On Wed, Mar 15, 2017 at 10:19:53AM +0100, David Hildenbrand wrote: > Am 15.03.2017 um 07:24 schrieb Peter Xu: > > On Tue, Mar 14, 2017 at 02:34:29PM +0100, David Hildenbrand wrote: > >> Avoid races between KVM_SET_GSI_ROUTING and KVM_CREATE_IRQCHIP by taking > >> the kvm->lock when setting up routes. > >> > >> If KVM_CREATE_IRQCHIP fails, KVM_SET_GSI_ROUTING could have already set > >> up routes pointing at pic/ioapic, being silently removed already. > >> > >> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> > >> --- > >> virt/kvm/kvm_main.c | 3 +++ > >> 1 file changed, 3 insertions(+) > >> > >> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > >> index a17d787..ad0f8b2 100644 > >> --- a/virt/kvm/kvm_main.c > >> +++ b/virt/kvm/kvm_main.c > >> @@ -3079,8 +3079,11 @@ static long kvm_vm_ioctl(struct file *filp, > >> routing.nr * sizeof(*entries))) > >> goto out_free_irq_routing; > >> } > >> + /* avoid races with KVM_CREATE_IRQCHIP on x86 */ > >> + mutex_lock(&kvm->lock); > >> r = kvm_set_irq_routing(kvm, entries, routing.nr, > >> routing.flags); > >> + mutex_unlock(&kvm->lock); > >> out_free_irq_routing: > >> vfree(entries); > >> break; > >> -- > >> 2.9.3 > >> > > > > Out of my curiousity: do we have a use case that these two operations > > might collapse (KVM_CREATE_IRQCHIP and KVM_SET_GSI_ROUTING)? Or is > > this patch only for the sake of security? > > Just for the sake of security. I think, in general such calls are not > supposed to be done in parallel. But of course, user space can. I see. > > > > > Another thing to mention is that, I guess adding this lock will > > benefit KVM_CAP_SPLIT_IRQCHIP as well, maybe nice to mention it too in > > the commit message. No worth a repost for this single reason though. > > > > I added > > "Also, as a side effect, this patch makes sure that KVM_SET_GSI_ROUTING > and KVM_CAP_SPLIT_IRQCHIP cannot run in parallel." Yeah it looks better. Thanks! -- peterx
