From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935907AbdADMRl (ORCPT ); Wed, 4 Jan 2017 07:17:41 -0500 Received: from foss.arm.com ([217.140.101.70]:49434 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935124AbdADMRi (ORCPT ); Wed, 4 Jan 2017 07:17:38 -0500 Date: Wed, 4 Jan 2017 12:16:41 +0000 From: Will Deacon To: Ard Biesheuvel Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, catalin.marinas@arm.com, akpm@linux-foundation.org, hanjun.guo@linaro.org, xieyisheng1@huawei.com, rrichter@cavium.com, james.morse@arm.com Subject: Re: [PATCH 1/2] mm: don't dereference struct page fields of invalid pages Message-ID: <20170104121641.GC18193@arm.com> References: <1481706707-6211-1-git-send-email-ard.biesheuvel@linaro.org> <1481706707-6211-2-git-send-email-ard.biesheuvel@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1481706707-6211-2-git-send-email-ard.biesheuvel@linaro.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 14, 2016 at 09:11:46AM +0000, Ard Biesheuvel wrote: > The VM_BUG_ON() check in move_freepages() checks whether the node > id of a page matches the node id of its zone. However, it does this > before having checked whether the struct page pointer refers to a > valid struct page to begin with. This is guaranteed in most cases, > but may not be the case if CONFIG_HOLES_IN_ZONE=y. > > So reorder the VM_BUG_ON() with the pfn_valid_within() check. > > Signed-off-by: Ard Biesheuvel > --- > mm/page_alloc.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index f64e7bcb43b7..4e298e31fa86 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1864,14 +1864,14 @@ int move_freepages(struct zone *zone, > #endif > > for (page = start_page; page <= end_page;) { > - /* Make sure we are not inadvertently changing nodes */ > - VM_BUG_ON_PAGE(page_to_nid(page) != zone_to_nid(zone), page); > - > if (!pfn_valid_within(page_to_pfn(page))) { > page++; > continue; > } > > + /* Make sure we are not inadvertently changing nodes */ > + VM_BUG_ON_PAGE(page_to_nid(page) != zone_to_nid(zone), page); > + > if (!PageBuddy(page)) { > page++; > continue; Acked-by: Will Deacon I'm guessing akpm can pick this up as a non-urgent fix. Will