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=BAYES_00, 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 CDDEAC4363A for ; Mon, 5 Oct 2020 17:21:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9261D20665 for ; Mon, 5 Oct 2020 17:21:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727033AbgJERVx (ORCPT ); Mon, 5 Oct 2020 13:21:53 -0400 Received: from mga07.intel.com ([134.134.136.100]:44121 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725973AbgJERVx (ORCPT ); Mon, 5 Oct 2020 13:21:53 -0400 IronPort-SDR: KTVOLNrkJ01X0YSHcBJ6MuwH6TG/5R1Z+DHAiZmo/b/RQ7jkAmifpNt9RRstW9aQmJlCwxIbrM OBpm3N9ibVpA== X-IronPort-AV: E=McAfee;i="6000,8403,9765"; a="227922863" X-IronPort-AV: E=Sophos;i="5.77,340,1596524400"; d="scan'208";a="227922863" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga105.jf.intel.com with ESMTP; 05 Oct 2020 10:21:41 -0700 IronPort-SDR: 9KZPT6jybuDXjyx2wdoy5gF6v83jpIj18GzyYnrTPhFpIiekhoAt0/+56OUkqBiA3/mLMZLVvm WeMviodU9m0w== X-IronPort-AV: E=Sophos;i="5.77,340,1596524400"; d="scan'208";a="314583091" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.160]) by orsmga006-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Oct 2020 08:55:32 -0700 Date: Mon, 5 Oct 2020 08:55:19 -0700 From: Sean Christopherson To: Jarkko Sakkinen Cc: linux-sgx@vger.kernel.org, Haitao Huang , Matthew Wilcox , Jethro Beekman , Dave Hansen Subject: Re: [PATCH v3] x86/sgx: Fix sgx_encl_may_map locking Message-ID: <20201005155519.GB11938@linux.intel.com> References: <20201005141119.5395-1-jarkko.sakkinen@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201005141119.5395-1-jarkko.sakkinen@linux.intel.com> User-Agent: Mutt/1.5.24 (2015-08-30) Precedence: bulk List-ID: X-Mailing-List: linux-sgx@vger.kernel.org On Mon, Oct 05, 2020 at 05:11:19PM +0300, Jarkko Sakkinen wrote: > @@ -317,11 +319,30 @@ int sgx_encl_may_map(struct sgx_encl *encl, unsigned long start, > if (current->personality & READ_IMPLIES_EXEC) > return -EACCES; > > - xas_for_each(&xas, page, idx_end) > - if (!page || (~page->vm_max_prot_bits & vm_prot_bits)) > - return -EACCES; > + /* > + * No need to hold encl->lock: > + * 1. None of the page->* get written. > + * 2. page->vm_max_prot_bits is set in sgx_encl_page_alloc(). This > + * is before calling xa_insert(). After that it is never modified. > + */ You forgot to cover racing with insertion, e.g. below is the snippet from my original patch[*], which did the lookup without protection from encl->lock.` + /* + * No need to take encl->lock, vm_prot_bits is set prior to + * insertion and never changes, and racing with adding pages is + * a userspace bug. + */ + rcu_read_lock(); + page = radix_tree_lookup(&encl->page_tree, idx); + rcu_read_unlock(); [*]https://patchwork.kernel.org/patch/11005431/