From patchwork Mon Aug 28 04:42:29 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paul Mackerras X-Patchwork-Id: 9924143 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 2E2F260329 for ; Mon, 28 Aug 2017 04:42:54 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 1E574285F0 for ; Mon, 28 Aug 2017 04:42:54 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 1318428640; Mon, 28 Aug 2017 04:42:54 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id CBA63285F0 for ; Mon, 28 Aug 2017 04:42:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751191AbdH1Eme (ORCPT ); Mon, 28 Aug 2017 00:42:34 -0400 Received: from ozlabs.org ([103.22.144.67]:48009 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751177AbdH1Emd (ORCPT ); Mon, 28 Aug 2017 00:42:33 -0400 Received: by ozlabs.org (Postfix, from userid 1003) id 3xgfJR5fNNz9s9Y; Mon, 28 Aug 2017 14:42:31 +1000 (AEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ozlabs.org; s=201707; t=1503895351; bh=9xLWyDRG3Wc7dvWeZgiUXrBcfjL8HhlSwnm4XWw43i8=; h=Date:From:To:Cc:Subject:From; b=KN0uFswsSiVGvmfRqi9cv3Vy3d+uud+W0N9eb1ig/ahdTu0ZltQO7c/8rVyV+9GQg 9pPnkFkSjmYLxc206dZ1dJux5+Zz0woQh501W3rB7lsT/8suQHQ6xfbtXcsolrjryN JX3u1lDg+RinF5eRIQOalPnL3rbiKtX14F81u2bkRYlYyZG576NjigLuQoi27Jng+B EjrJutFf5aoChQL5wximirtYAEsN/oypWjSXI0SNepTra1GaXPgfGRF9eEuOgj6gCg c0KXXVe8HJup1bikRw2TJss+CBkJLs5Mw7cvSSygLJMB3SZpbcyMdbHqZcjbaQv0HN SKdnSWtjUkhBw== Date: Mon, 28 Aug 2017 14:42:29 +1000 From: Paul Mackerras To: kvm-ppc@vger.kernel.org, kvm@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Cc: nixiaoming , David Hildenbrand , David Gibson , Al Viro Subject: [PATCH] KVM: PPC: Book3S HV: Protect updates to spapr_tce_tables list Message-ID: <20170828044228.GB12629@fergus.ozlabs.ibm.com> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.5.24 (2015-08-30) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Al Viro pointed out that while one thread of a process is executing in kvm_vm_ioctl_create_spapr_tce(), another thread could guess the file descriptor returned by anon_inode_getfd() and close() it before the first thread has added it to the kvm->arch.spapr_tce_tables list. That highlights a more general problem: there is no mutual exclusion between writers to the spapr_tce_tables list, leading to the possibility of the list becoming corrupted, which could cause a host kernel crash. To fix the mutual exclusion problem, we add a mutex_lock/unlock pair around the list_del_rce in kvm_spapr_tce_release(). Also, this moves the call to anon_inode_getfd() inside the region protected by the kvm->lock mutex, after we have done the check for a duplicate LIOBN. This means that if another thread does guess the file descriptor and closes it, its call to kvm_spapr_tce_release() will not do any harm because it will have to wait until the first thread has released kvm->lock. The other things that the second thread could do with the guessed file descriptor are to mmap it or to pass it as a parameter to a KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE ioctl on a KVM device fd. An mmap call won't cause any harm because kvm_spapr_tce_mmap() and kvm_spapr_tce_fault() don't access the spapr_tce_tables list or the kvmppc_spapr_tce_table.list field, and the fields that they do use have been properly initialized by the time of the anon_inode_getfd() call. The KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE ioctl calls kvm_spapr_tce_attach_iommu_group(), which scans the spapr_tce_tables list looking for the kvmppc_spapr_tce_table struct corresponding to the fd given as the parameter. Either it will find the new entry or it won't; if it doesn't, it just returns an error, and if it does, it will function normally. So, in each case there is no harmful effect. Signed-off-by: Paul Mackerras Reviewed-by: David Gibson --- arch/powerpc/kvm/book3s_64_vio.c | 21 ++++++++++----------- 1 file changed, 10 insertions(+), 11 deletions(-) diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c index 53766e2..8f2da8b 100644 --- a/arch/powerpc/kvm/book3s_64_vio.c +++ b/arch/powerpc/kvm/book3s_64_vio.c @@ -265,8 +265,11 @@ static int kvm_spapr_tce_release(struct inode *inode, struct file *filp) { struct kvmppc_spapr_tce_table *stt = filp->private_data; struct kvmppc_spapr_tce_iommu_table *stit, *tmp; + struct kvm *kvm = stt->kvm; + mutex_lock(&kvm->lock); list_del_rcu(&stt->list); + mutex_unlock(&kvm->lock); list_for_each_entry_safe(stit, tmp, &stt->iommu_tables, next) { WARN_ON(!kref_read(&stit->kref)); @@ -298,7 +301,6 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm, unsigned long npages, size; int ret = -ENOMEM; int i; - int fd = -1; if (!args->size) return -EINVAL; @@ -328,11 +330,6 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm, goto fail; } - ret = fd = anon_inode_getfd("kvm-spapr-tce", &kvm_spapr_tce_fops, - stt, O_RDWR | O_CLOEXEC); - if (ret < 0) - goto fail; - mutex_lock(&kvm->lock); /* Check this LIOBN hasn't been previously allocated */ @@ -344,17 +341,19 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm, } } - if (!ret) { + if (!ret) + ret = anon_inode_getfd("kvm-spapr-tce", &kvm_spapr_tce_fops, + stt, O_RDWR | O_CLOEXEC); + + if (ret >= 0) { list_add_rcu(&stt->list, &kvm->arch.spapr_tce_tables); kvm_get_kvm(kvm); } mutex_unlock(&kvm->lock); - if (!ret) - return fd; - - put_unused_fd(fd); + if (ret >= 0) + return ret; fail: for (i = 0; i < npages; i++)