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

[Michael Walle]

Hi all,

Am 2020-05-05 20:41, schrieb Simon Glass:
> Hi Tom,
> 
> On Tue, 5 May 2020 at 11:50, Tom Rini <trini at konsulko.com> 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.
> 
> If it is a device tree, it must be 32-bit aligned.

This commit actually breaks my board too (which I was just about to send
upstream, but realized it was broken).

Said board uses SPL and main U-Boot. SPL runs fine and main u-boot 
doesn't
output anything. The only difference which I found is that fit-dtb.blob 
is
2 bytes shorter. And the content is shifted by one byte although
data-offset is the same. Strange. In the non-working case, the inner
FDT magic isn't 4 byte aligned.

You can find the two fit-dtb.blobs here:

https://walle.cc/u-boot/fit-dtb.blob.working
https://walle.cc/u-boot/fit-dtb.blob.non-working


Reverting e8c2d25845c72c7202a628a97d45e31beea40668 doesn't help (I might
reverted it the wrong way, there is actually a conflict).

I'll dig deeper into that tomorrow, but maybe you have some pointers 
where
to look.

For reference you can find the current patch here:
https://github.com/mwalle/u-boot/tree/sl28-upstream

> 
> But Marek's patch affects the FIT image itself, so I am not sure what
> would go after that.
> 
> Regards,
> Simon

-- 
-michael