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

[Alex Kiernan]

On Tue, May 5, 2020 at 7:41 PM Simon Glass <sjg at chromium.org> wrote:
>
> 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.
>

Just reading the commit log, the example in there shows the padding
after the FIT image being dropped:

    $ 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|

Though I can't reproduce that result with or without the associated commit.

--
Alex Kiernan