Re: rwx mapping between ex_table and rodata

From	Ingo Molnar <mingo@kernel.org>
Newsgroups	linux.kernel
Subject	Re: rwx mapping between ex_table and rodata
Date	2015-10-01 11:20 +0200
Message-ID	<qeIbU-8aj-9@gated-at.bofh.it> (permalink)
References	(1 earlier) <qclCO-5zE-9@gated-at.bofh.it> <qcnbz-7Zv-11@gated-at.bofh.it> <qdHrA-1Q9-15@gated-at.bofh.it> <qdLlw-7nn-3@gated-at.bofh.it> <qeI2d-7Z7-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

* Thomas Gleixner <tglx@linutronix.de> wrote:

> 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.

So I think at minimum we should do a (debug) scan in late init, of the whole 
range, for any leftover WX permissions? That would have caught this bug. (and 
might catch other existing bugs that might occur with various configs/hw-layouts.)

Thanks,

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

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

csiph-web