On 30.03.2017 10:00, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
>
> The patch below does not apply to the 4.9-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@xxxxxxxxxxxxxxx>.
>
Hi,
just as for the 4.10-stable backport, this commit can be cleanly
cherry-picked after cherry-picking df630b8c1e85 ("KVM: x86: clear bus
pointer when destroyed") as a prerequisite.
Thanks!
> thanks,
>
> greg k-h
>
> ------------------ original commit in Linus's tree ------------------
>
> From 90db10434b163e46da413d34db8d0e77404cc645 Mon Sep 17 00:00:00 2001
> From: David Hildenbrand <david@xxxxxxxxxx>
> Date: Thu, 23 Mar 2017 18:24:19 +0100
> Subject: [PATCH] KVM: kvm_io_bus_unregister_dev() should never fail
>
> 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")
> Cc: stable@xxxxxxxxxxxxxxx # 3.4+
> Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Reviewed-by: Cornelia Huck <cornelia.huck@xxxxxxxxxx>
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 2c14ad9809da..d0250744507a 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -162,8 +162,8 @@ int kvm_io_bus_read(struct kvm_vcpu *vcpu, 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);
> struct kvm_io_device *kvm_io_bus_get_dev(struct kvm *kvm, enum kvm_bus bus_idx,
> gpa_t addr);
>
> diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
> index a29786dd9522..4d28a9ddbee0 100644
> --- a/virt/kvm/eventfd.c
> +++ b/virt/kvm/eventfd.c
> @@ -870,7 +870,8 @@ 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 7445566fadc1..ef1aa7f1ed7a 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -728,7 +728,8 @@ 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);
> @@ -3476,6 +3477,8 @@ int kvm_io_bus_write(struct kvm_vcpu *vcpu, enum kvm_bus bus_idx, gpa_t addr,
> };
>
> bus = srcu_dereference(vcpu->kvm->buses[bus_idx], &vcpu->kvm->srcu);
> + if (!bus)
> + return -ENOMEM;
> r = __kvm_io_bus_write(vcpu, bus, &range, val);
> return r < 0 ? r : 0;
> }
> @@ -3493,6 +3496,8 @@ int kvm_io_bus_write_cookie(struct kvm_vcpu *vcpu, enum kvm_bus bus_idx,
> };
>
> bus = srcu_dereference(vcpu->kvm->buses[bus_idx], &vcpu->kvm->srcu);
> + if (!bus)
> + return -ENOMEM;
>
> /* First try the device referenced by cookie. */
> if ((cookie >= 0) && (cookie < bus->dev_count) &&
> @@ -3543,6 +3548,8 @@ int kvm_io_bus_read(struct kvm_vcpu *vcpu, enum kvm_bus bus_idx, gpa_t addr,
> };
>
> bus = srcu_dereference(vcpu->kvm->buses[bus_idx], &vcpu->kvm->srcu);
> + if (!bus)
> + return -ENOMEM;
> r = __kvm_io_bus_read(vcpu, bus, &range, val);
> return r < 0 ? r : 0;
> }
> @@ -3555,6 +3562,9 @@ 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;
> @@ -3574,45 +3584,41 @@ 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 = kmalloc(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;
> }
>
> struct kvm_io_device *kvm_io_bus_get_dev(struct kvm *kvm, enum kvm_bus bus_idx,
> @@ -3625,6 +3631,8 @@ struct kvm_io_device *kvm_io_bus_get_dev(struct kvm *kvm, enum kvm_bus bus_idx,
> srcu_idx = srcu_read_lock(&kvm->srcu);
>
> bus = srcu_dereference(kvm->buses[bus_idx], &kvm->srcu);
> + if (!bus)
> + goto out_unlock;
>
> dev_idx = kvm_io_bus_get_first_dev(bus, addr, 1);
> if (dev_idx < 0)
>
--
Thanks,
David