Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core)

From	Andy Lutomirski <luto@amacapital.net>
Newsgroups	linux.kernel
Subject	Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core)
Date	2016-06-21 19:40 +0200
Message-ID	<rMxOx-pg-1@gated-at.bofh.it> (permalink)
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On Tue, Jun 21, 2016 at 10:16 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Tue, Jun 21, 2016 at 9:45 AM, Andy Lutomirski <luto@amacapital.net> wrote:
>>
>> So I'm leaning toward fewer cache entries per cpu, maybe just one.
>> I'm all for making it a bit faster, but I think we should weigh that
>> against increasing memory usage too much and thus scaring away the
>> embedded folks.
>
> I don't think the embedded folks will be scared by a per-cpu cache, if
> it's just one or two entries.  And I really do think that even just
> one or two entries will indeed catch a lot of the cases.
>
> And yes, fork+execve() is too damn expensive in page table build-up
> and tear-down. I'm not sure why bash doesn't do vfork+exec for when it
> has to wait for the process anyway, but it doesn't seem to do that.
>

I don't know about bash, but glibc very recently fixed a long-standing
but in posix_spawn and started using clone() in a sensible manner for
this.

FWIW, it may be a while before this can be enabled in distro kernels.
There are some code paths (*cough* crypto users *cough*) that think
that calling sg_init_one with a stack address is a reasonable thing to
do, and it doesn't work with a vmalloced stack.  grsecurity works
around this by using a real lowmem higher-order stack, aliasing it
into vmalloc space, and arranging for virt_to_phys to backtrack the
alias, but eww.  I think I'd rather find and fix the bugs, assuming
they're straightforward.

--Andy

Thread

[PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Andy Lutomirski <luto@kernel.org> - 2016-06-21 01:50 +0200
  [PATCH v3 02/13] x86/cpa: In populate_pgd, don't set the pgd entry until it's populated Andy Lutomirski <luto@kernel.org> - 2016-06-21 01:50 +0200
  [PATCH v3 03/13] x86/mm: Remove kernel_unmap_pages_in_pgd() and efi_cleanup_page_tables() Andy Lutomirski <luto@kernel.org> - 2016-06-21 01:50 +0200
    Re: [PATCH v3 03/13] x86/mm: Remove kernel_unmap_pages_in_pgd() and  efi_cleanup_page_tables() Matt Fleming <matt@codeblueprint.co.uk> - 2016-06-21 12:20 +0200
  [PATCH v3 11/13] x86/dumpstack/64: Handle faults when printing the "Stack:" part of an OOPS Andy Lutomirski <luto@kernel.org> - 2016-06-21 01:50 +0200
  [PATCH v3 06/13] fork: Add generic vmalloced stack support Andy Lutomirski <luto@kernel.org> - 2016-06-21 01:50 +0200
    Re: [PATCH v3 06/13] fork: Add generic vmalloced stack support Jann Horn <jannh@google.com> - 2016-06-21 12:10 +0200
      Re: [PATCH v3 06/13] fork: Add generic vmalloced stack support Andy Lutomirski <luto@amacapital.net> - 2016-06-21 19:10 +0200
        Re: [PATCH v3 06/13] fork: Add generic vmalloced stack support Kees Cook <keescook@chromium.org> - 2016-06-21 19:20 +0200
          Re: [PATCH v3 06/13] fork: Add generic vmalloced stack support Andy Lutomirski <luto@amacapital.net> - 2016-06-21 19:40 +0200
          Re: [kernel-hardening] Re: [PATCH v3 06/13] fork: Add generic  vmalloced stack support Rik van Riel <riel@redhat.com> - 2016-06-21 20:50 +0200
            Re: [kernel-hardening] Re: [PATCH v3 06/13] fork: Add generic  vmalloced stack support Andy Lutomirski <luto@amacapital.net> - 2016-06-21 21:50 +0200
            Re: [kernel-hardening] Re: [PATCH v3 06/13] fork: Add generic vmalloced stack support Arnd Bergmann <arnd@arndb.de> - 2016-06-21 22:00 +0200
  [PATCH v3 04/13] mm: Track NR_KERNEL_STACK in KiB instead of number of stacks Andy Lutomirski <luto@kernel.org> - 2016-06-21 01:50 +0200
    Re: [PATCH v3 04/13] mm: Track NR_KERNEL_STACK in KiB instead of  number of stacks Michal Hocko <mhocko@kernel.org> - 2016-06-22 10:50 +0200
  [PATCH v3 07/13] x86/die: Don't try to recover from an OOPS on a non-default stack Andy Lutomirski <luto@kernel.org> - 2016-06-21 01:50 +0200
  [PATCH v3 08/13] x86/dumpstack: When OOPSing, rewind the stack before do_exit Andy Lutomirski <luto@kernel.org> - 2016-06-21 01:50 +0200
  [PATCH v3 01/13] x86/mm/hotplug: Don't remove PGD entries in remove_pagetable() Andy Lutomirski <luto@kernel.org> - 2016-06-21 01:50 +0200
  [PATCH v3 10/13] x86/dumpstack: Try harder to get a call trace on stack overflow Andy Lutomirski <luto@kernel.org> - 2016-06-21 01:50 +0200
  [PATCH v3 09/13] x86/dumpstack: When dumping stack bytes due to OOPS, start with regs->sp Andy Lutomirski <luto@kernel.org> - 2016-06-21 01:50 +0200
  Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Linus Torvalds <torvalds@linux-foundation.org> - 2016-06-21 06:10 +0200
    Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Andy Lutomirski <luto@amacapital.net> - 2016-06-21 18:50 +0200
      Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Linus Torvalds <torvalds@linux-foundation.org> - 2016-06-21 19:20 +0200
        Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Andy Lutomirski <luto@amacapital.net> - 2016-06-21 19:40 +0200
          Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Kees Cook <keescook@chromium.org> - 2016-06-21 20:20 +0200
            Re: [kernel-hardening] Re: [PATCH v3 00/13] Virtually mapped stacks  with guard pages (x86, core) Rik van Riel <riel@redhat.com> - 2016-06-21 20:30 +0200
    Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Andy Lutomirski <luto@amacapital.net> - 2016-06-23 03:30 +0200
      Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Linus Torvalds <torvalds@linux-foundation.org> - 2016-06-23 08:10 +0200
        Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86,  core) Oleg Nesterov <oleg@redhat.com> - 2016-06-23 16:40 +0200
          Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Linus Torvalds <torvalds@linux-foundation.org> - 2016-06-23 18:40 +0200
            Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Andy Lutomirski <luto@amacapital.net> - 2016-06-23 18:50 +0200
              Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86,  core) Oleg Nesterov <oleg@redhat.com> - 2016-06-23 19:20 +0200
            Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86,  core) Oleg Nesterov <oleg@redhat.com> - 2016-06-23 19:10 +0200
  Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Arnd Bergmann <arnd@arndb.de> - 2016-06-21 11:40 +0200
    Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Kees Cook <keescook@chromium.org> - 2016-06-21 19:30 +0200
      Re: [kernel-hardening] Re: [PATCH v3 00/13] Virtually mapped stacks  with guard pages (x86, core) Andy Lutomirski <luto@amacapital.net> - 2016-06-21 20:10 +0200
      Re: [kernel-hardening] Re: [PATCH v3 00/13] Virtually mapped stacks  with guard pages (x86, core) Rik van Riel <riel@redhat.com> - 2016-06-21 20:10 +0200
      Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Andy Lutomirski <luto@amacapital.net> - 2016-06-21 21:50 +0200
        Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Kees Cook <keescook@chromium.org> - 2016-06-21 22:20 +0200
      Re: [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Arnd Bergmann <arnd@arndb.de> - 2016-06-21 21:50 +0200

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