Re: how to do a digest on a flashed uImage ?

[Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>]

> On Jul 2, 2015, at 1:42 PM, Sascha Hauer <s.hauer@pengutronix.de> wrote:
> 
> Hi Philippe,
> 
> On Wed, Jul 01, 2015 at 09:02:28AM +0200, Philippe Leduc wrote:
>> Hello,
>> 
>> I have a uImage saved in a memory partition and I am able to boot on
>> it with bootm command. I would like to add a digest (like a
>> hmac(sha1)) in order to check the integrity of the binary before
>> booting on it.
>> 
>> Because my partition is bigger than my uImage, I don't know how to use
>> digest on it.
>> In fact there are two problems that I don't know how to solve: I can't
>> get the size of my file and I can't ask digest to work on COUNT bytes.
>> 
>> For the size problem: I can extract the size of the uImage in binary
>> form since this information is present in the uImage header (via
>> memcpy), but I don't know how to convert it in a format compatible
>> with Hush.
>> 
>> For digest, I can copy the binary in the RAM, but I fear that it is
>> longer than working on the flash: it takes 4,8s to memcpy the uImage
>> in a RAM file, and less than 3s to bootm on the flash. But
>> 
>> 
>> Do you know a way to get the size of a file? Or to convert a binary
>> size into a "human readable format" for Hush? Or should I develop a
>> kind of "stat" utility for barebox?
>> Thank you in advance,
> 
> I can't think of a way on the shell to accomplish this. Something that
> might come close is uImagefs. You can mount an uImage as a filesystem,
> then you can run digest on the individual contents of the image, but not
> of the whole image itself.
> 
> Also extracting the size from the image via memcpy and somehow convert
> the value to hex, then memcpy the uImage to a file sounds fragile. I
> would probably add a option to the uimage command, like -c for copy.
> In C it's easy to sanity check the size you read and to verify the
> header checksum before doing anything else. You can't do that in shell.

uImageFS was design exactly for this case

Best Regards,
J.

> 
> Sascha
> 
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