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 X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1AAA3C43331 for ; Fri, 3 Apr 2020 23:42:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E2207206F8 for ; Fri, 3 Apr 2020 23:42:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725980AbgDCXmk (ORCPT ); Fri, 3 Apr 2020 19:42:40 -0400 Received: from mga01.intel.com ([192.55.52.88]:12779 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725268AbgDCXmk (ORCPT ); Fri, 3 Apr 2020 19:42:40 -0400 IronPort-SDR: h9BXXORRZSxzidewDZvhtG1fZF/KvP2zG2ypVIEJi/VhHwNpzaIFrxT7tQRDPu61957hZcSQjr GiFhCPWVndzg== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Apr 2020 16:42:40 -0700 IronPort-SDR: 0ZpsFunNm2zSVx7PPqZYIEbwSfViqQJMlkjxSNurr4OQSFXlGYJOR3qqcht1YZxCtQPUwdXGNr xcyOSHgC+New== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,341,1580803200"; d="scan'208";a="253527807" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by orsmga006.jf.intel.com with ESMTP; 03 Apr 2020 16:42:39 -0700 Date: Fri, 3 Apr 2020 16:42:39 -0700 From: Sean Christopherson To: Jarkko Sakkinen Cc: linux-sgx@vger.kernel.org, Haitao Huang Subject: Re: [PATCH v2] x86/sgx: Fix deadlock and race conditions between fork() and EPC reclaim Message-ID: <20200403234239.GJ2701@linux.intel.com> References: <20200403093550.104789-1-jarkko.sakkinen@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200403093550.104789-1-jarkko.sakkinen@linux.intel.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-sgx-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-sgx@vger.kernel.org On Fri, Apr 03, 2020 at 12:35:50PM +0300, Jarkko Sakkinen wrote: > From: Sean Christopherson > @@ -221,12 +224,16 @@ int sgx_encl_mm_add(struct sgx_encl *encl, struct mm_struct *mm) > return ret; > } > > + /* > + * The page reclaimer uses list version for synchronization instead of > + * synchronize_scru() because otherwise we could conflict with > + * dup_mmap(). > + */ > spin_lock(&encl->mm_lock); > list_add_rcu(&encl_mm->list, &encl->mm_list); You dropped the smp_wmb(). > + encl->mm_list_version++; > spin_unlock(&encl->mm_lock); > > - synchronize_srcu(&encl->srcu); > - > return 0; > } > > diff --git a/arch/x86/kernel/cpu/sgx/encl.h b/arch/x86/kernel/cpu/sgx/encl.h > index 44b353aa8866..f0f72e591244 100644 > --- a/arch/x86/kernel/cpu/sgx/encl.h > +++ b/arch/x86/kernel/cpu/sgx/encl.h > @@ -74,6 +74,7 @@ struct sgx_encl { > struct mutex lock; > struct list_head mm_list; > spinlock_t mm_lock; > + unsigned long mm_list_version; > struct file *backing; > struct kref refcount; > struct srcu_struct srcu; > diff --git a/arch/x86/kernel/cpu/sgx/reclaim.c b/arch/x86/kernel/cpu/sgx/reclaim.c > index 39f0ddefbb79..5fb8bdfa6a1f 100644 > --- a/arch/x86/kernel/cpu/sgx/reclaim.c > +++ b/arch/x86/kernel/cpu/sgx/reclaim.c > @@ -184,28 +184,38 @@ static void sgx_reclaimer_block(struct sgx_epc_page *epc_page) > struct sgx_encl_page *page = epc_page->owner; > unsigned long addr = SGX_ENCL_PAGE_ADDR(page); > struct sgx_encl *encl = page->encl; > + unsigned long mm_list_version; > struct sgx_encl_mm *encl_mm; > struct vm_area_struct *vma; > int idx, ret; > > - idx = srcu_read_lock(&encl->srcu); > + do { > + mm_list_version = encl->mm_list_version; > > - list_for_each_entry_rcu(encl_mm, &encl->mm_list, list) { > - if (!mmget_not_zero(encl_mm->mm)) > - continue; > + /* Fence reads as the CPU can reorder them. This guarantees > + * that we don't access old list with a new version. This comment is flat out wrong. This has nothing to do the CPU reordering things. The smp_{r,w}mb() are nothing more than compiler barriers, and even those go away when the kernel is built with SMP=0. I don't mind gutting the other comments, but there is a well established pattern form smb_wmb()/smp_rmb() pairs, I would strongly prefer to keep the exact comment I submitted. > + */ > + smp_rmb(); > > - down_read(&encl_mm->mm->mmap_sem); > + idx = srcu_read_lock(&encl->srcu); > > - ret = sgx_encl_find(encl_mm->mm, addr, &vma); > - if (!ret && encl == vma->vm_private_data) > - zap_vma_ptes(vma, addr, PAGE_SIZE); > + list_for_each_entry_rcu(encl_mm, &encl->mm_list, list) { > + if (!mmget_not_zero(encl_mm->mm)) > + continue; > > - up_read(&encl_mm->mm->mmap_sem); > + down_read(&encl_mm->mm->mmap_sem); > > - mmput_async(encl_mm->mm); > - } > + ret = sgx_encl_find(encl_mm->mm, addr, &vma); > + if (!ret && encl == vma->vm_private_data) > + zap_vma_ptes(vma, addr, PAGE_SIZE); > > - srcu_read_unlock(&encl->srcu, idx); > + up_read(&encl_mm->mm->mmap_sem); > + > + mmput_async(encl_mm->mm); > + } > + > + srcu_read_unlock(&encl->srcu, idx); > + } while (unlikely(encl->mm_list_version != mm_list_version)); > > mutex_lock(&encl->lock); > > @@ -250,6 +260,11 @@ static const cpumask_t *sgx_encl_ewb_cpumask(struct sgx_encl *encl) > struct sgx_encl_mm *encl_mm; > int idx; > > + /* > + * Can race with sgx_encl_mm_add(), but ETRACK has already been > + * executed, which means that the CPUs running in the new mm will enter > + * into the enclave with a fresh epoch. > + */ > cpumask_clear(cpumask); > > idx = srcu_read_lock(&encl->srcu); > -- > 2.25.1 >