[BUG] fdt_pack_reg in common/fdt_support.c can cause crash from unaligned access

[David Virag]

Hi,

I'm trying to port U-Boot to a new board (Samsung JACKPOTLTE, ARMv8,
Exynos7885) but when CONFIG_ARCH_FIXUP_FDT_MEMORY is enabled, the bootm
command leads to an unaligned memory access, which results in a
synchronous abort.

After a long debugging session, I concluded that fdt_pack_reg in
common/fdt_support.c writes to unaligned addresses in its for loop.
In the case of address_cells being 2, and size_cells being 1, the
buffer pointer gets incremented by 12 in each loop, making the second
iteration (i=1) write a 64bit value to a non 64bit aligned address.

Turning the alignment check enable bit (A) off in SCTLR makes the
function work as intended. I couldn't find code that touches this bit,
but I may have missed something. I don't think writing in two parts
should be the fix, but something should be done about this. As far as I
understand, any arm64 board that has this bit turned on, either from
previous code or just the initial status of the bit after power on,
could crash here.

This is on top of the latest commit as of now
(0beb649053b86b2cfd5cf55a0fc68bc2fe91a430)

What should be done here?

Best regards,
David