Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751435AbcCKKFO (ORCPT ); Fri, 11 Mar 2016 05:05:14 -0500 Received: from mail-wm0-f54.google.com ([74.125.82.54]:36464 "EHLO mail-wm0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750937AbcCKKFG convert rfc822-to-8bit (ORCPT ); Fri, 11 Mar 2016 05:05:06 -0500 MIME-Version: 1.0 In-Reply-To: <20160310121426.b667420195a19ee17503ae2d@linux-foundation.org> References: <20160309122148.1250854b862349399591dabf@linux-foundation.org> <20160310121426.b667420195a19ee17503ae2d@linux-foundation.org> Date: Fri, 11 Mar 2016 11:05:05 +0100 Message-ID: Subject: Re: [PATCH v5 7/7] mm: kasan: Initial memory quarantine implementation From: Alexander Potapenko To: Andrew Morton Cc: Andrey Konovalov , Christoph Lameter , Dmitriy Vyukov , Andrey Ryabinin , Steven Rostedt , Joonsoo Kim , JoonSoo Kim , Kostya Serebryany , kasan-dev , LKML , Linux Memory Management List Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3733 Lines: 84 On Thu, Mar 10, 2016 at 9:14 PM, Andrew Morton wrote: > On Thu, 10 Mar 2016 14:50:56 +0100 Alexander Potapenko wrote: > >> On Wed, Mar 9, 2016 at 9:21 PM, Andrew Morton wrote: >> > On Wed, 9 Mar 2016 12:05:48 +0100 Alexander Potapenko wrote: >> > >> >> Quarantine isolates freed objects in a separate queue. The objects are >> >> returned to the allocator later, which helps to detect use-after-free >> >> errors. >> > >> > I'd like to see some more details on precisely *how* the parking of >> > objects in the qlists helps "detect use-after-free"? >> When the object is freed, its state changes from KASAN_STATE_ALLOC to >> KASAN_STATE_QUARANTINE. The object is poisoned and put into quarantine >> instead of being returned to the allocator, therefore every subsequent >> access to that object triggers a KASAN error, and the error handler is >> able to say where the object has been allocated and deallocated. >> When it's time for the object to leave quarantine, its state becomes >> KASAN_STATE_FREE and it's returned to the allocator. From now on the >> allocator may reuse it for another allocation. >> Before that happens, it's still possible to detect a use-after free on >> that object (it retains the allocation/deallocation stacks). >> When the allocator reuses this object, the shadow is unpoisoned and >> old allocation/deallocation stacks are wiped. Therefore a use of this >> object, even an incorrect one, won't trigger ASan warning. >> Without the quarantine, it's not guaranteed that the objects aren't >> reused immediately, that's why the probability of catching a >> use-after-free is lower than with quarantine in place. > > I see, thanks. I'll slurp that into the changelog for posterity. I've also added a paragraph about that to the patch description. >> >> +} >> > >> > We could avoid th4ese ifdefs in the usual way: an empty version of >> > quarantine_remove_cache() if CONFIG_SLAB=n. >> Yes, agreed. >> I am sorry, I don't fully understand the review process now, when >> you've pulled the patches into mm-tree. >> Shall I send the new patch series version, as before, or is anything >> else needs to be done? >> Do I need to rebase against mm- or linux-next? Thanks in advance. > > I like to queue a delta patch so I and others can see what changed and > also to keep track of who fixed what and why. It's a bit harsh on the > reviewers to send them a slightly altered version of a 500 line patch > which they've already read through. I'm listing the differences between patch versions after the patch description (between the triple dashes), hope that helps the reviewers. > Before sending the patch up to Linus I'll clump everything into a > single patch and a lot of that history is somewhat lost. > > Sending a replacement patch is often more convenient for the originator > so that's fine - I'll turn the replacement into a delta locally and > will review then queue that delta. Also a new revision of a patch has > an altered changelog so I'll manually move that into the older original > patch's changelog immediately. > > IOW: either a new patch or a delta is fine. Ok, got it. > Your patch is in linux-next now so a diff against -next will work OK. > > Probably the easiest thing for you to do is to just alter the patch you > have in-place and send out the new one. A "[v2" in the Subject: helps > people keep track of things. Ok, will do. -- Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Straße, 33 80636 München Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg