[U-Boot] U-Boot TFTP protection

Hello, We have been looking at protecting U-Boot from (malicious) TFTP overwrites. We want to do this after our ARMv7 U-Boot has relocated.

The memory map looks like this (I hope):

--------------------------- Top of DRAM | U-Boot (Protected) | -------------------------- U_Boot_start | Heap (Protected) | -------------------------- Start_Heap = U_Boot_start - Heap_Size | Stack (Protected) | -------------------------- Start_Stack = Start_Heap - Stack_Size | Buffers (Protected) | -------------------------- ??? | Free DRAM (Not Protected) --------------------------- Start of DRAM

I seem to get lost in the code trying to find possible buffers, can you please give a hint how I can find the address "???"

Best Regards, Stefan