[RFC PATCH] arm64/acpi: disallow AML memory opregions to access kernel memory

[Jason A. Donenfeld]

Hmm, actually...

> >         if (memblock_is_map_memory(phys))
> > -               return (void __iomem *)__phys_to_virt(phys);
> > +               return NULL;

It might be prudent to have this check take into account the size of
the region being mapped. I realize ACPI considers it to be undefined
if you cross borders, but I could imagine actual system behavior being
somewhat complicated, and a clever bypass being possible.
Hypothetically: KASLR starts kernel at phys_base+offset, [phys_base,
rounddownpage(offset)) doesn't get mapped, malicious acpi then maps
phys_base+rounddownpage(offset)-1, and then this check doesn't get
hit.