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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 E782AC3A5A2 for ; Mon, 19 Aug 2019 14:35:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C623A20673 for ; Mon, 19 Aug 2019 14:35:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727086AbfHSOfV (ORCPT ); Mon, 19 Aug 2019 10:35:21 -0400 Received: from foss.arm.com ([217.140.110.172]:55622 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726464AbfHSOfU (ORCPT ); Mon, 19 Aug 2019 10:35:20 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A1DDB28; Mon, 19 Aug 2019 07:35:19 -0700 (PDT) Received: from [10.1.197.57] (e110467-lin.cambridge.arm.com [10.1.197.57]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AC6923F718; Mon, 19 Aug 2019 07:35:17 -0700 (PDT) Subject: Re: [PATCH] arm64: kasan: fix phys_to_virt() false positive on tag-based kasan To: Will Deacon , Andrey Konovalov Cc: Mark Rutland , Walter Wu , wsd_upstream@mediatek.com, Catalin Marinas , Will Deacon , LKML , kasan-dev , linux-mediatek@lists.infradead.org, Alexander Potapenko , Linux ARM , Matthias Brugger , Andrey Ryabinin , Andrew Morton , Dmitry Vyukov 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> <20190819142238.2jobs6vabkp2isg2@willie-the-truck> From: Robin Murphy Message-ID: <1ac7eb3e-156f-218c-8c5a-39a05dd46d55@arm.com> Date: Mon, 19 Aug 2019 15:35:16 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190819142238.2jobs6vabkp2isg2@willie-the-truck> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/08/2019 15:22, Will Deacon wrote: > On Mon, Aug 19, 2019 at 04:05:22PM +0200, Andrey Konovalov wrote: >> On Mon, Aug 19, 2019 at 3:34 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? >>> >>> If we end up having to check the KASAN shadow for *_to_virt(), then why >>> do we need to store anything in the page flags at all? Andrey? >> >> As per 2813b9c0 ("kasan, mm, arm64: tag non slab memory allocated via >> pagealloc") we should only save a non-0xff tag in page flags for non >> slab pages. > > Thanks, that makes sense. Hopefully the patch from Andrey R will solve > both of the reported splats, since I'd not realised they were both on the > kfree() path. > >> Could you share your .config so I can reproduce this? > > This is in the iopgtable code, so it's probably pretty tricky to trigger > at runtime unless you have the write IOMMU hardware, unfortunately. If simply freeing any entry from the l2_tables cache is sufficient, then the short-descriptor selftest should do the job, and that ought to run on anything (modulo insane RAM layouts). Robin.