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

[Marek Vasut]

On 1/27/26 5:38 PM, Tom Rini wrote:

>> No, the check in fdt_getprop is only for the name, not the value (which
>> could be arbitrary binary data including many nul bytes).
>>
>> I think the assumption in most of U-Boot is that the provided FDT is
>> trusted (or at least not maliciously ill-formed).  functions like
>> image_get_checksum_algo read up to 6 bytes beyond full_name if full_name
>> == "". It's possible to read off the end of the DTB if this is the very
>> last string in the strings block and there is no trailing padding. If
>> we're really concerned about this (e.g. to avoid false-positives with
>> ASAN), then we should just add (say) 16 bytes to the end of every DTB
>> when we malloc it.
> 
> Yes, we rely on the sanity checking in libfdt, which I think the kernel
> also does.
> 
> And no, I'm not sure if we care enough about all of these corner cases,
> but if we do then I'm not sure this right here and now is where to
> start. It should start with upstream libfdt to see whatever cases aren't
> handled, and then what cases fall on the callers to deal with wrt
> security implications.
> 
> Because I really, really, really, do not want to block fixing booting on
> some large number of boards because now we're going to depend first on a
> security audit here.
So back to my and Sean suggestion:

fdt_string_eq_() does effectively memcmp():

return p && (slen == len) && (memcmp(p, s, len) == 0);

So do this and be done with it ?

type = fdt_getprop(fdt, node, FIT_TYPE_PROP, &len);
if (type && len == strlen(FIT_TYPE_PROP) && !memcmp(type, "flat_dt", len))
   align_size = 8;