[PATCH v3] mkimage: Default to 8-byte alignment for DTBs added via -b argument

[Marek Vasut]

On 1/26/26 6:38 PM, Sean Anderson wrote:
> On 1/23/26 05:51, Marek Vasut wrote:
>> On 1/23/26 11:40 AM, Anshul Dalal wrote:
>>> Hi Marek,
>>>
>>> On Fri Jan 23, 2026 at 3:57 PM IST, Marek Vasut wrote:
>>>> On 1/23/26 4:32 AM, Beleswar Prasad Padhi wrote:
>>>>>
>>>>> On 23/01/26 00:33, Marek Vasut wrote:
>>>>>> On 1/22/26 6:45 PM, Tom Rini wrote:
>>>>>>> On Thu, Jan 22, 2026 at 10:52:47PM +0530, Beleswar Padhi wrote:
>>>>>>>
>>>>>>>> When CONFIG_SPL_MULTI_DTB_FIT is enabled, multiple device trees are
>>>>>>>> packed inside the multidtb.fit FIT image. While the individual DTBs
>>>>>>>> and the FIT image start address are 8-byte aligned, the DTBs embedded
>>>>>>>> within the FIT image are not guaranteed to maintain 8-byte alignment.
>>>>>>>>
>>>>>>>> This misalignment causes -FDT_ERR_ALIGNMENT failure in
>>>>>>>> setup_multi_dtb_fit() when locating the next available DTB within the
>>>>>>>> FIT blob and setting gd->fdt_blob, because of the recent libfdt
>>>>>>>> hardening since commit 0535e46d55d7 ("scripts/dtc: Update to upstream
>>>>>>>> version v1.7.2-35-g52f07dcca47c")
>>>>>>>>
>>>>>>>> The mkimage tool already supports enforcing this alignment via the -B
>>>>>>>> option, but users would have to specify it explicitly. This change
>>>>>>>> makes 8-byte alignment the default when using -b.
>>>>>>>>
>>>>>>>> Reported-by: Anshul Dalal <anshuld at ti.com>
>>>>>>>> Closes: https://cas5-0-urlprotect.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2flore.kernel.org%2fu%2dboot%2fDFJ950O0QM0D.380U0N16ZO19E%40ti.com&umid=003810bd-b0e0-4a71-9348-75ffbe5cbae5&rct=1769167692&auth=d807158c60b7d2502abde8a2fc01f40662980862-3859cf23dac8d65722a0a9ed4c40c98c98a297de
>>>>>>>> Fixes: 0535e46d55d7 ("scripts/dtc: Update to upstream version v1.7.2-35-g52f07dcca47c")
>>>>>>>> Signed-off-by: Beleswar Padhi <b-padhi at ti.com>
>>>>>>>
>>>>>>> Tested-by: Tom Rini <trini at konsulko.com>
>>>>>> Doesn't this enable 8-byte alignment for everything in case a DT is specified on mkimage command line ? That doesn't seem right ?
>>>>>>
>>>>>> If I do mkimage -f auto -b ...dtb ... , then I only want the DTB to be 8-byte aligned, all the other blobs can be 4 byte aligned just fine .
>>>>>
>>>>>
>>>>> All the mkimage flags are parsed at once and populated in the params
>>>>> data structure in one shot in the code. There is no separation of code
>>>>> specifically for generating a FIT for a DTB vs for anything else.
>>>>
>>>> That does not seem to be true ?
>>>>
>>>> $ git grep -p '\<bl_len\>' tools/
>>>> tools/fit_image.c=static int fit_extract_data(struct image_tool_params
>>>> *params, const char *fname)
>>>> tools/fit_image.c:      align_size = params->bl_len ? params->bl_len : 4;
>>>> ...
>>>>
>>>> So something like that may work ?
>>>>
>>>> "
>>>> diff --git a/tools/fit_image.c b/tools/fit_image.c
>>>> index 0306333141e..0c606ba4cc3 100644
>>>> --- a/tools/fit_image.c
>>>> +++ b/tools/fit_image.c
>>>> @@ -642,9 +642,15 @@ static int fit_extract_data(struct
>>>> image_tool_params *params, const char *fname)
>>>>            for (node = fdt_first_subnode(fdt, images);
>>>>                 node >= 0;
>>>>                 node = fdt_next_subnode(fdt, node)) {
>>>> -               const char *data;
>>>> +               const char *data, *type;
>>>>                    int len;
>>>>
>>>> +               if (align_size < 8) {
>>>> +                       type = fdt_getprop(fdt, node, FIT_TYPE_PROP, &len);
>>>> +                       if (type && !strcmp(type, "flat_dt"))
>>>> +                               align_size = 8;
>>>> +               }
>>>> +
>>>>                    data = fdt_getprop(fdt, node, FIT_DATA_PROP, &len);
>>>>                    if (!data)
>>>>                            continue;
>>>> "
>>>>
>>>
>>> I just ran a quick test with this diff and it seems to fix the issue for
>>> us. If it's okay can we take the change as is.
>> I think the strcmp needs to be some strncmp and check the 'len' too.
>>
>> Let's see what others think.
> 
> strcmp is fine when one of the strings is a constant
> 
> If type is shorter than "flat_dt" then there is no risk of overflow.

What exact data would you be comparing here , the constant and something 
read from possibly past the user supplied "type" buffer ?

Some validation of "len" has to be done before it is fed into strcmp() here.