On Mon, Aug 14, 2017 at 2:53 PM, Ard Biesheuvel
[off-list ref] wrote:

This series implements randomization of the placement of the core ARM kernel
inside the lowmem region. It consists of the following parts:

- changes that allow us to build vmlinux as a PIE executable which retains
  the metadata required to fix up all absolute symbol references at runtime
- changes that eliminate absolute references from low-level code that may
  execute with the MMU off: this removes the need to perform explicit cache
  maintenance after the absolute references have been fixed up at runtime with
  the caches enabled
- changes to the core kernel startup code to take the physical offset into
  account when creating the virtual mapping (the pa-to-va mapping remains
  unchanged)
- changes to the decompressor to take the KASLR offset into account when
  placing the kernel in physical memory
- changes to the UEFI stub code to choose the KASLR offset and communicate
  it to the decompressor

Would it make sense to also randomize the pa-to-va mapping on top of this?
That can certainly be a later follow-up, I'm just trying to think of the options
we have, given that the kernel is now relocatable and we can support arbitrary
pa-to-va mappings already.

Can you explain how the random seed is passed from the bootloader
to the kernel when we don't use EFI? Is this implemented at all? I see
that you add a seed to "/chosen/kaslr-seed" in the EFI stub when using
the EFI boot services, but I don't see where that value gets read again
when we relocate the kernel.

      Arnd