Messages in this thread | | | Date | Fri, 6 Nov 2015 15:49:16 -0800 | Subject | Re: [PATCH] arm: Use kernel mm when updating section permissions | From | Kees Cook <> |
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On Fri, Nov 6, 2015 at 3:41 PM, Laura Abbott <labbott@redhat.com> wrote: > On 11/06/2015 12:46 PM, Russell King - ARM Linux wrote: >> >> On Fri, Nov 06, 2015 at 10:44:32AM -0800, Laura Abbott wrote: >>> >>> with my test patch. I think setting both current->active_mm and &init_mm >>> is sufficient. Maybe explicitly setting swapper_pg_dir would be cleaner? >> >> >> Please, stop thinking like this. If you're trying to change the kernel >> section mappings after threads have been spawned, you need to change >> them for _all_ threads, which means you need to change them for every >> page table that's in existence at that time - you can't do just one >> table and hope everyone updates, it doesn't work like that. >> > > That's a bad assumption assumption on my part based on what I was > observing. At the time of mark_rodata_ro, the only threads present > are kernel threads which aren't going to have task->mm. Only the > running thread is going to have active_mm. None of those are init_mm. > To be complete we need: > > - Update every task->mm for every thread in every process > - Update current->active_mm > - Update &init_mm explicitly > > All this would need to be done under stop_machine as well. Does that cover > everything or am I still off?
I still think we need to find an earlier place to do this. :(
-Kees
-- Kees Cook Chrome OS Security
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