linux-kernel - Re: [PATCH v2] x86, mm: set NX across entire PMD at boot

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Date:	Sun, 16 Nov 2014 19:52:05 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Yinghai Lu <yinghai@...nel.org>
cc:	Kees Cook <keescook@...omium.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Wang Nan <wangnan0@...wei.com>,
	David Vrabel <david.vrabel@...rix.com>
Subject: Re: [PATCH v2] x86, mm: set NX across entire PMD at boot

On Fri, 14 Nov 2014, Yinghai Lu wrote:

> On Fri, Nov 14, 2014 at 6:46 PM, Kees Cook <keescook@...omium.org> wrote:
> > On Fri, Nov 14, 2014 at 6:29 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> 
> >> 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:
> >
> > [    1.475572] all_end: 0xffffffff82df5000
> > [    1.476736] _brk_end: 0xffffffff82dd6000
> 
> Yes. _brk_end should be small then &_end.

Wrong. _brk_end can move up to _end, i.e. to __brk_limit.
 
But it's safe to use _brk_end when mark_rodata_ro() is called because
extend_brk() is gone already at that point.

Thanks,

	tglx
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