Date:	Tue, 14 Jun 2016 21:05:43 +0000
From:	"Winkler, Tomas" <tomas.winkler@...el.com>
To:	"arve@...roid.com" <arve@...roid.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	"Hunter, Adrian" <adrian.hunter@...el.com>,
	"James Bottomley" <James.Bottomley@...senpartnership.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Vinayak Holikatti <vinholikatti@...il.com>,
	Andy Lutomirski <luto@...nel.org>,
	Michael Ryleev <gmar@...gle.com>,
	"Joao Pinto" <Joao.Pinto@...opsys.com>,
	Christoph Hellwig <hch@....de>,
	Yaniv Gardi <ygardi@...eaurora.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>
Subject: RE: [PATCH v4 0/8] Replay Protected Memory Block (RPMB) subsystem

>>> wrote:
>>> > Few storage technology such is EMMC, UFS, and NVMe support RPMB
>>> >hardware partition with common protocol and frame layout.
>>> > The RPMB partition cannot be accessed via standard block layer, but
>>> >by a set of specific commands: WRITE, READ, GET_WRITE_COUNTER, and
>>> >PROGRAM_KEY.
>>> >...
>>>
>>> If the same protocol is used by all these standards, why not export it directly
>>> (including the RESULT_READ command or not even knowing the command
>>> types)?
>> The protocol is the  same, but the wrapping of the packets is storage type specific so
>> I believe that the best abstraction is on those  4 operations level. I'm not sure if the code would
>> be simpler if it would be exposed on a lower level.
>
> I disagree. With the two storage types you support, the packets are
> identical. The only difference is the low level commands you use to
> send and receive them.
The packets are identical, but there are these little settings you need to be aware of
like set argument  31 in CMD23 for WRITE and PROGRAM_KEY and for others not so
the storage type transparency is lost, actually the UFS protocol is a bit cleaner in that sense.
I know it can be ironed somehow, but this just stresses the point. 

>> RESULT_READ  is  a command to be issued for getting preceeding write operation status, it's a kind of work around about the fact that you have to issue a read operation
>> in order to retrieve data in this case a  write operation result.  It can be successfully hidden and final result of the operation is delivered
>> to the user.
>>
>
> Yes, it is possible to hide the result read command, but that does not
> mean you should. The rpmb protocol is designed to let two endpoints
> communicate in a way that lets them detect tampering. While the packet
> you inject does not contain any protected data, you can still view it
> as a form of tampering. 

I’m not seeing it like injecting packets, those are merely commands embedded in the packets that need to be performed in order to complete the operation
and there is not security value in them, the only end to end protection is truly given by the MAC verification and this is preserved. 

>If a future rpmb protocol version adds
> features, you could loose the ability to inject packets.

The code will have to change anyhow.  

>
>>> While I would prefer an rpmb specific interface over the existing raw
>>> mmc command interface, all I need is an rpmb operation that lets me send
>>> and receive buffers without interruption.
>>
>> I currently don't see an obstacle on doing the same with proposed interface, what is the issue are seeing.
>>
>
> The main issue is that you are injecting commands, so code that
> follows the mmc spec will not work.

Yes, it should be storage type independent, not mmc spec dependant. 
The interface reduces the number of data passed between user space and kernel, the device power management is simpler. 

>
>>> You can find our exiting user-space code here at
>>> https://android.googlesource.com/platform/system/core/+/master/trusty/s
>>> torage/proxy/rpmb.c.
>>> If you use an interface more similar to this, I think your emmc and ufs
>>> specific code would be simpler. Also, if you don't need the in-kernel
>>> interface, the kernel would not need to know the details of the rpmb
>>> protocol at all.
>>
>> My major interest is the in-kernel protocol the user space API was more intended for debug, but I found it would be even more useful.
>> The store type  access is very RPMB specific  for both MMC and UFS and needs to do special operations for RPMB so I don't see how this awareness can be removed or I'm not reading your proposal correctly.
>
> The interface we use specifies reliable-write, write and read
> operations on an rpmb partition. I don't think you need to know more
> than this in either mmc or ufs. I have not seen the ufs spec, but
> based on your code it looks like reliable-write and write can map to
> the same command there.
Yes, the interface can be also abstract on let’s call it raw rpmb packet read/write level, but I didn’t see the value in at the time as RPMB operations and the steps are well defined.
Maybe there is a place for to support for fing grained access or at leasting adding RESULT_READ command as well,  for the usecases like yours.

>> Accessing RPMB is a multiple stepsoperation, the steps can be driven from the user space as done in EMMC ioctl but hidning would reduce the number of system calls and amount of data passed,
>> in some sense the same as in the  new mmc  MMC_IOC_MULTI_CMD is trying ot achive.
>>
> The main purpose of using the MMC_IOC_MULTI_CMD is not to reduce the
> number of syscalls. It is to prevent other mmc operations from getting
> interleaved with the rpmb packets. Some emmc chips will only respond
> error packet if any other partitions are read from between the write
> and read operation on the rpmb partition.

I didn’t encountered as our interface doesn’t suffer form that issue but yes this just another reason to use the new rpmb interface
>
>>> I have not tested your code, but it looks like we would have to modify the
>>> storage proxy to interpret the data it currently passes through and remove all
>>> RESULT_READ packets.
>> Your proxy driver just sends ioctls so this wouldn't be much difference and the rpmb code on the trusty w need rewrite just rpmb_send () function,
>> actually removing one set of buffer size. I will try to make that modification if it helps?
>>
>
> No I don't want you to modify the code that runs in the secure OS.
> This would require additional code in boot loaders and proxy servers
> using the existing MMC_IOC_MULTI_CMD command as they too would have to
> interpret the packets to inject RESULT_READ packets.

I’ve looked at the proxy and and secure OS, the rewirte is not so hard, though.
I really cannot figure to boo loader and secure OS interactions, you have this notion of TP and TDEA ports but those are not used from the secure OS. 
Is there a software you can point me to? 

Second if it won’t be possible to use the current implementation if the storage type change UFS or NVMe anyhow and on the othernad
I’m not suggesting to kill MMC ioctl, so this won’t be breackages of the existing software. 

In bottom line I will try to add raw read/write access to RPMB to support fine grained access and see if you can work with that.


I really appreciate your feedback.
Thanks
Tomas 

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