On 03/09/16 at 10:07am, Kees Cook wrote: > On Wed, Mar 9, 2016 at 5:40 AM, Baoquan He <b...@redhat.com> wrote: > > On 03/08/16 at 10:24am, Kees Cook wrote: > >> On Mon, Mar 7, 2016 at 9:34 PM, Baoquan He <b...@redhat.com> 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? > > Yup, that should be right. And removing > CONFIG_RANDOMIZE_BASE_MAX_OFFSET will be a nice clean up, actually. It > can be its own patch separate from the rest of the changes. The config > was likely never needed (the Kconfigs already default to max values), > but I had it there out of a desire to make everything configurable > early on when it was a new feature.
OK, will check code and make a separate patch to fix this as you suggested. Thanks. Baoquan
