Re: [PATCH v2] x86, mm: set NX across entire PMD at boot
From: Thomas Gleixner
Date: Tue Nov 18 2014 - 12:12:14 EST
On Fri, 14 Nov 2014, Kees Cook wrote:
> On Fri, Nov 14, 2014 at 6:29 PM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote:
> > On Fri, Nov 14, 2014 at 5:29 PM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote:
> >> On Fri, Nov 14, 2014 at 12:45 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> >>> v2:
> >>> - added call to free_init_pages(), as suggested by tglx
> >> something is wrong:
> >> [ 7.842479] Freeing unused kernel memory: 3844K (ffffffff82e52000 -
> >> ffffffff83213000)
> >> [ 7.843305] Write protecting the kernel read-only data: 28672k
> > ....
> > should use attached one instead.
> > 1. should use _brk_end instead of &end, as we only use partial of
> > brk.
> > 2. [_brk_end, pm_end) page range is already converted. aka
> > is not wasted.
> Are you sure? For me, _brk_end isn't far enough:
_brk_end is guaranteed to be <= _end. But we really want to use
_brk_end here, because if we have the following situation:
So we have the following PMDs setup:
0x03e00000 pmd rw nx <- covers the top of .bss
and the start of .brk
0x04000000 pmd rw nx <- covers the end of .brk
and some random unused
So if _brk_end is less than 0x04000000, then cleanup_highmem() has
zapped the extra PMD already. So we don't want to call set_nx() on
If _brk_end is >= 0x04000000 then we cover that last pmd with the
Completely non obvious as anything else in that area.
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