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=-0.8 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS 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 798CDC43381 for ; Mon, 25 Feb 2019 20:20:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3E9F320842 for ; Mon, 25 Feb 2019 20:20:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=hansenpartnership.com header.i=@hansenpartnership.com header.b="ESFgQZXg" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727252AbfBYUUp (ORCPT ); Mon, 25 Feb 2019 15:20:45 -0500 Received: from bedivere.hansenpartnership.com ([66.63.167.143]:56156 "EHLO bedivere.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727021AbfBYUUp (ORCPT ); Mon, 25 Feb 2019 15:20:45 -0500 Received: from localhost (localhost [127.0.0.1]) by bedivere.hansenpartnership.com (Postfix) with ESMTP id C68298EE1A0; Mon, 25 Feb 2019 12:20:44 -0800 (PST) Received: from bedivere.hansenpartnership.com ([127.0.0.1]) by localhost (bedivere.hansenpartnership.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 1TARmK-ay5b0; Mon, 25 Feb 2019 12:20:44 -0800 (PST) Received: from [153.66.254.194] (unknown [50.35.68.20]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by bedivere.hansenpartnership.com (Postfix) with ESMTPSA id 0C9208EE101; Mon, 25 Feb 2019 12:20:44 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=hansenpartnership.com; s=20151216; t=1551126044; bh=EKaNkS1QA1DBSNb0pls3mf5BO2f4cAwPmDQhJIQEtzw=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=ESFgQZXgIRdrEOSQq2x4YsCSzekZIdA/FW9wNqbpeFWVFFJq7L0HtqDMFrE4H7hr/ bDn385rzQrv2OneLbkp3akys/8NneOdFf1fr7IiVEe7EXhxA1eypMSDpsNqkFxfraM wN8m4IpCAgMjBZwpDORRkpKwjISsdMFHJ94Zujq0= Message-ID: <1551126043.3226.45.camel@HansenPartnership.com> Subject: Re: [PATCH] tpm: Add driver for TPM over virtio From: James Bottomley To: Matthew Garrett Cc: David Tolnay , Peter Huewe , Jarkko Sakkinen , Jason Gunthorpe , linux-integrity , "Michael S. Tsirkin" , Jason Wang , virtualization@lists.linux-foundation.org, dgreid@chromium.org, apronin@chromium.org Date: Mon, 25 Feb 2019 12:20:43 -0800 In-Reply-To: References: <388c5b80-21a7-1e91-a11f-3a1c1432368b@gmail.com> <1550849416.2787.5.camel@HansenPartnership.com> <1550873900.2787.25.camel@HansenPartnership.com> <1550885645.3577.31.camel@HansenPartnership.com> <1551025819.3106.25.camel@HansenPartnership.com> <1551108969.3226.26.camel@HansenPartnership.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.26.6 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org On Mon, 2019-02-25 at 11:17 -0800, Matthew Garrett wrote: > On Mon, Feb 25, 2019 at 7:36 AM James Bottomley > wrote: > > > The virtio driver performs discovery via virtio, which crosvm > > > implements already for all of its supported devices. This > > > substantially reduces the amount of TPM-specific code compared to > > > your suggestions, and lowers the barrier to entry for > > > implementing TPM support in other hypervisors which I hope we > > > agree is beneficial. > > > > Well, that's somewhat misleading: The reason we already have two > > hypervisor specific drivers already is because every hypervisor has > > a different virtual discovery mechanism. You didn't find the other > > two hypervisor drivers remotely useful, so why would another > > hypervisor find yours useful? > > The existing hypervisor drivers expose hypervisor-specific details. > This proposed driver provides an abstract interface that is usable by > other hypervisors. It allows building a VM that exposes TPM > functionality without requiring additional hardware emulation, > reducing the hypervisor attack surface. Well, that depends whether you think a virtio bus is an abstract concept or a hypervisor specific detail. There are currently four major hypervisors: xen, kvm, hyper-v and ESX. Of those, only one implements virtio: kvm. I agree virtio is a standard and certainly a slew of minor hypervisors implement it because they need paravirt support on Linux so they piggyback off kvm, but I don't see any of the other major hypervisors jumping on the bandwagon. I certainly agree our lives would be easier if all the major hypervisor vendors would just agree a single paravirt driver standard. > > > For me as a hypervisor implementer, what advantages do you see > > > that would make me decide to implement TPM-specific virtual > > > hardware emulation in the form of TIS rather than simply > > > leveraging a virtio driver like for other virtual devices? > > > > So your argument is that for every device we have in the Linux > > kernel, we should have the N hypervisor paravirt variants for the > > same thing? I assure you that's not going to fly because paravirt > > drivers would then outnumber real drivers by an order of magnitude. > > Well, no - in general there's no need to have more than one virtio > driver for any /class/ of hardware. For various unfortunate accidents > of history we've ended up with multiple cases where we have > hypervisor-specific drivers. Fully agree, that's why I'm doing so now. > Using the more generic virtio > infrastructure reduces the need for that, since any hypervisor should > be able to implement the backend (eg, in this case it'd be very easy > to add support for this driver to qemu, I certainly agree there ... is there a plan for this? > which would allow the use of TPMs without needing to enable a whole > bunch of additional qemu features). This isn't a discussion we'd be > having if we'd pushed back more strongly against hypervisor-specific > solutions in the past. I'm still looking for the pragmatic use case. I think yours is attack surface reduction, because the virtio discovery and operation is less code and therefore more secure than physical hardware discovery and operation? I'm not entirely sure I buy that because the TPM communication interface is pretty simple and it's fairly deep down in the kernel internal stack making it difficult to exploit. James