[U-Boot-Users] New Image format: headers hashes.

[Bartlomiej Sieka]

Hi Luigi,

You wrote:
> On gio, 2008-03-27 at 12:13 +0100, Luigi 'Comio' Mantellini wrote:
> 
>>
>> - The mkimage calculate hashes before that timestamp is added to
>> image.
>> is it better exchange the order of these operations (before add
>> timestamp then calculate hashes)?

Please see below.


>> - Does the new format assure that the complete image (_all_ sections,
>> images, ramdisks, configurations, blobs) are covered by at least an
>> hash
>> value?

Currently, the hash calculation is performed only over binary data of
component images (kernel, ramdisk, fdt, etc). In particular, timestamp
information is not protected by the hash, so the ordering of hash
calculation and timestamp addition doesn't matter.


 >> should mkimage add at least a hash value for the root node?

Adding a hash value for the root node only will not be easy. An easier
approach I think would be to add a hash value for the entire FIT image.


> In addition to the previous question:
> 
> - I'm interested to calculate and store from U-boot code but the 
> fit_image_set_hashes is compiled only when the USE_HOSTCC symbol is 
> defined. Why? Is there a particular reason?

There's no need for the function that you mention in current U-Boot
code, that's the reason why it's under USE_HOSTCC. If you're planning on
adding code to U-Boot that will use fit_image_set_hashes(), then just
remove the USE_HOSTCC #define's from around this function.


 > I think that a lot of
 > useful functions (ifdef-ed by USE_HOSTCC) should be available also in
 > u-boot code, anyway the linker will drop the unused functions.

I don't think the linker will do this in case of U-Boot:

With the following patch:

diff --git a/common/image.c b/common/image.c
index f04826a..850a9e4 100644
--- a/common/image.c
+++ b/common/image.c
@@ -1950,7 +1950,6 @@ static int calculate_hash (const void *data, int 
data_len,
  	return 0;
  }

-#ifdef USE_HOSTCC
  /**
   * fit_set_hashes - process FIT component image nodes and calculate hashes
   * @fit: pointer to the FIT format image header
@@ -2119,7 +2118,6 @@ int fit_image_hash_set_value (void *fit, int 
noffset, uint

  	return 0;
  }
-#endif /* USE_HOSTCC */

  /**
   * fit_image_check_hashes - verify data intergity


I see:

$ ${CROSS_COMPILE}nm -S common/image.o | grep fit_image_set_hashes
0000155c 000001f4 T fit_image_set_hashes
$ ${CROSS_COMPILE}nm -S common/libcommon.a | grep fit_image_set_hashes
0000155c 000001f4 T fit_image_set_hashes
$ ${CROSS_COMPILE}nm -S u-boot | grep fit_image_set_hashes
fffb1924 000001f4 T fit_image_set_hashes


There's also size increase with the patch applied:
    text    data     bss     dec     hex filename
  284615   15556  357120  657291   a078b ./u-boot

    text    data     bss     dec     hex filename
  285875   15572  357120  658567   a0c87 u-boot


HTH,
Bartlomiej