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

[Marek Vasut]

On 5/6/20 4:27 PM, Tom Rini wrote:
> On Wed, May 06, 2020 at 04:17:35PM +0200, Marek Vasut wrote:
>> On 5/6/20 3:48 PM, Tom Rini wrote:
>>> 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 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.
>>>>
>>>> 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).
>>
>> Why 8-byte alignment ? The external data are copied into the target
>> location, so why do they need to be padded in any way?
> 
> The start of the external data needs the alignment, to be clearer.

Why ?

>> If the external data are used in place, then it's the same problem as
>> arm64 fitImage with fdt_high=-1, which fails because the DT is aligned
>> to 4 bytes and arm64 expects it at 8byte offset.
> 
> Except we're talking about cases where we can't relocate the data or it
> doesn't make any sense to.

Which cases? This really needs to be spelled out.

> That said, if you think the answer is that we need to ensure that when
> we use external data we first align it, please show us how that looks.

I would like to understand the problem space first.