[PATCH V2] mkimage: fit: Do not tail-pad fitImage with external data

[Marek Vasut]

On 5/5/20 7:50 PM, Tom Rini wrote:
> On Tue, May 05, 2020 at 06:39:58PM +0200, Marek Vasut wrote:
>> On 5/5/20 6:37 PM, Alex Kiernan wrote:
>>> On Tue, May 5, 2020 at 2:28 PM Marek Vasut <marex at denx.de> wrote:
>>>>
>>>> On 5/5/20 3:22 PM, Alex Kiernan wrote:
>>>>> On Mon, May 4, 2020 at 12:28 PM Tom Rini <trini at konsulko.com> wrote:
>>>>>>
>>>>>> On Fri, May 01, 2020 at 05:40:25PM +0200, Marek Vasut wrote:
>>>>>>
>>>>>>> There is no reason to tail-pad fitImage with external data to 4-bytes,
>>>>>>> while fitImage without external data does not have any such padding and
>>>>>>> is often unaligned. DT spec also does not mandate any such padding.
>>>>>>>
>>>>>>> Moreover, the tail-pad fills the last few bytes with uninitialized data,
>>>>>>> which could lead to a potential information leak.
>>>>>>>
>>>>>>> $ echo -n xy > /tmp/data ; \
>>>>>>>       ./tools/mkimage -E -f auto -d /tmp/data /tmp/fitImage ; \
>>>>>>>       hexdump -vC /tmp/fitImage | tail -n 3
>>>>>>>
>>>>>>> before:
>>>>>>> 00000260  61 2d 6f 66 66 73 65 74  00 64 61 74 61 2d 73 69  |a-offset.data-si|
>>>>>>> 00000270  7a 65 00 00 78 79 64 64                           |ze..xydd|
>>>>>>>                    ^^       ^^ ^^
>>>>>>> after:
>>>>>>> 00000260  61 2d 6f 66 66 73 65 74  00 64 61 74 61 2d 73 69  |a-offset.data-si|
>>>>>>> 00000270  7a 65 00 78 79                                    |ze.xy|
>>>>>>>
>>>>>>> Signed-off-by: Marek Vasut <marex at denx.de>
>>>>>>> Reviewed-by: Simon Glass <sjg at chromium.org>
>>>>>>> Cc: Heinrich Schuchardt <xypron.glpk at gmx.de>
>>>>>>> Cc: Tom Rini <trini at konsulko.com>
>>>>>>
>>>>>> Applied to u-boot/master, thanks!
>>>>>>
>>>>>
>>>>> This breaks booting on my board (am3352, eMMC boot, FIT u-boot,
>>>>> CONFIG_SPL_LOAD_FIT). Not got any useful diagnostics - if I boot it
>>>>> from eMMC I get nothing at all on the console, if I boot over ymodem
>>>>> it stalls at 420k, before continuing to 460k. My guess is there's some
>>>>> error going to the console at the 420k mark, but obviously it's lost
>>>>> in the ymodem... I have two DTBs in the FIT image, 420k would about
>>>>> align to the point between them.
>>>>
>>>> My bet would be on some padding / unaligned access problem that this
>>>> patch uncovered. Can you take a look ?
>>>
>>> Seems plausible. With this change my external data starts at 0x483 and
>>> everything after it is non-aligned:
>>
>> Should the beginning of external data be aligned ?
> 
> If in U-Boot we revert e8c2d25845c72c7202a628a97d45e31beea40668 does the
> problem go away?  If so, that's not a fix outright, it means we need to
> dig back in to the libfdt thread and find the "make this work without
> killing performance everywhere all the time" option.

Still, my question is, should the beginning of external data be aligned
? And if so, to what, 4 bytes like FDT entries OR 8 bytes to cater for
arm64/rv64 ?