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=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 65E8EC468C6 for ; Thu, 19 Jul 2018 19:05:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 21C5920684 for ; Thu, 19 Jul 2018 19:05:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 21C5920684 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733174AbeGSTtc (ORCPT ); Thu, 19 Jul 2018 15:49:32 -0400 Received: from mga01.intel.com ([192.55.52.88]:17191 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727401AbeGSTtc (ORCPT ); Thu, 19 Jul 2018 15:49:32 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga101.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 19 Jul 2018 12:05:03 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.51,375,1526367600"; d="scan'208";a="74199434" Received: from tstruk-mobl1.jf.intel.com ([10.7.196.153]) by orsmga001.jf.intel.com with ESMTP; 19 Jul 2018 12:05:03 -0700 Subject: Re: [PATCH] tpm: add support for partial reads To: James Bottomley , jarkko.sakkinen@linux.intel.com Cc: jgg@ziepe.ca, linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org References: <153201555276.20155.1352499992826895966.stgit@tstruk-mobl1.jf.intel.com> <1532020750.5396.4.camel@HansenPartnership.com> <421c4b75-9e9d-7045-adad-797fd112898a@intel.com> <1532026030.3198.2.camel@HansenPartnership.com> From: Tadeusz Struk Openpgp: preference=signencrypt Autocrypt: addr=tadeusz.struk@intel.com; prefer-encrypt=mutual; keydata= xsDiBEiLICMRBADteQacQxypsuFvAw6IwYzbD8pgQi+kLYBcqfGgVAUN/cO+sLl6u1lVdaDB fhAArdbV9lpoqcWnmhQFTb4A+W569EpydBr6nuatWkEB+fmmx8YoUtuZfXt7v+1l1rc09kaW LY+TkwQkvFCeuvdasgmBLnmRWymEGWi1E12hUgTw/wCgtK24geC7XkiuANMv0gpr+raOgQMD /2yJZ0SeXQApWyTRaeIYN8GgYHZTWuBp/ofN+viEkhrDxahcaGPP5B/Nv6VS1+M0e5m8OzHj qPUbgfyOeJcslC5aoZdqqqzVWVLaA/+Jy+O+6T3k3R/IryVVATldBlwnGFDhET0mKQsd15zt cIdQBBbfSFR5VlugZuWV5q442IpPA/4g7nen9FFPxh45Te8D54hAsOCywjm6xUE0UJGYHeJ/ MXCPtuXfVCbYcOxZVH7kUS2Vtk5d3bF40IE2WnVq1ZScNANF4ZjikxYhYGfNWX3HXak1gSoj UrY87rMSjPIAry4L0BoIx2qgL/k4iV/3QcXL4t5wosU0iw++suf1zGGcKM0gVGFkZXVzeiBT dHJ1ayA8dHN0cnVrQGdtYWlsLmNvbT7CYwQTEQIAIwIbAwYLCQgHAwIEFQIIAwQWAgMBAh4B AheABQJQTjJTAhkBAAoJEDFswfskq9xyqvcAoI2nsaUCX8ZGbu+Jhq+++qlBFJ2rAJ983RoO R2ofHhn3g3Qi4K34tw0l087BTQRauzUlARAAqkWRL/InEPnoGMg/gw/CRaDBaIBgMsvIcghI 7xevIzpleXt6jKHghSBooH+zaT7qi4u2gkgPn4odsER3Rm94XgrZJgoqls6EpKMWpJNGP4HT eYgykhfsZOLX8ijUbjTM/Sm/dZVo6aYoBL2+ciJwyl+Zt3Mp6un3/GWu6cA9005V50pRqO7j PTlVCHi2bedcEEf5DDsYJv/3Oz8/4LpSf6BL6BltjeZVa2y03dTMmD031JTH+OuyJm1yh72Z HWxhlYNXOv6uFJJVr+paQjrAsBVIYKhK24bD+uGJxLm8AN9i7/Si+2YeSsXvKUhk9mIoFBnU VFo63cziRTcpRu/kXgDAbujwN88qytEcvhEZHS6B9vdws+lhTpolEjkLCkz0Y59z4Fs9srKy QkRN+wtdiLgrwyDW3ryAKxcDmOumGWebDxpaOI/pBhrlS93HmDlvj7JmgTUU4a/NhwI3dXh5 pn8FZzZyVXe3Kc3bu5T3UAC7uztinsAvCJQS6jGZWrXmXkqYkaLXQOw61eInWjr01zE/zDbE mdJPM0+va/gtZx9TtGxr4PpjbqswqCiubLDZXZHh5uqArPv/i+E8aXIsNSTN6Rrqs1j9YgDN ALksibv6+tXH3sOlCUgjuZgJH3+s/mnaAtiV2rZ/WlH15d6nd0uiDSZrKhlR+g4NHMh1ztEA EQEAAcJPBBgRAgAPBQJauzUlAhsMBQkJZgGAAAoJEDFswfskq9xyfv8AoI8aPrJCoM0h5WOP kKxMmPEPHzUNAJ9jBBYXhX1CWg+IhI7i/fLlI0vwCA== Message-ID: Date: Thu, 19 Jul 2018 12:05:02 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <1532026030.3198.2.camel@HansenPartnership.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/19/2018 11:47 AM, James Bottomley wrote: > On Thu, 2018-07-19 at 10:54 -0700, Tadeusz Struk wrote: >> On 07/19/2018 10:19 AM, James Bottomley wrote: >>> That's just an implementation, though, what's the use case? >> >> Hi James, >> The use case is described in the TCTI spec [1] in the >> "3.2.5.2 receive" section. > > Well, yes, but I think we've all agreed that the /dev/tpm and > /dev/tpmrmX aren't TCTI interfaces, although you can layer TCTI on top > of them, so why not simply do fragmentation on top if you need it? > > The reason for not doing it in the interface is that it alters the ABI. > Before this patch we had a hard packet boundary: one packet per read, > one per write and a -EFAULT if you fail to provide a correctly sized > buffer. Now if you provide a buffer too small but don't know about the > fragmentation you're going to misprocess a packet (because you think > you got a whole reply but you didn't) and then you get a -EBUSY on your > next command which you don't know how to handle. The only way out is > to update the applications to handle the new behaviour, which is a no- > no in Linux ABI terms. Don't all the existing applications that read a response in one go do a 4K read now? So nothing will change for them. They will work exactly the same with this change as they do without it. This doesn't break the ABI. > > It might be possible to layer the behaviour you want compatibly into > the current device structure (say an ioctl to switch to the fragment > behaviour) but I've got to ask why we'd go to the complexity without a > use case? New IOCTL would add extra complexity, which isn't necessary. Thanks, -- Tadeusz