[PATCH] arm64: mm: account for hotplug memory when randomizing the linear region

[Will Deacon]

On Wed, Oct 14, 2020 at 10:18:57AM +0200, Ard Biesheuvel wrote:
> As a hardening measure, we currently randomize the placement of
> physical memory inside the linear region when KASLR is in effect.
> Since the random offset at which to place the available physical
> memory inside the linear region is chosen early at boot, it is
> based on the memblock description of memory, which does not cover
> hotplug memory. The consequence of this is that the randomization
> offset may be chosen such that any hotplugged memory located above
> memblock_end_of_DRAM() that appears later is pushed off the end of
> the linear region, where it cannot be accessed.
> 
> So let's limit this randomization of the linear region to ensure
> that this can no longer happen, by using the CPU's addressable PA
> range instead. As it is guaranteed that no hotpluggable memory will
> appear that falls outside of that range, we can safely put this PA
> range sized window anywhere in the linear region.
> 
> Cc: Anshuman Khandual <anshuman.khandual at arm.com>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Will Deacon <will at kernel.org>
> Cc: Steven Price <steven.price at arm.com>
> Cc: Robin Murphy <robin.murphy at arm.com>
> Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
> ---
> Related to discussion here:
> https://lore.kernel.org/linux-arm-kernel/1600332402-30123-1-git-send-email-anshuman.khandual@arm.com/

Anshuman, can you fold this one into your series, please?

Will