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=-3.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 C165FC433E6 for ; Mon, 1 Feb 2021 19:02:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7C66C64DDF for ; Mon, 1 Feb 2021 19:02:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229692AbhBATCC (ORCPT ); Mon, 1 Feb 2021 14:02:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59180 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229959AbhBATBz (ORCPT ); Mon, 1 Feb 2021 14:01:55 -0500 Received: from mail-ed1-x52e.google.com (mail-ed1-x52e.google.com [IPv6:2a00:1450:4864:20::52e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0C1BEC061756 for ; Mon, 1 Feb 2021 11:01:15 -0800 (PST) Received: by mail-ed1-x52e.google.com with SMTP id y8so5003423ede.6 for ; Mon, 01 Feb 2021 11:01:14 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=C4j8R2NWjOWWuVLjBbyJdPlrlZ/j8TvzFIyUEA+Ndu8=; b=nyzwIexSmOjDJ+JcSNBcdEk6/yXwTc3YKKDydwVmgfPbkLgTinbZm6+ykK0VQzEtXd 2FGnsXVks/jQjS4fLAnBKnK11OSqp97qHKPP7ZUqdq9zaUFinHt8zs2HO+5Snar6F84v 5kZW9qoTEN+59FePDotW3jAP0kx+s2AOE3I3aKrRS257mRb/6+u9GsKidEMKfGro142s DWpsafh0uFz0iMyedBmo8mVT7/beWRMM3ciL+gitIiUzkwCc6LH/5iwE8X/spV3q0Kbs nPUT/vZZ8B2SFP534Z/VBodBdcFAo7cIr+SWbdYD0ZsBKkAsg8VJmh6BVUYFFwT3Dh2D +6LA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=C4j8R2NWjOWWuVLjBbyJdPlrlZ/j8TvzFIyUEA+Ndu8=; b=atlezGblRG0wa5RuDoQ6gSxwl5Wb8ex20tBzvbHpOibRx3WmqDzkr0qyzj8qnuFuII FftCBaDofALZR6BcMKLdTtjsjVOKXK8mPkYa1BkliC3G1yczg1N1HTwf33UZMa4nW7pH auzAXvCc3Uu3Fh1MgPvpKknq7tLvvimG6Q902VUnSj21dPCUNqVNT/Tyms4riPWHLsna YcdtYn1DvKslxJzDPHzFgMd84WNfponMbnxr0tVM4k7VAqs/qvl1PTfDHPN8hUSqHjCi yOILw2yDyV/72AkEYU9OLobbHggK5W2uLM448HMLd5zptjlVYss4ic04HY/RQkPtCDol Fz7Q== X-Gm-Message-State: AOAM532ZSybCmhNtn7Jt95dxGfvEbTeH/3odypeF0o7ZKC9SUJYXCuFX DFuAyE+OtSj80kGho+Q38b52OxlvCJqIywtWYS8VDQ== X-Google-Smtp-Source: ABdhPJynM6kBjwVDj3TQA0+jvvwTHEb3P0qRRcbLVYHUWU+FzxYi6yyx9m7bmpMHOcX1OWvc84NajYIYsO/BTj6o3/4= X-Received: by 2002:aa7:cd87:: with SMTP id x7mr21185852edv.210.1612206073657; Mon, 01 Feb 2021 11:01:13 -0800 (PST) MIME-Version: 1.0 References: <20210130002438.1872527-1-ben.widawsky@intel.com> <20210130002438.1872527-9-ben.widawsky@intel.com> <20210201181845.GJ197521@fedora> <20210201183455.3dndfwyswwvs2dlm@intel.com> In-Reply-To: <20210201183455.3dndfwyswwvs2dlm@intel.com> From: Dan Williams Date: Mon, 1 Feb 2021 11:01:11 -0800 Message-ID: Subject: Re: [PATCH 08/14] taint: add taint for direct hardware access To: Ben Widawsky Cc: Konrad Rzeszutek Wilk , linux-cxl@vger.kernel.org, Linux ACPI , Linux Kernel Mailing List , linux-nvdimm , Linux PCI , Bjorn Helgaas , Chris Browy , Christoph Hellwig , Ira Weiny , Jon Masters , Jonathan Cameron , Rafael Wysocki , Randy Dunlap , Vishal Verma , daniel.lll@alibaba-inc.com, "John Groves (jgroves)" , "Kelley, Sean V" Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org On Mon, Feb 1, 2021 at 10:35 AM Ben Widawsky wrote: > > On 21-02-01 13:18:45, Konrad Rzeszutek Wilk wrote: > > On Fri, Jan 29, 2021 at 04:24:32PM -0800, Ben Widawsky wrote: > > > For drivers that moderate access to the underlying hardware it is > > > sometimes desirable to allow userspace to bypass restrictions. Once > > > userspace has done this, the driver can no longer guarantee the sanctity > > > of either the OS or the hardware. When in this state, it is helpful for > > > kernel developers to be made aware (via this taint flag) of this fact > > > for subsequent bug reports. > > > > > > Example usage: > > > - Hardware xyzzy accepts 2 commands, waldo and fred. > > > - The xyzzy driver provides an interface for using waldo, but not fred. > > > - quux is convinced they really need the fred command. > > > - xyzzy driver allows quux to frob hardware to initiate fred. > > > > Would it not be easier to _not_ frob the hardware for fred-operation? > > Aka not implement it or just disallow in the first place? > > Yeah. So the idea is you either are in a transient phase of the command and some > future kernel will have real support for fred - or a vendor is being short > sighted and not adding support for fred. > > > > > > > > - kernel gets tainted. > > > - turns out fred command is borked, and scribbles over memory. > > > - developers laugh while closing quux's subsequent bug report. > > > > Yeah good luck with that theory in-the-field. The customer won't > > care about this and will demand a solution for doing fred-operation. > > > > Just easier to not do fred-operation in the first place,no? > > The short answer is, in an ideal world you are correct. See nvdimm as an example > of the real world. > > The longer answer. Unless we want to wait until we have all the hardware we're > ever going to see, it's impossible to have a fully baked, and validated > interface. The RAW interface is my admission that I make no guarantees about > being able to provide the perfect interface and giving the power back to the > hardware vendors and their driver writers. > > As an example, suppose a vendor shipped a device with their special vendor > opcode. They can enable their customers to use that opcode on any driver > version. That seems pretty powerful and worthwhile to me. > Powerful, frightening, and questionably worthwhile when there are already examples of commands that need extra coordination for whatever reason. However, I still think the decision tilts towards allowing this given ongoing spec work. NVDIMM ended up allowing unfettered vendor passthrough given the lack of an organizing body to unify vendors. CXL on the other hand appears to have more gravity to keep vendors honest. A WARN splat with a taint, and a debugfs knob for the truly problematic commands seems sufficient protection of system integrity while still following the Linux ethos of giving system owners enough rope to make their own decisions. > Or a more realistic example, we ship a driver that adds a command which is > totally broken. Customers can utilize the RAW interface until it gets fixed in a > subsequent release which might be quite a ways out. > > I'll say the RAW interface isn't an encouraged usage, but it's one that I expect > to be needed, and if it's not we can always try to kill it later. If nobody is > actually using it, nobody will complain, right :D It might be worthwhile to make RAW support a compile time decision so that Linux distros can only ship support for the commands the CXL driver-dev community has blessed, but I'll leave it to a distro developer to second that approach.