Messages in this thread | | | Date | Fri, 20 Oct 2017 10:45:42 +0200 | From | Michal Hocko <> | Subject | Re: [PATCH 2/2] fs, elf: drop MAP_FIXED from initial ET_DYN segment |
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On Thu 19-10-17 10:19:40, Kees Cook wrote: > On Thu, Oct 19, 2017 at 4:20 AM, Michal Hocko <mhocko@kernel.org> wrote: > > On Tue 17-10-17 13:01:04, Kees Cook wrote: > >> On Tue, Oct 17, 2017 at 2:04 AM, Michal Hocko <mhocko@kernel.org> wrote: > > [...] > >> > I am not insisting on this patch but it seems to me is just makes a > >> > recoverable state a failure. > >> > >> Right, I understand you're trying to make it recoverable. I'm > >> suggesting that making it recoverable provides a way for an attack to > >> abuse it, and that what we'd be recovering from is a case we should > >> never ever see. > >> > >> Consider the case where through some future bug/feature, it's possible > >> to put the stack at an arbitrary location during an exec. (We've > >> worked to fix that already, but who knows what the future holds either > >> through misfeatures or bugs.) If an attacker maps the stack over a > >> large portion of the PIE exec range, patch 2 will result in vmmap > >> searching out a location that isn't already allocated. This means that > >> instead of the PIE ASLR choosing from the entire possible range, it > >> will get limited to only the area where something isn't already > >> overlapping. This would give an attacker the ability to control the > >> PIE ASLR, possibly forcing it into a fixed location. > > > > Yes, I guess I understand that part. What is not clear to me exactly is > > why this matters as we have the mmap_base randomized and not under the > > control of the attacker. > > mmap_base is separate from the PIE base, so patch 2 would allow for a > reduction of the PIE ASLR entropy in the case of a novel overlap > attack.
OK, it seems that I am just too dull see through your concerns here. Anyway, are you willing to ack the patch 1 (when metag fix is included)? I would resubmit in that case and ask for merging without patch 2. -- Michal Hocko SUSE Labs
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