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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 CF0EAC433E6 for ; Thu, 11 Mar 2021 15:01:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8A2DF64F98 for ; Thu, 11 Mar 2021 15:01:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233973AbhCKPAu (ORCPT ); Thu, 11 Mar 2021 10:00:50 -0500 Received: from foss.arm.com ([217.140.110.172]:37944 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233765AbhCKPAb (ORCPT ); Thu, 11 Mar 2021 10:00:31 -0500 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 4321C1FB; Thu, 11 Mar 2021 07:00:31 -0800 (PST) Received: from [10.37.8.5] (unknown [10.37.8.5]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 54F7F3F70D; Thu, 11 Mar 2021 07:00:28 -0800 (PST) Subject: Re: [PATCH v14 8/8] kselftest/arm64: Verify that TCO is enabled in load_unaligned_zeropad() To: Catalin Marinas Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, Andrew Morton , Will Deacon , Dmitry Vyukov , Andrey Ryabinin , Alexander Potapenko , Marco Elver , Evgenii Stepanov , Branislav Rankov , Andrey Konovalov , Lorenzo Pieralisi References: <20210308161434.33424-1-vincenzo.frascino@arm.com> <20210308161434.33424-9-vincenzo.frascino@arm.com> <20210311132509.GB30821@arm.com> From: Vincenzo Frascino Message-ID: Date: Thu, 11 Mar 2021 15:00:26 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210311132509.GB30821@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/11/21 1:25 PM, Catalin Marinas wrote: > On Mon, Mar 08, 2021 at 04:14:34PM +0000, Vincenzo Frascino wrote: >> load_unaligned_zeropad() and __get/put_kernel_nofault() functions can >> read passed some buffer limits which may include some MTE granule with a >> different tag. >> >> When MTE async mode is enable, the load operation crosses the boundaries >> and the next granule has a different tag the PE sets the TFSR_EL1.TF1 >> bit as if an asynchronous tag fault is happened: >> >> ================================================================== >> BUG: KASAN: invalid-access >> Asynchronous mode enabled: no access details available >> >> CPU: 0 PID: 1 Comm: init Not tainted 5.12.0-rc1-ge1045c86620d-dirty #8 >> Hardware name: FVP Base RevC (DT) >> Call trace: >> dump_backtrace+0x0/0x1c0 >> show_stack+0x18/0x24 >> dump_stack+0xcc/0x14c >> kasan_report_async+0x54/0x70 >> mte_check_tfsr_el1+0x48/0x4c >> exit_to_user_mode+0x18/0x38 >> finish_ret_to_user+0x4/0x15c >> ================================================================== >> >> Verify that Tag Check Override (TCO) is enabled in these functions before >> the load and disable it afterwards to prevent this to happen. >> >> Note: The issue has been observed only with an MTE enabled userspace. > > The above bug is all about kernel buffers. While userspace can trigger > the relevant code paths, it should not matter whether the user has MTE > enabled or not. Can you please confirm that you can still triggered the > fault with kernel-mode MTE but non-MTE user-space? If not, we may have a > bug somewhere as the two are unrelated: load_unaligned_zeropad() only > acts on kernel buffers and are subject to the kernel MTE tag check fault > mode. > I retried and you are right, it does not matter if it is a MTE or non-MTE user-space. The issue seems to be that this test does not trigger the problem all the times which probably lead me to the wrong conclusions. > I don't think we should have a user-space selftest for this. The bug is > not about a user-kernel interface, so an in-kernel test is more > appropriate. Could we instead add this to the kasan tests and calling > load_unaligned_zeropad() and other functions directly? > I agree with you we should abandon this strategy of triggering the issue due to my comment above. I will investigate the option of having a kasan test and try to come up with one that calls the relevant functions directly. I would prefer though, since the rest of the series is almost ready, to post it in a future series. What do you think? -- Regards, Vincenzo