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Re: [PATCH] mm: larger stack guard gap, between vmas

From Michal Hocko <mhocko@kernel.org>
Newsgroups linux.kernel
Subject Re: [PATCH] mm: larger stack guard gap, between vmas
Date 2017-07-05 08:40 +0200
Message-ID <tZM8F-2Dh-5@gated-at.bofh.it> (permalink)
References (5 earlier) <tZsD0-6u0-19@gated-at.bofh.it> <tZtz3-76W-9@gated-at.bofh.it> <tZuls-7Dd-23@gated-at.bofh.it> <tZF7c-6uZ-9@gated-at.bofh.it> <tZFAe-6E3-3@gated-at.bofh.it>
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On Tue 04-07-17 16:31:52, Linus Torvalds wrote:
> On Tue, Jul 4, 2017 at 4:01 PM, Ben Hutchings <ben@decadent.org.uk> wrote:
> >
> > We have:
> >
> > bottom = 0xff803fff
> > sp =     0xffffb178
> >
> > The relevant mappings are:
> >
> > ff7fc000-ff7fd000 rwxp 00000000 00:00 0
> > fffdd000-ffffe000 rw-p 00000000 00:00 0                                  [stack]
> 
> Ugh. So that stack is actually 8MB in size, but the alloca() is about
> to use up almost all of it, and there's only about 28kB left between
> "bottom" and that 'rwx' mapping.
> 
> Still, that rwx mapping is interesting: it is a single page, and it
> really is almost exactly 8MB below the stack.
> 
> In fact, the top of stack (at 0xffffe000) is *exactly* 8MB+4kB from
> the top of that odd one-page allocation (0xff7fd000).

Very interesting! I would be really curious whether changing ulimit to
something bigger changes the picture. And if this is really the case
what we are going to do here. We can special case a single page mapping
under the stack but that sounds quite dangerous for something that is
dubious in itself. PROT_NONE would explicitly fault but we would simply
run over this mapping too easily and who knows what might end up below
it. So to me the guard gap does its job here.

Do you want me to post the earier patch to ignore PROT_NONE mapping
or we should rather wait for this one to get more details?
-- 
Michal Hocko
SUSE Labs

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Re: [PATCH] mm: larger stack guard gap, between vmas Ben Hutchings <ben@decadent.org.uk> - 2017-07-04 02:00 +0200
  Re: [PATCH] mm: larger stack guard gap, between vmas Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-04 02:10 +0200
    Re: [PATCH] mm: larger stack guard gap, between vmas Michal Hocko <mhocko@kernel.org> - 2017-07-04 10:50 +0200
      Re: [PATCH] mm: larger stack guard gap, between vmas Michal Hocko <mhocko@kernel.org> - 2017-07-04 11:40 +0200
        Re: [PATCH] mm: larger stack guard gap, between vmas Willy Tarreau <w@1wt.eu> - 2017-07-04 11:50 +0200
          Re: [PATCH] mm: larger stack guard gap, between vmas Michal Hocko <mhocko@kernel.org> - 2017-07-04 12:50 +0200
            Re: [PATCH] mm: larger stack guard gap, between vmas Ben Hutchings <ben@decadent.org.uk> - 2017-07-04 13:40 +0200
              Re: [PATCH] mm: larger stack guard gap, between vmas Michal Hocko <mhocko@kernel.org> - 2017-07-04 14:10 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Michal Hocko <mhocko@kernel.org> - 2017-07-04 14:20 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Ben Hutchings <ben@decadent.org.uk> - 2017-07-04 14:30 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Michal Hocko <mhocko@kernel.org> - 2017-07-04 14:40 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Ximin Luo <infinity0@debian.org> - 2017-07-04 16:30 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Michal Hocko <mhocko@kernel.org> - 2017-07-04 16:50 +0200
              Re: [PATCH] mm: larger stack guard gap, between vmas Willy Tarreau <w@1wt.eu> - 2017-07-04 18:00 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Michal Hocko <mhocko@kernel.org> - 2017-07-04 19:30 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-04 20:40 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-04 20:50 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Willy Tarreau <w@1wt.eu> - 2017-07-04 21:10 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Willy Tarreau <w@1wt.eu> - 2017-07-04 20:50 +0200
              Re: [PATCH] mm: larger stack guard gap, between vmas Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-04 18:20 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas John Haxby <john.haxby@oracle.com> - 2017-07-04 18:30 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Willy Tarreau <w@1wt.eu> - 2017-07-04 19:10 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Ben Hutchings <ben@decadent.org.uk> - 2017-07-05 14:30 +0200
              Re: [PATCH] mm: larger stack guard gap, between vmas Willy Tarreau <w@1wt.eu> - 2017-07-04 19:20 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Ben Hutchings <ben@decadent.org.uk> - 2017-07-05 14:30 +0200
              Re: [PATCH] mm: larger stack guard gap, between vmas Ben Hutchings <ben@decadent.org.uk> - 2017-07-05 01:10 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-05 01:40 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Michal Hocko <mhocko@kernel.org> - 2017-07-05 08:40 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Willy Tarreau <w@1wt.eu> - 2017-07-05 10:20 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Michal Hocko <mhocko@kernel.org> - 2017-07-05 10:30 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Willy Tarreau <w@1wt.eu> - 2017-07-05 11:20 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Ben Hutchings <ben@decadent.org.uk> - 2017-07-05 14:30 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Willy Tarreau <w@1wt.eu> - 2017-07-05 16:00 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Michal Hocko <mhocko@kernel.org> - 2017-07-05 16:30 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-05 18:10 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Michal Hocko <mhocko@kernel.org> - 2017-07-06 09:40 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Ben Hutchings <ben@decadent.org.uk> - 2017-07-05 14:30 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Michal Hocko <mhocko@kernel.org> - 2017-07-05 16:30 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Ben Hutchings <ben@decadent.org.uk> - 2017-07-05 17:30 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Michal Hocko <mhocko@kernel.org> - 2017-07-05 18:10 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Ben Hutchings <ben@decadent.org.uk> - 2017-07-05 19:00 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Michal Hocko <mhocko@kernel.org> - 2017-07-05 19:10 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Ben Hutchings <ben@decadent.org.uk> - 2017-07-05 19:30 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-05 19:20 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Ben Hutchings <ben@decadent.org.uk> - 2017-07-06 01:40 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-06 02:00 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Willy Tarreau <w@1wt.eu> - 2017-07-06 10:30 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Willy Tarreau <w@1wt.eu> - 2017-07-06 12:20 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Andy Lutomirski <luto@kernel.org> - 2017-07-05 18:20 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-05 18:30 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Andy Lutomirski <luto@kernel.org> - 2017-07-05 19:30 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Ben Hutchings <ben@decadent.org.uk> - 2017-07-05 21:40 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Willy Tarreau <w@1wt.eu> - 2017-07-05 22:50 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Andy Lutomirski <luto@amacapital.net> - 2017-07-05 23:00 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Ben Hutchings <ben@decadent.org.uk> - 2017-07-06 02:00 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Andy Lutomirski <luto@kernel.org> - 2017-07-06 02:30 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Kees Cook <keescook@chromium.org> - 2017-07-06 02:00 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-06 02:00 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Andy Lutomirski <luto@kernel.org> - 2017-07-06 02:40 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-06 02:50 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Andy Lutomirski <luto@kernel.org> - 2017-07-06 02:30 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Kees Cook <keescook@chromium.org> - 2017-07-06 04:50 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Willy Tarreau <w@1wt.eu> - 2017-07-06 07:30 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Kevin Easton <kevin@guarana.org> - 2017-07-06 07:40 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-05 18:20 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Willy Tarreau <w@1wt.eu> - 2017-07-05 21:10 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Willy Tarreau <w@1wt.eu> - 2017-07-05 21:20 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-05 21:30 +0200
                Re: [PATCH] mm: larger stack guard gap, between vmas Linus Torvalds <torvalds@linux-foundation.org> - 2017-07-05 21:20 +0200
                Re: [vs-plain] Re: [PATCH] mm: larger stack guard gap, between vmas "kseifried@redhat.com" <kseifried@redhat.com> - 2017-07-05 03:20 +0200
                Re: [vs-plain] Re: [PATCH] mm: larger stack guard gap, between vmas Solar Designer <solar@openwall.com> - 2017-07-05 16:20 +0200
        Re: [PATCH] mm: larger stack guard gap, between vmas Michal Hocko <mhocko@kernel.org> - 2017-07-04 12:50 +0200
          Re: [PATCH] mm: larger stack guard gap, between vmas Michal Hocko <mhocko@kernel.org> - 2017-07-04 13:00 +0200
  Re: [PATCH] mm: larger stack guard gap, between vmas Andy Lutomirski <luto@kernel.org> - 2017-07-04 02:30 +0200
  Re: [vs-plain] Re: [PATCH] mm: larger stack guard gap, between vmas John Haxby <john.haxby@oracle.com> - 2017-07-04 14:30 +0200

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