Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754798AbaKRRMI (ORCPT ); Tue, 18 Nov 2014 12:12:08 -0500 Received: from www.linutronix.de ([62.245.132.108]:40417 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753833AbaKRRMF (ORCPT ); Tue, 18 Nov 2014 12:12:05 -0500 Date: Tue, 18 Nov 2014 18:11:57 +0100 (CET) From: Thomas Gleixner To: Kees Cook cc: Yinghai Lu , Linux Kernel Mailing List , Ingo Molnar , "H. Peter Anvin" , the arch/x86 maintainers , Andrew Morton , Andy Lutomirski , Yasuaki Ishimatsu , Wang Nan , David Vrabel Subject: Re: [PATCH v2] x86, mm: set NX across entire PMD at boot In-Reply-To: Message-ID: References: <20141114204517.GA24402@www.outflux.net> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 14 Nov 2014, Kees Cook wrote: > On Fri, Nov 14, 2014 at 6:29 PM, Yinghai Lu wrote: > > On Fri, Nov 14, 2014 at 5:29 PM, Yinghai Lu wrote: > >> On Fri, Nov 14, 2014 at 12:45 PM, Kees Cook 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: _brk_start: 0x03ff0000 _brk_end: 0x03ffff00 _end: 0x04016000 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 that. If _brk_end is >= 0x04000000 then we cover that last pmd with the set_nx call. Completely non obvious as anything else in that area. Thanks, tglx -- 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/