From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751982AbdHGTMm (ORCPT ); Mon, 7 Aug 2017 15:12:42 -0400 Received: from mx1.redhat.com ([209.132.183.28]:25289 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751761AbdHGTMj (ORCPT ); Mon, 7 Aug 2017 15:12:39 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com BE59FC047B7F Authentication-Results: ext-mx07.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx07.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=jglisse@redhat.com Date: Mon, 7 Aug 2017 15:12:36 -0400 From: Jerome Glisse To: Igor Stoppa Cc: Michal Hocko , Linux-MM , LKML , linux-security-module@vger.kernel.org, "kernel-hardening@lists.openwall.com" , Kees Cook Subject: Re: [RFC] Tagging of vmalloc pages for supporting the pmalloc allocator Message-ID: <20170807191235.GE16616@redhat.com> References: <20170803135549.GW12521@dhcp22.suse.cz> <20170803144746.GA9501@redhat.com> <20170803151550.GX12521@dhcp22.suse.cz> <20170804081240.GF26029@dhcp22.suse.cz> <7733852a-67c9-17a3-4031-cb08520b9ad2@huawei.com> <20170807133107.GA16616@redhat.com> <555dc453-3028-199a-881a-3ddeb41e4d6d@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <555dc453-3028-199a-881a-3ddeb41e4d6d@huawei.com> User-Agent: Mutt/1.8.3 (2017-05-23) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Mon, 07 Aug 2017 19:12:39 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 07, 2017 at 05:13:00PM +0300, Igor Stoppa wrote: > > > On 07/08/17 16:31, Jerome Glisse wrote: > > On Mon, Aug 07, 2017 at 02:26:21PM +0300, Igor Stoppa wrote: > > [...] > > >> I'll add a vm_area field as you advised. > >> > >> Is this something I could send as standalone patch? > > > > Note that vmalloc() is not the only thing that use vmalloc address > > space. There is also vmap() and i know one set of drivers that use > > vmap() and also use the mapping field of struct page namely GPU > > drivers. > > Ah, yes, you mentioned this. > > > So like i said previously i would store a flag inside vm_struct to > > know if page you are looking at are pmalloc or not. > > And I was planning to follow your advice, using one of the flags. > But ... > > > Again do you > > need to store something per page ? Would storing it per vm_struct > > not be enough ? > > ... there was this further comment, about speeding up the access to > vm_area, which seemed good from performance perspective. > > ---8<--------------8<--------------8<--------------8<--------------8<--- > 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 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. > ---8<--------------8<--------------8<--------------8<--------------8<--- > > I do not strictly need to modify the page struct, but it seems it might > harm performance, if it is added on the path of hardened usercopy. > > I have an updated version of the old proposal: > > * put a magic number in the private field, during initialization of > pmalloc pages > > * during hardened usercopy verification, when I have to assess if a page > is of pmalloc type, compare the private field against the magic number > > * if and only if the private field matches the magic number, then invoke > find_vm_area(), so that the slowness affects only a possibly limited > amount of false positives. This all sounds good to me. Jérôme