KVM: kvm_io_bus_unregister_dev() should never fail

commit 90db10434b163e46da413d34db8d0e77404cc645 upstream.

No caller currently checks the return value of
kvm_io_bus_unregister_dev(). This is evil, as all callers silently go on
freeing their device. A stale reference will remain in the io_bus,
getting at least used again, when the iobus gets teared down on
kvm_destroy_vm() - leading to use after free errors.

There is nothing the callers could do, except retrying over and over
again.

So let's simply remove the bus altogether, print an error and make
sure no one can access this broken bus again (returning -ENOMEM on any
attempt to access it).

Fixes: e93f8a0f821e ("KVM: convert io_bus to SRCU")
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index e4d8f705fecd0ae2657a66d6524fd4463fb38f1f..aa75be9cbc3d4d9a9b60b2d6845929c01b987031 100644 (file)
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -177,8 +177,8 @@ int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr, int len,
                    void *val);
 int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
                            int len, struct kvm_io_device *dev);
-int kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
-                             struct kvm_io_device *dev);
+void kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
+                              struct kvm_io_device *dev);
 
 #ifdef CONFIG_KVM_ASYNC_PF
 struct kvm_async_pf {

diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 5a310caf4bbe6c12ae9a6c2146b0310ef1c9fde1..64238c9c5dcedf792f067d6cb3bbd9cc4875376c 100644 (file)
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -866,7 +866,8 @@ kvm_deassign_ioeventfd_idx(struct kvm *kvm, enum kvm_bus bus_idx,
                        continue;
 
                kvm_io_bus_unregister_dev(kvm, bus_idx, &p->dev);
-               kvm->buses[bus_idx]->ioeventfd_count--;
+               if (kvm->buses[bus_idx])
+                       kvm->buses[bus_idx]->ioeventfd_count--;
                ioeventfd_release(p);
                ret = 0;
                break;

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5f7bff5b9e4e9ad5dc7b32f33c1cc5ee66b48b93..3d5ae6f655dfc4a4970f8f0bd5b7d56a8d08b772 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -615,7 +615,8 @@ static void kvm_destroy_vm(struct kvm *kvm)
        spin_unlock(&kvm_lock);
        kvm_free_irq_routing(kvm);
        for (i = 0; i < KVM_NR_BUSES; i++) {
-               kvm_io_bus_destroy(kvm->buses[i]);
+               if (kvm->buses[i])
+                       kvm_io_bus_destroy(kvm->buses[i]);
                kvm->buses[i] = NULL;
        }
        kvm_coalesced_mmio_free(kvm);
@@ -2980,6 +2981,8 @@ int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
        };
 
        bus = srcu_dereference(kvm->buses[bus_idx], &kvm->srcu);
+       if (!bus)
+               return -ENOMEM;
        r = __kvm_io_bus_write(bus, &range, val);
        return r < 0 ? r : 0;
 }
@@ -2997,6 +3000,8 @@ int kvm_io_bus_write_cookie(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
        };
 
        bus = srcu_dereference(kvm->buses[bus_idx], &kvm->srcu);
+       if (!bus)
+               return -ENOMEM;
 
        /* First try the device referenced by cookie. */
        if ((cookie >= 0) && (cookie < bus->dev_count) &&
@@ -3047,6 +3052,8 @@ int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
        };
 
        bus = srcu_dereference(kvm->buses[bus_idx], &kvm->srcu);
+       if (!bus)
+               return -ENOMEM;
        r = __kvm_io_bus_read(bus, &range, val);
        return r < 0 ? r : 0;
 }
@@ -3059,6 +3066,9 @@ int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
        struct kvm_io_bus *new_bus, *bus;
 
        bus = kvm->buses[bus_idx];
+       if (!bus)
+               return -ENOMEM;
+
        /* exclude ioeventfd which is limited by maximum fd */
        if (bus->dev_count - bus->ioeventfd_count > NR_IOBUS_DEVS - 1)
                return -ENOSPC;
@@ -3078,45 +3088,41 @@ int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
 }
 
 /* Caller must hold slots_lock. */
-int kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
-                             struct kvm_io_device *dev)
+void kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
+                              struct kvm_io_device *dev)
 {
-       int i, r;
+       int i;
        struct kvm_io_bus *new_bus, *bus;
 
        bus = kvm->buses[bus_idx];
-
-       /*
-        * It's possible the bus being released before hand. If so,
-        * we're done here.
-        */
        if (!bus)
-               return 0;
+               return;
 
-       r = -ENOENT;
        for (i = 0; i < bus->dev_count; i++)
                if (bus->range[i].dev == dev) {
-                       r = 0;
                        break;
                }
 
-       if (r)
-               return r;
+       if (i == bus->dev_count)
+               return;
 
        new_bus = kzalloc(sizeof(*bus) + ((bus->dev_count - 1) *
                          sizeof(struct kvm_io_range)), GFP_KERNEL);
-       if (!new_bus)
-               return -ENOMEM;
+       if (!new_bus)  {
+               pr_err("kvm: failed to shrink bus, removing it completely\n");
+               goto broken;
+       }
 
        memcpy(new_bus, bus, sizeof(*bus) + i * sizeof(struct kvm_io_range));
        new_bus->dev_count--;
        memcpy(new_bus->range + i, bus->range + i + 1,
               (new_bus->dev_count - i) * sizeof(struct kvm_io_range));
 
+broken:
        rcu_assign_pointer(kvm->buses[bus_idx], new_bus);
        synchronize_srcu_expedited(&kvm->srcu);
        kfree(bus);
-       return r;
+       return;
 }
 
 static struct notifier_block kvm_cpu_notifier = {