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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=unavailable 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 44238C43612 for ; Mon, 17 Dec 2018 18:36:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 21CB820675 for ; Mon, 17 Dec 2018 18:36:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389081AbeLQSgO (ORCPT ); Mon, 17 Dec 2018 13:36:14 -0500 Received: from mga06.intel.com ([134.134.136.31]:1438 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387614AbeLQSgO (ORCPT ); Mon, 17 Dec 2018 13:36:14 -0500 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga104.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 17 Dec 2018 10:36:13 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,366,1539673200"; d="scan'208";a="119043409" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.154]) by orsmga002.jf.intel.com with ESMTP; 17 Dec 2018 10:36:13 -0800 Date: Mon, 17 Dec 2018 10:36:13 -0800 From: Sean Christopherson To: Jarkko Sakkinen Cc: Dave Hansen , x86@kernel.org, platform-driver-x86@vger.kernel.org, linux-sgx@vger.kernel.org, nhorman@redhat.com, npmccallum@redhat.com, serge.ayoun@intel.com, shay.katz-zamir@intel.com, haitao.huang@linux.intel.com, andriy.shevchenko@linux.intel.com, tglx@linutronix.de, kai.svahn@intel.com, mark.shanahan@intel.com, luto@amacapital.net, Suresh Siddha , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Darren Hart , Andy Shevchenko , "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" Subject: Re: [PATCH v17 18/23] platform/x86: Intel SGX driver Message-ID: <20181217183613.GD12491@linux.intel.com> References: <20181116010412.23967-1-jarkko.sakkinen@linux.intel.com> <20181116010412.23967-19-jarkko.sakkinen@linux.intel.com> <7d5cde02-4649-546b-0f03-2d6414bb80b5@intel.com> <20181217180102.GA12560@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181217180102.GA12560@linux.intel.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 17, 2018 at 08:01:02PM +0200, Jarkko Sakkinen wrote: > On Mon, Dec 17, 2018 at 09:45:40AM -0800, Dave Hansen wrote: > > > +struct sgx_encl *sgx_encl_alloc(struct sgx_secs *secs) > > > +{ > > ... > > > + kref_init(&encl->refcount); > > > + INIT_LIST_HEAD(&encl->add_page_reqs); > > > + INIT_RADIX_TREE(&encl->page_tree, GFP_KERNEL); > > > + mutex_init(&encl->lock); > > > + INIT_WORK(&encl->add_page_work, sgx_add_page_worker); > > > + > > > + encl->mm = current->mm; <---------------------------------> + encl->base = secs->base; > > > + encl->size = secs->size; > > > + encl->ssaframesize = secs->ssa_frame_size; > > > + encl->backing = backing; > > > + > > > + return encl; > > > +} > > > > How is this OK without taking a reference on the mm? It's subtle and the ordering is all kinds of weird, but technically we are taking a reference on mm when the mmu_notifier is registered in sgx_encl_create(). sgx_encl_alloc() and sgx_encl_create() are always called in tandem and with mm->mm_users > 0, so we'll never use encl->mm without holding a reference to mm. We need to comment the weirdness or maybe register the notifier before > > I have a feeling a bunch of your bugs with the mmu notifiers and so > > forth are because the refcounting is wrong here. Eh, not really. Maybe the mmu_notifier is more subtle, e.g. calling do_unmap() after mmput() would be quite obvious, but there's no fundamental bug, we just haven't needed to touch VMAs during release prior to moving away from shmem. > > Sean's SGX_ENCL_MM_RELEASED would, I think be unnecessary if you just > > take a refcount here and release it when the enclave is destroyed. > > Right, atomic_inc(encl->mm->count) here and once when releasing. > > The we would not even need the whole mmu notifier in the first place. I'm pretty sure doing mmget() would result in circular dependencies and a zombie enclave. In the do_exit() case where a task is abruptly killed: - __mmput() is never called because the enclave holds a ref - sgx_encl_release() is never be called because its VMAs hold refs - sgx_vma_close() is never called because __mmput()->exit_mmap() is blocked and the process itself is dead, i.e. won't unmap anything.