On Fri, 08 Jul 2016 15:12:07 +0200 Greg Kurz <[email protected]> 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(). ======================================================================== > > Signed-off-by: Greg Kurz <[email protected]> > --- > 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; > > >
