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,NICE_REPLY_A,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 91F9FC433B4 for ; Tue, 18 May 2021 21:48:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 686CE61261 for ; Tue, 18 May 2021 21:48:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352632AbhERVuB (ORCPT ); Tue, 18 May 2021 17:50:01 -0400 Received: from mga14.intel.com ([192.55.52.115]:16912 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236298AbhERVt7 (ORCPT ); Tue, 18 May 2021 17:49:59 -0400 IronPort-SDR: DKyyichX1IUZVXkmPCSN3AWb2JW+eqRxBZC+7ESwn2zw88FoN+dhB7LcmpeCyDRJM5lbOxpB7G NSZWmJTH/0Ow== X-IronPort-AV: E=McAfee;i="6200,9189,9988"; a="200524579" X-IronPort-AV: E=Sophos;i="5.82,310,1613462400"; d="scan'208";a="200524579" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 May 2021 14:48:41 -0700 IronPort-SDR: pLyD72iVxOHTJiAI6YsrUf6P71lNg593hFHGbEUjWmynh4aV30K2s2UmOEhKCyB+vCY9JQqjve 8ouXL7nbAycw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.82,310,1613462400"; d="scan'208";a="439649931" Received: from mattu-haswell.fi.intel.com (HELO [10.237.72.170]) ([10.237.72.170]) by orsmga008.jf.intel.com with ESMTP; 18 May 2021 14:48:38 -0700 Subject: Re: [PATCH v2 1/4] usb: early: Avoid using DbC if already enabled To: Connor Davis , Jan Beulich Cc: Jann Horn , Lee Jones , Chunfeng Yun , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, Greg Kroah-Hartman References: <8ccce25a-e3ca-cb30-f6a3-f9243a85a49b@suse.com> <16400ee4-4406-8b26-10c0-a423b2b1fed0@gmail.com> <55325db1-b086-fc81-9117-6560c4914a12@gmail.com> From: Mathias Nyman Autocrypt: addr=mathias.nyman@linux.intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <55325db1-b086-fc81-9117-6560c4914a12@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17.5.2021 17.24, Connor Davis wrote: > > On 5/17/21 8:13 AM, Jan Beulich wrote: >> On 17.05.2021 15:48, Connor Davis wrote: >>> On 5/17/21 3:32 AM, Jan Beulich wrote: >>>> On 14.05.2021 02:56, Connor Davis wrote: >>>>> Check if the debug capability is enabled in early_xdbc_parse_parameter, >>>>> and if it is, return with an error. This avoids collisions with whatever >>>>> enabled the DbC prior to linux starting. >>>> Doesn't this go too far and prevent use even if firmware (perhaps >>>> mistakenly) left it enabled? >>> Yes, but how is one supposed to distinguish the broken firmware and >>> non-broken >>> >>> firmware cases? >> Well, a first step might be to only check if running virtualized. >> And then if your running virtualized, there might be a way to >> inquire the hypervisor? > > Right, but if it was enabled by something other than a hypervisor, > > or you're not running virtualized, how do you distinguish then? IMO > > the proper thing to do in any case is to simply not use the DbC in linux. > Sounds reasonable. We can address "broken firmware" during the xHC handoff from BIOS to OS. Only first OS that loads after BIOS should see the "HC BIOS owned semaphore" bit set in xHCI MMIO. If it's set then OS requests ownership, which clears BIOS owned bit. If DbC is running here we can stop it. -Mathias