Re: rwx mapping between ex_table and rodata

From	Thomas Gleixner <tglx@linutronix.de>
Newsgroups	linux.kernel
Subject	Re: rwx mapping between ex_table and rodata
Date	2015-10-01 11:10 +0200
Message-ID	<qeI2d-7Z7-1@gated-at.bofh.it> (permalink)
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On Mon, 28 Sep 2015, Kees Cook wrote:
> > --- a/arch/x86/mm/init_64.c
> > +++ b/arch/x86/mm/init_64.c
> > @@ -1132,7 +1132,7 @@ void mark_rodata_ro(void)
> >          * has been zapped already via cleanup_highmem().
> >          */
> >         all_end = roundup((unsigned long)_brk_end, PMD_SIZE);
> > -       set_memory_nx(rodata_start, (all_end - rodata_start) >> PAGE_SHIFT);
> > +       set_memory_nx(text_end, (all_end - text_end) >> PAGE_SHIFT);
> >
> >         rodata_test();
> >
> >
> 
> That should work, yeah. I'd still like to find the default permissions
> and make them W+nx, though. Regardless, let's get the above added.

The default permissions are set at boot time when setting up the early
page tables. When we split them up later on we inherit the PTE bits
and then we do that _ro/nx cleanup after the overall layout has been
settled.

We can't make them W+nx in the early setup without shooting ourself in
the foot, because we only set up at the pud/pmd level.

Thanks,

	tglx


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Thread

Re: rwx mapping between ex_table and rodata Kees Cook <keescook@chromium.org> - 2015-09-25 00:30 +0200
  Re: rwx mapping between ex_table and rodata Ingo Molnar <mingo@kernel.org> - 2015-09-25 09:30 +0200
  Re: rwx mapping between ex_table and rodata Ingo Molnar <mingo@kernel.org> - 2015-09-25 09:30 +0200
    Re: rwx mapping between ex_table and rodata Kees Cook <keescook@chromium.org> - 2015-09-26 18:50 +0200
    Re: rwx mapping between ex_table and rodata "H. Peter Anvin" <hpa@zytor.com> - 2015-09-28 23:20 +0200
      Re: rwx mapping between ex_table and rodata Kees Cook <keescook@chromium.org> - 2015-09-29 00:10 +0200
        Re: rwx mapping between ex_table and rodata "H. Peter Anvin" <hpa@zytor.com> - 2015-09-29 00:30 +0200
  Re: rwx mapping between ex_table and rodata Stephen Smalley <sds@tycho.nsa.gov> - 2015-09-28 16:20 +0200
    Re: rwx mapping between ex_table and rodata Kees Cook <keescook@chromium.org> - 2015-09-28 20:30 +0200
      Re: rwx mapping between ex_table and rodata Ingo Molnar <mingo@kernel.org> - 2015-10-01 09:20 +0200
      Re: rwx mapping between ex_table and rodata Thomas Gleixner <tglx@linutronix.de> - 2015-10-01 11:10 +0200
        Re: rwx mapping between ex_table and rodata Ingo Molnar <mingo@kernel.org> - 2015-10-01 11:20 +0200
          Re: rwx mapping between ex_table and rodata Kees Cook <keescook@chromium.org> - 2015-10-01 19:50 +0200
            Re: rwx mapping between ex_table and rodata Ingo Molnar <mingo@kernel.org> - 2015-10-02 09:20 +0200

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