
> > *opaque)
> > void spapr_core_unplug(HotplugHandler *hotplug_dev, DeviceState *dev,
> > Error **errp)
> > {
> > - sPAPRCPUCore *core = SPAPR_CPU_CORE(OBJECT(dev));
> > - PowerPCCPU *cpu = POWERPC_CPU(core->threads);
> > - int id = ppc_get_vcpu_dt_id(cpu);
> > + CPUCore *cc = CPU_CORE(dev);
> > sPAPRDRConnector *drc =
> > - spapr_dr_connector_by_id(SPAPR_DR_CONNECTOR_TYPE_CPU, id);
> > + spapr_dr_connector_by_id(SPAPR_DR_CONNECTOR_TYPE_CPU, cc->core_id);
> > sPAPRDRConnectorClass *drck;
> > Error *local_err = NULL;
> >
> >
> >
>
--
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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