On Tue, Mar 27, 2018 at 6:51 AM, Ilya Smith <blackzert at gmail.com> wrote: > >> On 27 Mar 2018, at 10:24, Michal Hocko <mhocko at kernel.org> wrote: >> >> On Mon 26-03-18 22:45:31, Ilya Smith wrote: >>> >>>> On 26 Mar 2018, at 11:46, Michal Hocko <mhocko at kernel.org> wrote: >>>> >>>> On Fri 23-03-18 20:55:49, Ilya Smith wrote: >>>>> >>>>>> On 23 Mar 2018, at 15:48, Matthew Wilcox <willy at infradead.org> wrote: >>>>>> >>>>>> On Thu, Mar 22, 2018 at 07:36:36PM +0300, Ilya Smith wrote: >>>>>>> Current implementation doesn't randomize address returned by mmap. >>>>>>> All the entropy ends with choosing mmap_base_addr at the process >>>>>>> creation. After that mmap build very predictable layout of address >>>>>>> space. It allows to bypass ASLR in many cases. This patch make >>>>>>> randomization of address on any mmap call. >>>>>> >>>>>> Why should this be done in the kernel rather than libc? libc is perfectly >>>>>> capable of specifying random numbers in the first argument of mmap. >>>>> Well, there is following reasons: >>>>> 1. It should be done in any libc implementation, what is not possible IMO; >>>> >>>> Is this really so helpful? >>> >>> Yes, ASLR is one of very important mitigation techniques which are really used >>> to protect applications. If there is no ASLR, it is very easy to exploit >>> vulnerable application and compromise the system. We can?t just fix all the >>> vulnerabilities right now, thats why we have mitigations - techniques which are >>> makes exploitation more hard or impossible in some cases. >>> >>> Thats why it is helpful. >> >> I am not questioning ASLR in general. I am asking whether we really need >> per mmap ASLR in general. I can imagine that some environments want to >> pay the additional price and other side effects, but considering this >> can be achieved by libc, why to add more code to the kernel? > > I believe this is the only one right place for it. Adding these 200+ lines of > code we give this feature for any user - on desktop, on server, on IoT device, > on SCADA, etc. But if only glibc will implement ?user-mode-aslr? IoT and SCADA > devices will never get it. I agree: pushing this off to libc leaves a lot of things unprotected. I think this should live in the kernel. The question I have is about making it maintainable/readable/etc. The state-of-the-art for ASLR is moving to finer granularity (over just base-address offset), so I'd really like to see this supported in the kernel. We'll be getting there for other things in the future, and I'd like to have a working production example for researchers to study, etc. -Kees -- Kees Cook Pixel Security
