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

[Tom Rini <trini@konsulko.com>]

On Tue, May 05, 2020 at 11:17:19PM +0200, Michael Walle wrote:
> 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.
> 
> You can find the two fit-dtb.blobs here:
> 
> https://walle.cc/u-boot/fit-dtb.blob.working
> https://walle.cc/u-boot/fit-dtb.blob.non-working
> 
> 
> Reverting e8c2d25845c72c7202a628a97d45e31beea40668 doesn't help (I might
> reverted it the wrong way, there is actually a conflict).
> 
> I'll dig deeper into that tomorrow, but maybe you have some pointers where
> to look.
> 
> For reference you can find the current patch here:
> https://github.com/mwalle/u-boot/tree/sl28-upstream

I think we have a few things to fix here.  Marek's patch is breaking
things and needs to be reverted.  But it's showing a few underlying
problems that need to be fixed too:
- fit_extract_data() needs to use calloc() not malloc() so that we don't
  leak random data.
- We need to 8-byte alignment on the external data.  That's the
  requirement for Linux for device trees on both 32 and 64bit arm.
  Atish, does RISC-V require more than that?  I don't see it in Linux's
  Documentation/riscv/boot-image-header.rst (and there's no booting.rst
  file like arm/arm64).

Thanks all!

-- 
Tom
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