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Re: [PATCH] mm: mm, mmap: do not blow on PROT_NONE MAP_FIXED holes in the stack

From	Michal Hocko <mhocko@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH] mm: mm, mmap: do not blow on PROT_NONE MAP_FIXED holes in the stack
Date	2017-07-06 08:50 +0200
Message-ID	<u08LT-OV-7@gated-at.bofh.it> (permalink)
References	<tZVOF-nA-3@gated-at.bofh.it> <tZWB4-Ve-19@gated-at.bofh.it> <tZXdM-1mP-15@gated-at.bofh.it> <tZZSh-3hk-5@gated-at.bofh.it>
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On Wed 05-07-17 14:18:49, Andrew Morton wrote:
> On Wed, 5 Jul 2017 20:28:49 +0200 Michal Hocko <mhocko@kernel.org> wrote:
> 
> > "mm: enlarge stack guard gap" has introduced a regression in some rust
> > and Java environments which are trying to implement their own stack
> > guard page.  They are punching a new MAP_FIXED mapping inside the
> > existing stack Vma.
> > 
> > This will confuse expand_{downwards,upwards} into thinking that the stack
> > expansion would in fact get us too close to an existing non-stack vma
> > which is a correct behavior wrt. safety. It is a real regression on
> > the other hand. Let's work around the problem by considering PROT_NONE
> > mapping as a part of the stack. This is a gros hack but overflowing to
> > such a mapping would trap anyway an we only can hope that usespace
> > knows what it is doing and handle it propely.
> > 
> > Fixes: d4d2d35e6ef9 ("mm: larger stack guard gap, between vmas")
> 
> That should be 1be7107fbe18, yes?

yes. d4d2d35e6ef9 was a cherry-pick into the mmotm git tree. Sorry about
that.

> > Debugged-by: Vlastimil Babka <vbabka@suse.cz>
> > Signed-off-by: Michal Hocko <mhocko@suse.com>

-- 
Michal Hocko
SUSE Labs

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[PATCH] mm: mm, mmap: do not blow on PROT_NONE MAP_FIXED holes in the stack Michal Hocko <mhocko@kernel.org> - 2017-07-05 19:00 +0200
  Re: [PATCH] mm: mm, mmap: do not blow on PROT_NONE MAP_FIXED holes in  the stack Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-05 19:50 +0200
    Re: [PATCH] mm: mm, mmap: do not blow on PROT_NONE MAP_FIXED holes  in the stack Michal Hocko <mhocko@kernel.org> - 2017-07-05 20:30 +0200
      Re: [PATCH] mm: mm, mmap: do not blow on PROT_NONE MAP_FIXED holes in  the stack Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-05 20:40 +0200
        Re: [PATCH] mm: mm, mmap: do not blow on PROT_NONE MAP_FIXED holes  in the stack Michal Hocko <mhocko@kernel.org> - 2017-07-05 21:00 +0200
          Re: [PATCH] mm: mm, mmap: do not blow on PROT_NONE MAP_FIXED holes in  the stack Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-05 21:20 +0200
            Re: [PATCH] mm: mm, mmap: do not blow on PROT_NONE MAP_FIXED holes  in the stack Willy Tarreau <w@1wt.eu> - 2017-07-05 21:20 +0200
          Re: [PATCH] mm: mm, mmap: do not blow on PROT_NONE MAP_FIXED holes  in the stack Michal Hocko <mhocko@kernel.org> - 2017-07-05 21:20 +0200
      Re: [PATCH] mm: mm, mmap: do not blow on PROT_NONE MAP_FIXED holes  in the stack Andrew Morton <akpm@linux-foundation.org> - 2017-07-05 23:20 +0200
        Re: [PATCH] mm: mm, mmap: do not blow on PROT_NONE MAP_FIXED holes in  the stack Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-05 23:50 +0200
        Re: [PATCH] mm: mm, mmap: do not blow on PROT_NONE MAP_FIXED holes  in the stack Michal Hocko <mhocko@kernel.org> - 2017-07-06 08:50 +0200

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