From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f72.google.com (mail-wm0-f72.google.com [74.125.82.72]) by kanga.kvack.org (Postfix) with ESMTP id B34B76B025F for ; Mon, 7 Aug 2017 10:14:10 -0400 (EDT) Received: by mail-wm0-f72.google.com with SMTP id i187so1138663wma.15 for ; Mon, 07 Aug 2017 07:14:10 -0700 (PDT) Received: from lhrrgout.huawei.com (lhrrgout.huawei.com. [194.213.3.17]) by mx.google.com with ESMTPS id u107si8545488wrc.554.2017.08.07.07.14.09 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 07 Aug 2017 07:14:09 -0700 (PDT) Subject: Re: [RFC] Tagging of vmalloc pages for supporting the pmalloc allocator References: <8e82639c-40db-02ce-096a-d114b0436d3c@huawei.com> <20170803114844.GO12521@dhcp22.suse.cz> <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> From: Igor Stoppa Message-ID: <555dc453-3028-199a-881a-3ddeb41e4d6d@huawei.com> Date: Mon, 7 Aug 2017 17:13:00 +0300 MIME-Version: 1.0 In-Reply-To: <20170807133107.GA16616@redhat.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Jerome Glisse Cc: Michal Hocko , Linux-MM , LKML , linux-security-module@vger.kernel.org, "kernel-hardening@lists.openwall.com" , Kees Cook 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. -- igor -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org