Subject: Re: Memory coherency on MPC8272

From: Dmitri Petchkine <[email-masked]>
Date: Fri, 22 Jun 2007 16:47:30 -0400

On 06/22/2007 03:35 PM, Dan Malek wrote:
> On Jun 22, 2007, at 10:28 AM, Dmitri Petchkine wrote:
>> My understanding that the security hardware of MPC8272 uses DMA to write
>> results into the memory which may cause a coherency problem.
> 
> Where did you get such an (incorrect) understanding?
> I suggest you acquire your understanding from reading the
> MPC8272 reference manual, since it describes the cache
> and snooping options between the SEC and memory,
> as well as among the SEC units.
> 
>> My exposure to such hardware issues is very limited, so I appreciate any
>> advice on how to fix it.
> 
> The code snippet clearly shows you don't understand
> the user/kernel interface, since your access to "param" isn't
> correct.

Please note that I'm NOT writing a driver for SEC1, I'm using it. The 
driver has been written by Freescale. The piece of code I quoted in my 
previous email and you reference to has been coded by Freescale guys. If 
you want take a look, the sources can be downloaded from

http://www.freescale.com/webapp/sps/download/license.jsp?colCode=SEC1DRVRS&location=null&fpsp=1

Before performing any crypto operation, my application calls the SEC1 
driver to allocate memory buffers (via IOCTL_MALLOC) in the kernel space 
and copy all the user buffers into the kernel space (via 
IOCTL_COPYFROM), including the request structure itself.

After the completion of the crypt op, the application copies (via 
IOCTL_COPYTO) the request structure back to the user space as well as 
all the output buffers.

 > The SEC is complex and has subtle control
> considerations, any part of this could be incorrect.  I
> suspect your coding errors are hidden/highlighted
> by adding the code for the printing, not the actual
> operation itself.

Yes it might be that I use the driver improperly. Although the app's 
interaction with it is very limited: set up a structure in the kernel 
space, do a crypto op, get data back to the user space. All of it is 
done through ioctl().

The application is a quite comprehensive unit test for crypto, which 
includes DES/TDES/AES/RC4, SHA-1/SHA-2/MD5, RSA, DSA, DH, and ECC. It 
can be built also as a kernel module - this passes all the exact same 
tests, which gives me some assurance that request structures for the 
SEC1 hardware are set properly.

Thanks
Dmitri Petchkine