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_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 DC81FC433E0 for ; Mon, 29 Jun 2020 18:59:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C4921204EC for ; Mon, 29 Jun 2020 18:59:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730270AbgF2S7U (ORCPT ); Mon, 29 Jun 2020 14:59:20 -0400 Received: from mga09.intel.com ([134.134.136.24]:65096 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730167AbgF2S6y (ORCPT ); Mon, 29 Jun 2020 14:58:54 -0400 IronPort-SDR: RWeeJ/8RlA8iam6h8rbkXQySlJPKg8Z8etXIA2PTHkj4OQbn5OXZrrwy1WPNeaYMZIpLnY12r3 SoN2lGVZg+wg== X-IronPort-AV: E=McAfee;i="6000,8403,9666"; a="147540174" X-IronPort-AV: E=Sophos;i="5.75,295,1589266800"; d="scan'208";a="147540174" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Jun 2020 08:27:19 -0700 IronPort-SDR: rGBMpfACiG1z4qkmaDQmtluftmaItl/SFgyVE8IlcTxjEYsTQkMzUpPHkLlLoyg+bUyRjEZRro RXKZLVmhfq9w== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.75,295,1589266800"; d="scan'208";a="318245592" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.152]) by orsmga007.jf.intel.com with ESMTP; 29 Jun 2020 08:27:19 -0700 Date: Mon, 29 Jun 2020 08:27:19 -0700 From: Sean Christopherson To: Borislav Petkov Cc: Jarkko Sakkinen , x86@kernel.org, linux-sgx@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, Jethro Beekman , Haitao Huang , Chunyang Hui , Jordan Hand , Nathaniel McCallum , Seth Moore , Suresh Siddha , akpm@linux-foundation.org, andriy.shevchenko@linux.intel.com, asapek@google.com, cedric.xing@intel.com, chenalexchen@google.com, conradparker@google.com, cyhanish@google.com, dave.hansen@intel.com, haitao.huang@intel.com, josh@joshtriplett.org, kai.huang@intel.com, kai.svahn@intel.com, kmoy@google.com, ludloff@google.com, luto@kernel.org, nhorman@redhat.com, puiterwijk@redhat.com, rientjes@google.com, tglx@linutronix.de, yaozhangx@google.com Subject: Re: [PATCH v33 11/21] x86/sgx: Linux Enclave Driver Message-ID: <20200629152718.GA12312@linux.intel.com> References: <20200617220844.57423-1-jarkko.sakkinen@linux.intel.com> <20200617220844.57423-12-jarkko.sakkinen@linux.intel.com> <20200627174335.GC15585@zn.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200627174335.GC15585@zn.tnic> 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 Sat, Jun 27, 2020 at 07:43:35PM +0200, Borislav Petkov wrote: > On Thu, Jun 18, 2020 at 01:08:33AM +0300, Jarkko Sakkinen wrote: > > +static int sgx_encl_init(struct sgx_encl *encl, struct sgx_sigstruct *sigstruct, > > + void *token) > > +{ > > + u64 mrsigner[4]; > > + int ret; > > + int i; > > + int j; > > + > > + /* Check that the required attributes have been authorized. */ > > + if (encl->secs_attributes & ~encl->allowed_attributes) > > + return -EACCES; > > + > > + ret = sgx_get_key_hash(sigstruct->modulus, mrsigner); > > + if (ret) > > + return ret; > > + > > + mutex_lock(&encl->lock); > > + > > + if (atomic_read(&encl->flags) & SGX_ENCL_INITIALIZED) { > > + ret = -EFAULT; > > + goto err_out; > > + } > > That test should be the first thing this function or its caller does. Hmm, I was going to say that SGX_ENCL_INITIALIZED can't be checked until encl->lock is held, but that's not true for this path as mutual exclusion is provided by the SGX_ENCL_IOCTL flag. So yeah, this can be checked at the same time as SGX_ENCL_CREATED in sgx_ioc_enclave_init(). > > + for (i = 0; i < SGX_EINIT_SLEEP_COUNT; i++) { > > + for (j = 0; j < SGX_EINIT_SPIN_COUNT; j++) { > > Ew, what's that double-loop for? > > It tries to init an enclave a bunch of times. Why does it need to init > more than once? ENCLS[EINIT] is interruptible because it has such a high latency, e.g. 50k+ cycles on success. If an IRQ/NMI/SMI becomes pending, EINIT may fail with SGX_UNMASKED_EVENT so that the event can be serviced. The idea behind the double loop is to try EINIT in a tight loop, then back off and sleep for a while before retrying that tight inner loop. > > + ret = sgx_einit(sigstruct, token, encl->secs.epc_page, > > + mrsigner); > > + if (ret == SGX_UNMASKED_EVENT) > > + continue; > > + else > > + break; > > + } > > + > > + if (ret != SGX_UNMASKED_EVENT) > > + break; > > + > > + msleep_interruptible(SGX_EINIT_SLEEP_TIME); > > + > > + if (signal_pending(current)) { > > + ret = -ERESTARTSYS; > > + goto err_out; > > + } > > + } > > + > > + if (ret & ENCLS_FAULT_FLAG) { > > + if (encls_failed(ret)) > > + ENCLS_WARN(ret, "EINIT"); > > + > > + sgx_encl_destroy(encl); > > + ret = -EFAULT; > > + } else if (ret) { > > + pr_debug("EINIT returned %d\n", ret); > > + ret = -EPERM; > > + } else { > > + atomic_or(SGX_ENCL_INITIALIZED, &encl->flags); > > + } > > + > > +err_out: > > + mutex_unlock(&encl->lock); > > + return ret; > > +} > > + > > +/** > > + * sgx_ioc_enclave_init - handler for %SGX_IOC_ENCLAVE_INIT > > + * > > + * @filep: open file to /dev/sgx > > @encl: pointer to an enclave instance (via ioctl() file pointer) > > > + * @arg: userspace pointer to a struct sgx_enclave_init instance > > + * > > + * Flush any outstanding enqueued EADD operations and perform EINIT. The > > + * Launch Enclave Public Key Hash MSRs are rewritten as necessary to match > > + * the enclave's MRSIGNER, which is caculated from the provided sigstruct. > > + * > > + * Return: > > + * 0 on success, > > + * SGX error code on EINIT failure, > > + * -errno otherwise > > + */ > > +static long sgx_ioc_enclave_init(struct sgx_encl *encl, void __user *arg) > > +{ > > + struct sgx_sigstruct *sigstruct; > > + struct sgx_enclave_init einit; > > + struct page *initp_page; > > + void *token; > > + int ret; > > + > > + if (!(atomic_read(&encl->flags) & SGX_ENCL_CREATED)) > > Might just as well check the other flags: doing EINIT on an already > initialized enclave - SGX_ENCL_INITIALIZED - is perhaps a nono or > similarly on a SGX_ENCL_DEAD enclave. > > And you could do similar sanity checks in the other ioctl functions. Ya, as above, SGX_ENCL_INITIALIZED can be checked here. SGX_ENCL_DEAD is actually already checked in in the top level sgx_ioctl(), i.e. the check in sgx_encl_add_page() can technically be flat out dropped. I say "technically" because I'm a bit torn over SGX_ENCL_DEAD; encl->lock must be held to SGX_ENCL_DEAD (the page fault and reclaim flows rely on this), but as it stands today only ioctl() paths (guarded by SGX_ENCL_IOCTL) and sgx_release() (makes the ioctls() unreachable) set SGX_ENCL_DEAD. So it's safe to check SGX_ENCL_DEAD from ioctl() context without holding encl->lock, at least in the current code base, but it feels weird/sketchy. In the end I don't think I have a strong opinion. Removing the technically unnecessary DEAD check in sgx_encl_add_page() is the simplest change, so it may make sense to do that and nothing more for initial upstreaming. Long term, I fully expect we'll add paths that set SGX_ENCL_DEAD outside of ioctl() context, e.g. to handle EPC OOM, but it wouldn't be a bad thing to have a standalone commit in a future series to add DEAD checks (under encl->lock) in the ADD and INIT flows.