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

[Michael Walle <michael@walle.cc>]

Am 2020-05-05 23:17, schrieb 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@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@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@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@denx.de>
>>> > >>>>> Reviewed-by: Simon Glass <sjg@chromium.org>
>>> > >>>>> Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
>>> > >>>>> Cc: Tom Rini <trini@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.

Here are the steps to reproduce it on the uboot master branch:

$ CROSS_COMPILE=arm-linux-gnueabihf- make pico-imx6_defconfig 
fit-dtb.blob tools
$ tools/dumpimage -T flat_dt -p 1 -o fdt-1 fit-dtb.blob
$ file fdt-1
fdt-1: data
$ git revert 20a154f95bfe0a3b5bfba90bea7f001c58217536
$ git clean -fdx
$ CROSS_COMPILE=arm-linux-gnueabihf- make pico-imx6_defconfig 
fit-dtb.blob tools
$ tools/dumpimage -T flat_dt -p 1 -o fdt-1 fit-dtb.blob
$ file fdt-1
fdt-1: Device Tree Blob version 17, size=34978, boot CPU=0, string block 
size=1746, DT structure block size=33176

-michael