From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, USER_AGENT_SANE_2 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C7099C3A5A0 for ; Mon, 19 Aug 2019 14:22:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9BADD20651 for ; Mon, 19 Aug 2019 14:22:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726769AbfHSOWF (ORCPT ); Mon, 19 Aug 2019 10:22:05 -0400 Received: from mailgw01.mediatek.com ([210.61.82.183]:6772 "EHLO mailgw01.mediatek.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1726028AbfHSOWF (ORCPT ); Mon, 19 Aug 2019 10:22:05 -0400 X-UUID: 8c89e3d18e8d4292afa7d8bd1e6b4842-20190819 X-UUID: 8c89e3d18e8d4292afa7d8bd1e6b4842-20190819 Received: from mtkcas08.mediatek.inc [(172.21.101.126)] by mailgw01.mediatek.com (envelope-from ) (Cellopoint E-mail Firewall v4.1.10 Build 0707 with TLS) with ESMTP id 42098201; Mon, 19 Aug 2019 22:21:54 +0800 Received: from MTKCAS06.mediatek.inc (172.21.101.30) by mtkmbs07n1.mediatek.inc (172.21.101.16) with Microsoft SMTP Server (TLS) id 15.0.1395.4; Mon, 19 Aug 2019 22:21:56 +0800 Received: from [172.21.84.99] (172.21.84.99) by MTKCAS06.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.0.1395.4 via Frontend Transport; Mon, 19 Aug 2019 22:21:56 +0800 Message-ID: <1566224517.9993.6.camel@mtksdccf07> Subject: Re: [PATCH] arm64: kasan: fix phys_to_virt() false positive on tag-based kasan From: Walter Wu To: Andrey Ryabinin CC: Will Deacon , Mark Rutland , Alexander Potapenko , Dmitry Vyukov , Catalin Marinas , "Will Deacon" , Matthias Brugger , Andrew Morton , Andrey Konovalov , , , , , Date: Mon, 19 Aug 2019 22:21:57 +0800 In-Reply-To: <8df7ec20-2fd2-8076-9a34-ac4c9785e91a@virtuozzo.com> References: <20190819114420.2535-1-walter-zh.wu@mediatek.com> <20190819125625.bu3nbrldg7te5kwc@willie-the-truck> <20190819132347.GB9927@lakrids.cambridge.arm.com> <20190819133441.ejomv6cprdcz7hh6@willie-the-truck> <8df7ec20-2fd2-8076-9a34-ac4c9785e91a@virtuozzo.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit MIME-Version: 1.0 X-MTK: N Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2019-08-19 at 17:06 +0300, Andrey Ryabinin wrote: > > On 8/19/19 4:34 PM, Will Deacon wrote: > > On Mon, Aug 19, 2019 at 02:23:48PM +0100, Mark Rutland wrote: > >> On Mon, Aug 19, 2019 at 01:56:26PM +0100, Will Deacon wrote: > >>> On Mon, Aug 19, 2019 at 07:44:20PM +0800, Walter Wu wrote: > >>>> __arm_v7s_unmap() call iopte_deref() to translate pyh_to_virt address, > >>>> but it will modify pointer tag into 0xff, so there is a false positive. > >>>> > >>>> When enable tag-based kasan, phys_to_virt() function need to rewrite > >>>> its original pointer tag in order to avoid kasan report an incorrect > >>>> memory corruption. > >>> > >>> Hmm. Which tree did you see this on? We've recently queued a load of fixes > >>> in this area, but I /thought/ they were only needed after the support for > >>> 52-bit virtual addressing in the kernel. > >> > >> I'm seeing similar issues in the virtio blk code (splat below), atop of > >> the arm64 for-next/core branch. I think this is a latent issue, and > >> people are only just starting to test with KASAN_SW_TAGS. > >> > >> It looks like the virtio blk code will round-trip a SLUB-allocated pointer from > >> virt->page->virt, losing the per-object tag in the process. > >> > >> Our page_to_virt() seems to get a per-page tag, but this only makes > >> sense if you're dealing with the page allocator, rather than something > >> like SLUB which carves a page into smaller objects giving each object a > >> distinct tag. > >> > >> Any round-trip of a pointer from SLUB is going to lose the per-object > >> tag. > > > > Urgh, I wonder how this is supposed to work? > > > > We supposed to ignore pointers with 0xff tags. We do ignore them when memory access checked, > but not in kfree() path. > This untested patch should fix the issue: > > > > --- > mm/kasan/common.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/kasan/common.c b/mm/kasan/common.c > index 895dc5e2b3d5..0a81cc328049 100644 > --- a/mm/kasan/common.c > +++ b/mm/kasan/common.c > @@ -407,7 +407,7 @@ static inline bool shadow_invalid(u8 tag, s8 shadow_byte) > return shadow_byte < 0 || > shadow_byte >= KASAN_SHADOW_SCALE_SIZE; > else > - return tag != (u8)shadow_byte; > + return (tag != KASAN_TAG_KERNEL) && (tag != (u8)shadow_byte); > } > > static bool __kasan_slab_free(struct kmem_cache *cache, void *object, Hi, Andrey, Does it miss the double-free case after ignore pointer tag 0xff ? and please help review my another patch about memory corruption identification. Thanks your respondence Walter