On Fri, Jan 12, 2018 at 10:31:52AM +0800, Baoquan He wrote: >On 01/11/18 at 10:04am, Kees Cook wrote: >> On Thu, Jan 11, 2018 at 1:00 AM, Baoquan He <b...@redhat.com> wrote: >> > Hi Luiz, >> > >> > On 01/04/18 at 11:21am, Luiz Capitulino wrote: >> >> Having a generic kaslr parameter to control where the kernel is extracted >> >> is one solution for this problem. >> >> >> >> The general problem statement is that KASLR may break some kernel features >> >> depending on where the kernel is extracted. Two examples are hot-plugged >> >> memory (this series) and 1GB HugeTLB pages. >> >> >> >> The 1GB HugeTLB page issue is not specific to KVM guests. It just happens >> >> that there's a bunch of people running guests with up to 5GB of memory and >> >> with that amount of memory you have one or two 1GB pages and is easier for >> >> KASLR to extract the kernel into a 1GB region and split a 1GB page. So, >> >> you may not get any 1GB pages at all when this happens. However, I can >> >> also >> >> reproduce this on bare-metal with lots of memory where I can loose a 1GB >> >> page from time to time. >> >> >> >> Having a kaslr_range= parameter solves both issues, but two major >> >> drawbacks >> >> is that it breaks existing setups and I guess users will have a very hard >> >> time choosing good ranges. >> >> >> >> Another idea would be to have a CONFIG_KASLR_RANGES, where each arch >> >> could have a list of ranges known to contain holes and/or immovable >> >> memory and only extract the kernel into those ranges. >> > >> > If add CONFIG_KASLR_RANGES, then a distro like RHEL will have this range >> > always, whether people need hugetlb or not. >> > >> > So in this case, what range do we need to avoid? Only [1G, 2G]? >> >> Any ranges like that that need to be avoided should be known at build >> time, so they should simply be added to the mem_avoid list that is >> already present in the KASLR code... > >Seems KASLR doesn't have an solution which allow user to specify avoided >range for kernel text KASLR stage only. The memmap="!#$" can add range to >mem_avoid, while it will make them not added to e820. >
How about adding a new option, like "huge_page=nn@ss". Fill the regions to mem_avoid. But this parameter will only be parsed in kaslr period. The followed handlling of memmap will not be excuted. Thanks, Chao Fan >Here like this hugetlb case, Luiz wants kernel to avoid the [2G, 3G) >candidate position for hugetlb allocation, meanwhile wants it to be >added to mm subsystem later. > >Thanks >Baoquan > > >
