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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 B81FCC3A5A3 for ; Tue, 27 Aug 2019 12:11:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8F6C9206BF for ; Tue, 27 Aug 2019 12:11:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726539AbfH0MLe (ORCPT ); Tue, 27 Aug 2019 08:11:34 -0400 Received: from mga14.intel.com ([192.55.52.115]:50321 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726190AbfH0MLe (ORCPT ); Tue, 27 Aug 2019 08:11:34 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by fmsmga103.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 27 Aug 2019 05:11:28 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,437,1559545200"; d="scan'208";a="380893339" Received: from jsakkine-mobl1.fi.intel.com (HELO localhost) ([10.237.66.169]) by fmsmga006.fm.intel.com with ESMTP; 27 Aug 2019 05:11:26 -0700 Date: Tue, 27 Aug 2019 15:11:25 +0300 From: Jarkko Sakkinen To: Sean Christopherson Cc: linux-sgx@vger.kernel.org Subject: Re: [PATCH 3/4] x86/sgx: Reject concurrent ioctls on single enclave Message-ID: <20190827121125.rmcsf2qlicb4xduf@linux.intel.com> References: <20190827001128.25066-1-sean.j.christopherson@intel.com> <20190827001128.25066-4-sean.j.christopherson@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190827001128.25066-4-sean.j.christopherson@intel.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo User-Agent: NeoMutt/20180716 Sender: linux-sgx-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-sgx@vger.kernel.org On Mon, Aug 26, 2019 at 05:11:27PM -0700, Sean Christopherson wrote: > Except for ENCLAVE_SET_ATTRIBUTE, all SGX ioctls() must be executed > serially to successfully initialize an enclave, e.g. the kernel already > strictly requires ECREATE->EADD->EINIT, and concurrent EADDs will result > in an unstable MRENCLAVE. Explicitly enforce serialization by returning > EINVAL if userspace attempts an ioctl while a different ioctl for the > same enclave is in progress. > > The primary beneficiary of explicit serialization is sgx_encl_grow() as > it no longer has to deal with dropping and reacquiring encl->lock when > a new VA page needs to be allocated. Eliminating the lock juggling in > sgx_encl_grow() paves the way for fixing a lock ordering bug in > ENCLAVE_ADD_PAGE without having to also juggle mm->mmap_sem. > > Serializing ioctls also fixes a race between ENCLAVE_CREATE and > ENCLAVE_SET_ATTRIBUTE, as the latter does not take encl->lock, e.g. > concurrent updates to allowed_attributes could result in a stale > value. The race could also be fixed by taking encl->lock, but that > is less desirable as doing so would unnecessarily interfere with EPC >b page reclaim. > > Signed-off-by: Sean Christopherson I think the error code should be -EBUSY. Our implementation is fairly coherent at the moment that -EINVAL follows from bad input data. Getting -EINVAL from this would be a bit confusing. If atomic_t was used for the enclave flags (see my comment to 1/4), then I think we could implement this like: if (atomic_fetch_or(SGX_ENCL_IOCTL, &encl->flags) & SGX_ENCL_IOCTL) return -EIOCTL; /Jarkko