From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751685AbdHCOmz (ORCPT ); Thu, 3 Aug 2017 10:42:55 -0400 Received: from lhrrgout.huawei.com ([194.213.3.17]:32616 "EHLO lhrrgout.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751083AbdHCOmy (ORCPT ); Thu, 3 Aug 2017 10:42:54 -0400 Subject: Re: [RFC] Tagging of vmalloc pages for supporting the pmalloc allocator To: Michal Hocko CC: Jerome Glisse , Linux-MM , LKML , , "kernel-hardening@lists.openwall.com" , Kees Cook References: <07063abd-2f5d-20d9-a182-8ae9ead26c3c@huawei.com> <20170802170848.GA3240@redhat.com> <8e82639c-40db-02ce-096a-d114b0436d3c@huawei.com> <20170803114844.GO12521@dhcp22.suse.cz> <20170803135549.GW12521@dhcp22.suse.cz> From: Igor Stoppa Message-ID: <836b82ae-0d01-af73-d6fd-00343bb2a5b7@huawei.com> Date: Thu, 3 Aug 2017 17:41:24 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <20170803135549.GW12521@dhcp22.suse.cz> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.122.225.51] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A090204.59833654.0124,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2013-06-18 04:22:30, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: 5acb2892ebed374a65cb7f75df5c6bb5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/08/17 16:55, Michal Hocko wrote: > On Thu 03-08-17 15:20:31, Igor Stoppa wrote: >> On 03/08/17 14:48, Michal Hocko wrote: >>> On Thu 03-08-17 13:11:45, Igor Stoppa wrote: [...] >>>> But, to reply more specifically to your advice, yes, I think I could add >>>> a flag to vm_struct and then retrieve its value, for the address being >>>> processed, by passing through find_vm_area(). >>> >>> ... and you can store vm_struct pointer to the struct page there >> >> "there" as in the new field of the union? >> btw, what would be a meaningful name, since "private" is already taken? >> >> For simplicity, I'll use, for now, "private2" > > why not explicit vm_area? ok :-) >>> and you won't need to do the slow find_vm_area. I haven't checked >> very closely >>> but this should be possible in principle. I guess other callers might >>> benefit from this as well. >> >> I am confused about this: if "private2" is a pointer, but when I get an >> address, I do not even know if the address represents a valid pmalloc >> page, how can i know when it's ok to dereference "private2"? > > because you can make all pages which back vmalloc mappings have vm_area > pointer set. Ah, now I see, I had missed that the field would be set for *all* pages backed by vmalloc. So, given a pointer, I still have to figure out if it refers to a vmalloc area or not. However, that is something I need to do anyway, to get the reference to the corresponding page struct, in case it is indeed a vmalloc address. -- thanks, igor