[PATCH] Revert "Fix data abort caused by mis-aligning FIT data"

[Alex G.]

On 10/20/20 10:54 AM, Tom Rini wrote:
> On Tue, Oct 20, 2020 at 09:38:52AM -0500, Alex G. wrote:
>> On 10/20/20 9:32 AM, Tom Rini wrote:
>>> On Tue, Oct 20, 2020 at 04:29:36PM +0200, Marek Vasut wrote:
>>>> On 10/20/20 4:07 PM, Tom Rini wrote:
>>>>> On Tue, Oct 20, 2020 at 11:05:40AM +0200, Marek Vasut wrote:
>>>>>> On 10/20/20 2:27 AM, Reuben Dowle wrote:
>>>>>>>>> What assumptions? Any code that assumes 4 byte alignment will also work
>>>>>>>> on 8 byte alignment.
>>>>>>>>>
>>>>>>>>> Reverting is not the same as assuming ALIGN(...4) if incoming data is not
>>>>>>>> already aligned to 4 bytes (as was the case when I saw crashes).
>>>>>>>>
>>>>>>>> Can the incoming data _not_ be 4 byte aligned ?
>>>>>>>> How can this be replicated ?
>>>>>>>
>>>>>>> In my case I have an offline signing process (separate from build server to keep secure boot keys safe), and this runs a script which also patches the main uboot device tree with some extra properties, then updates main uboot dtb with kernel signature, then finally updates the spl dtb with the uboot signature. I think when mkimage patches the dtb with the signatures, this results in the alignment issues (the unsigned bootloader direct from the uboot make process does not experience this issue).
>>>>>>>
>>>>>>> Possibly using mkimage to add padding would also fix the alignment issue I see at boot time.
>>>>>>>
>>>>>>>>> Interesting. I had not noticed the -B parameter previously. I had originally
>>>>>>>> fixed this issue on an older version of uboot that did not have that option,
>>>>>>>> and later rebased the fix to newer uboot. I would need to do some testing to
>>>>>>>> see if this would fix it as well.
>>>>>>>>
>>>>>>>> I believe this is the way to handle this if you are building a custom DT for U-
>>>>>>>> Boot -- just make sure it has the correct parameters. I think this is also related
>>>>>>>> to:
>>>>>>>> 20a154f95b ("mkimage: fit: Do not tail-pad fitImage with external data")
>>>>>>>
>>>>>>> I will look into this, although unfortunately I am very busy with other projects right now so can't retest th
>>>>>>
>>>>>> In that case, I would propose to revert this to fix existing boards in
>>>>>> mainline, and if your tests are not successful, revisit this issue.
>>>>>>
>>>>>> I am rather sure what you are hitting is related to the mkimage patch
>>>>>> above, there was a lengthy discussion on that topic before.
>>>>>
>>>>> This gets back to what I was saying earlier in this thread.  But to
>>>>> expand on it, we have been, but cannot, use the same variable for both
>>>>> "this is where we have the DTB at runtime to use" and "this is where the
>>>>> DTB happens to exist when we get here".  For the case of "we copy the
>>>>> device tree to $address", $address must be 8 bytes aligned.  For the
>>>>> case of "we use an externally provided DTB in place" I don't like the
>>>>> idea of, and worry a lot about, assuming it's going to be 8 byte
>>>>> aligned.  But I can set that aside for the moment.  That said, in that
>>>>> second case we need to set $address to where the device tree is.
>>>>
>>>> I don't think I understand this paragraph at all ?
>>>
>>> OK.  Maybe I can better explain it after you walk through how changing
>>> the "copy the DTB to this address" to be 8 byte aligned is leading to
>>> failure, as I ask below.
>>
>> (gdb) print gd->fdt_blob
>> $13 = (const void *) 0xc01cf85c
>> (gdb) x/4x gd->fdt_blob
>> 0xc01cf85c:    0xc01b814c     0xedfe0dd0     0xa0670100     0x38000000
>>
>> Notice how u-boot thinks fdt_blob is at 0xc01cf85c. However it was actually
>> loaded at 0xc01cf860, as evidenced by the doodfeed signature. This is with
>> the 8-byte alignment.
> 
> Ah, thanks.  So we're in this part of the code (conditions changed to results):
>          if (TRUE) {
>                  debug("%s: cannot find FDT node\n", __func__);
> 
>                  /*
>                   * U-Boot did not find a device tree inside the FIT image. Use
>                   * the U-Boot device tree instead.
>                   */
>                  if (TRUE)
>                          memcpy((void *)image_info.load_addr, gd->fdt_blob,
>                                 fdt_totalsize(gd->fdt_blob));
>   
> 
> So, our destination is what changed but gd->fdt_blob is 4 lower than the
> correct value.  Isn't that the problem?  Or am I missing something
> still?  Thanks!

That is incorrect:

	node = 465;
	...
	} else { 

		ret = spl_load_fit_image(info, sector, fit, base_offset,
				node,&image_info);

I think there is confusion between the writer of the FDT and the reader. 
This code is in SPL, the writer. It writes the FDT to an address I shall 
call x1. The reader, which is u-boot TPL, will look at address x2.

It's obvious that for the FDT to be passed successfully, x1 == x2


## For x1:

image_info.load_addr = ALIGN(spl_image->load_addr + spl_image->size, 8);

	(gdb) print/x (spl_image->load_addr + spl_image->size)
	$19 = 0xc01cf85c
	(gdb) print/x image_info->load_addr
	$20 = 0xc01cf860

x1 is 0xc01cf860


## For x2:

	__weak void *board_fdt_blob_setup(void)
	{
		/* FDT is at end of image */ 

		fdt_blob = (ulong *)&_end;

	(gdb) print &_end
	$22 = (char (*)[]) 0xc01cf85c

x2 = 0xc01cf85c

As I have hopefully demonstrated, SPL and TPL do _not_ agree on the 
location of the FDT, hence the failure.

Alex