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

[Tom Rini <trini@konsulko.com>]

On Tue, May 05, 2020 at 07:53:42PM +0200, Marek Vasut wrote:
> 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@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.
> 
> 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 ?

Is "external data" the kernel in this case?  If so, I swear Linux
mandates 8 byte alignment for arm32 as well.

-- 
Tom
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