Re: [PATCH v3 16/19] x86, kaslr: Randomize physical and virtual address of kernel separately

[Baoquan He]

On 03/08/16 at 10:24am, Kees Cook wrote:
> On Mon, Mar 7, 2016 at 9:34 PM, Baoquan He <bhe@xxxxxxxxxx> wrote:
> >> It seems like CONFIG_RANDOMIZE_BASE_MAX_OFFSET should have been
> >> eliminated when the on-demand page table code was added. Once that was
> >> added, there's no physical max any more. And virtual randomization
> >> should have no max at all.
> > For physically random, yes, CONFIG_RANDOMIZE_BASE_MAX_OFFSET is not
> > needed anymore. But for virtually random,
> > CONFIG_RANDOMIZE_BASE_MAX_OFFSET is still mandatory since kernel text
> > mapping and kernel module mapping share the 2G virtual address space as
> > follows. Though kaslr increase kernel text mapping from 512M to 1G, it's
> > still limited, can't exceed CONFIG_RANDOMIZE_BASE_MAX_OFFSET.
> >
> > [0xffffffff80000000, 0xffffffffffffffff]
> >
> > But now as you suggested, I would like to change
> > CONFIG_RANDOMIZE_BASE_MAX_OFFSET to another name because it's only
> > valid for virtual randomization. A more specific name is better.
> 
> Yes, right, the virtual has a 1G max, but I meant that it doesn't need
> to be a CONFIG item any more. Physical can use physical memory max as
> its max, and virtual max can now be calculated from the existing text
> mapping size.

Got it, it should be KERNEL_IMAGE_SIZE instead, right?