Hi Heiko,
Adding a size limit without breaking things turns out to be much more difficult that it would seem. So, instead of capping the size, we have changed the memory map we are using for uboot. It is probably worthwhile for others using UBISPL in a secure boot nevironment to do the same.
Traditionally, uboot SPL or TPL loads or relocates to an address near the top of memory and then builds its stack downwards from the top of memory. That means that any address we use for a volume.load_address will eventually step on something if the volume is large enough. So, we move everything down by a size that is sufficient for any image that UBISPL may need to load (32M) and place the CONFIG_SPL_LOAD_FIT_ADDRESS Above the stack where it can grow without hitting anything until it causes an exception.
I'm not sure if there is anything else to be done for this situation except to caution people implementing secure boot environments to be aware of their surroundings.
Regards,
Joel Peshkin