From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2E2B6C4167B for ; Tue, 5 Apr 2022 13:37:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1389428AbiDENdw (ORCPT ); Tue, 5 Apr 2022 09:33:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60052 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345993AbiDEJXP (ORCPT ); Tue, 5 Apr 2022 05:23:15 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 292E5A8ED2; Tue, 5 Apr 2022 02:12:45 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 98831B818F3; Tue, 5 Apr 2022 09:12:43 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E1179C385A3; Tue, 5 Apr 2022 09:12:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1649149962; bh=HmXyQy+1K/lealDgdQq2ot7mCjmICWhV+Bgh4pBkcn0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=DKFs3s7VzLXfX61/QrJfyaJsJWdIMNfijBVdnjeGAoiSSh5cztwMEKyGOVaY3d8zZ g0Ddn7ANVmDEQF/Qr/QZtpx0KxsJCiP/4P7m4v8GPZ5O6GsLn3dIZm2gG9083sV4yO QfifREBxznTYinmPkJazEnFrvs6OC/XgXhg+nZxw= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Ben Gardon , David Matlack , Paolo Bonzini Subject: [PATCH 5.16 0904/1017] KVM: Prevent module exit until all VMs are freed Date: Tue, 5 Apr 2022 09:30:17 +0200 Message-Id: <20220405070421.058915912@linuxfoundation.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220405070354.155796697@linuxfoundation.org> References: <20220405070354.155796697@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: David Matlack commit 5f6de5cbebee925a612856fce6f9182bb3eee0db upstream. Tie the lifetime the KVM module to the lifetime of each VM via kvm.users_count. This way anything that grabs a reference to the VM via kvm_get_kvm() cannot accidentally outlive the KVM module. Prior to this commit, the lifetime of the KVM module was tied to the lifetime of /dev/kvm file descriptors, VM file descriptors, and vCPU file descriptors by their respective file_operations "owner" field. This approach is insufficient because references grabbed via kvm_get_kvm() do not prevent closing any of the aforementioned file descriptors. This fixes a long standing theoretical bug in KVM that at least affects async page faults. kvm_setup_async_pf() grabs a reference via kvm_get_kvm(), and drops it in an asynchronous work callback. Nothing prevents the VM file descriptor from being closed and the KVM module from being unloaded before this callback runs. Fixes: af585b921e5d ("KVM: Halt vcpu if page it tries to access is swapped out") Fixes: 3d3aab1b973b ("KVM: set owner of cpu and vm file operations") Cc: stable@vger.kernel.org Suggested-by: Ben Gardon [ Based on a patch from Ben implemented for Google's kernel. ] Signed-off-by: David Matlack Message-Id: <20220303183328.1499189-2-dmatlack@google.com> Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman --- virt/kvm/kvm_main.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -117,6 +117,8 @@ EXPORT_SYMBOL_GPL(kvm_debugfs_dir); static const struct file_operations stat_fops_per_vm; +static struct file_operations kvm_chardev_ops; + static long kvm_vcpu_ioctl(struct file *file, unsigned int ioctl, unsigned long arg); #ifdef CONFIG_KVM_COMPAT @@ -1107,6 +1109,16 @@ static struct kvm *kvm_create_vm(unsigne preempt_notifier_inc(); kvm_init_pm_notifier(kvm); + /* + * When the fd passed to this ioctl() is opened it pins the module, + * but try_module_get() also prevents getting a reference if the module + * is in MODULE_STATE_GOING (e.g. if someone ran "rmmod --wait"). + */ + if (!try_module_get(kvm_chardev_ops.owner)) { + r = -ENODEV; + goto out_err; + } + return kvm; out_err: @@ -1196,6 +1208,7 @@ static void kvm_destroy_vm(struct kvm *k preempt_notifier_dec(); hardware_disable_all(); mmdrop(mm); + module_put(kvm_chardev_ops.owner); } void kvm_get_kvm(struct kvm *kvm)