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

[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.

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

Regards,
Simon