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

[Alex Kiernan]

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:

/dts-v1/;
// magic: 0xd00dfeed
// totalsize: 0x483 (1155)
// off_dt_struct: 0x38
// off_dt_strings: 0x3f8
// off_mem_rsvmap: 0x28
// version: 17
// last_comp_version: 2
// boot_cpuid_phys: 0x0
// size_dt_strings: 0x8b
// size_dt_struct: 0x3c0


-- 
Alex Kiernan