Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH] tpm: add support for partial reads
To:     James Bottomley <James.Bottomley@HansenPartnership.com>,
        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>
 <e8c17a40-7e5e-61e9-7088-32817766b614@intel.com>
 <1532029979.3198.4.camel@HansenPartnership.com>
From:   Tadeusz Struk <tadeusz.struk@intel.com>
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: <0b9f0bb5-6620-0499-6680-5ec595167f23@intel.com>
Date:   Thu, 19 Jul 2018 13:12:19 -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: <1532029979.3198.4.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

On 07/19/2018 12:52 PM, James Bottomley wrote:
> The ABI break is the error case as I outlined above.  We can't assume
> everyone uses the current interface without getting an error and one
> error and your hosed is a nasty failure case to change the interface
> to. 

Well, if there is a broken application out there that doesn't work today
it will not work after this change neither.

> Plus, if you assume everyone is passing 4k buffers, why would you
> even need the fragmentation case?

So that people don't need to do this anymore and we can run a
spec compliant TCTI on top of /dev/tpm<N>.

> 
>>> 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.
> So what's wrong with fragmenting in the layer above the device driver
> (in userspace) and not actually changing the kernel?

Because it is much easier to implement in the driver, and
we can run a spec compliant TCTI on top of /dev/tpm<N>.

Thanks,
-- 
Tadeusz