On Tue, Aug 06, 2024, Michal Luczaj wrote:
> On 8/6/24 00:56, Sean Christopherson wrote:
> > [...]
> > + /*
> > + * xa_store() should never fail, see xa_reserve() above. Leak the vCPU
> > + * if the impossible happens, as userspace already has access to the
> > + * vCPU, i.e. freeing the vCPU before userspace puts its file reference
> > + * would trigger a use-after-free.
> > + */
> > if (KVM_BUG_ON(xa_store(&kvm->vcpu_array, vcpu->vcpu_idx, vcpu, 0), kvm)) {
> > - r = -EINVAL;
> > - goto kvm_put_xa_release;
> > + mutex_unlock(&vcpu->mutex);
> > + return -EINVAL;
> > }
> >
> > /*
> > @@ -4302,6 +4310,7 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, unsigned long id)
> > */
> > smp_wmb();
> > atomic_inc(&kvm->online_vcpus);
> > + mutex_unlock(&vcpu->mutex);
> >
> > mutex_unlock(&kvm->lock);
> > kvm_arch_vcpu_postcreate(vcpu);
> > @@ -4309,6 +4318,7 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, unsigned long id)
> > return r;
> >
> > kvm_put_xa_release:
> > + mutex_unlock(&vcpu->mutex);
> > kvm_put_kvm_no_destroy(kvm);
> > xa_release(&kvm->vcpu_array, vcpu->vcpu_idx);
>
> Since we're handling the impossible, isn't the BUG_ON part missing
> mutex_unlock(&kvm->lock)?
Doh, yes.
