Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934286AbdCWOfO (ORCPT ); Thu, 23 Mar 2017 10:35:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57416 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754428AbdCWOfK (ORCPT ); Thu, 23 Mar 2017 10:35:10 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 54637C0528B5 Authentication-Results: ext-mx07.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx07.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=david@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 54637C0528B5 From: David Hildenbrand To: kvm@vger.kernel.org Cc: Paolo Bonzini , rkrcmar@redhat.com, Dmitry Vyukov , Marcelo Tosatti , stable@vger.kernel.org, LKML , david@redhat.com Subject: [PATCH v1] KVM: kvm_io_bus_unregister_dev() should never fail Date: Thu, 23 Mar 2017 15:34:41 +0100 Message-Id: <20170323143441.5749-1-david@redhat.com> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Thu, 23 Mar 2017 14:34:47 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4891 Lines: 152 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@vger.kernel.org # 3.4+ Reported-by: Dmitry Vyukov Signed-off-by: David Hildenbrand --- Based on kvm/queue, where we just got 2a108a4e7c1 ("KVM: x86: clear bus pointer when destroyed"), which added a check we need here. --- include/linux/kvm_host.h | 4 ++-- virt/kvm/kvm_main.c | 39 +++++++++++++++++++++++---------------- 2 files changed, 25 insertions(+), 18 deletions(-) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 2c14ad9..d025074 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/kvm_main.c b/virt/kvm/kvm_main.c index 7445566..e1be4b4 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -3476,6 +3476,8 @@ 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 +3495,8 @@ 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 +3547,8 @@ 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 +3561,9 @@ 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 +3583,41 @@ 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 +3630,8 @@ 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) -- 2.9.3