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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 05234C433E6 for ; Fri, 12 Mar 2021 13:50:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BACDB64F9E for ; Fri, 12 Mar 2021 13:50:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231496AbhCLNuP (ORCPT ); Fri, 12 Mar 2021 08:50:15 -0500 Received: from imap3.hz.codethink.co.uk ([176.9.8.87]:44926 "EHLO imap3.hz.codethink.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229995AbhCLNuK (ORCPT ); Fri, 12 Mar 2021 08:50:10 -0500 Received: from cpc79921-stkp12-2-0-cust288.10-2.cable.virginm.net ([86.16.139.33] helo=[192.168.0.18]) by imap3.hz.codethink.co.uk with esmtpsa (Exim 4.92 #3 (Debian)) id 1lKiAt-0008V6-CR; Fri, 12 Mar 2021 13:49:55 +0000 Subject: Re: [syzbot] BUG: unable to handle kernel access to user memory in schedule_tail To: Dmitry Vyukov , syzbot , Paul Walmsley , Palmer Dabbelt , Albert Ou , linux-riscv Cc: Daniel Bristot de Oliveira , Benjamin Segall , dietmar.eggemann@arm.com, Juri Lelli , LKML , Mel Gorman , Ingo Molnar , Peter Zijlstra , Steven Rostedt , syzkaller-bugs , Vincent Guittot References: <000000000000b74f1b05bd316729@google.com> From: Ben Dooks Organization: Codethink Limited. Message-ID: <84b0471d-42c1-175f-ae1d-a18c310c7f77@codethink.co.uk> Date: Fri, 12 Mar 2021 13:49:53 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/03/2021 17:16, Dmitry Vyukov wrote: > On Wed, Mar 10, 2021 at 5:46 PM syzbot > wrote: >> >> Hello, >> >> syzbot found the following issue on: >> >> HEAD commit: 0d7588ab riscv: process: Fix no prototype for arch_dup_tas.. >> git tree: git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git fixes >> console output: https://syzkaller.appspot.com/x/log.txt?x=1212c6e6d00000 >> kernel config: https://syzkaller.appspot.com/x/.config?x=e3c595255fb2d136 >> dashboard link: https://syzkaller.appspot.com/bug?extid=e74b94fe601ab9552d69 >> userspace arch: riscv64 >> >> Unfortunately, I don't have any reproducer for this issue yet. >> >> IMPORTANT: if you fix the issue, please add the following tag to the commit: >> Reported-by: syzbot+e74b94fe601ab9552d69@syzkaller.appspotmail.com > > +riscv maintainers > > This is riscv64-specific. > I've seen similar crashes in put_user in other places. It looks like > put_user crashes in the user address is not mapped/protected (?). I've been having a look, and this seems to be down to access of the tsk->set_child_tid variable. I assume the fuzzing here is to pass a bad address to clone? From looking at the code, the put_user() code should have set the relevant SR_SUM bit (the value for this, which is 1<<18 is in the s2 register in the crash report) and from looking at the compiler output from my gcc-10, the code looks to be dong the relevant csrs and then csrc around the put_user So currently I do not understand how the above could have happened over than something re-tried the code seqeunce and ended up retrying the faulting instruction without the SR_SUM bit set. -- Ben Dooks http://www.codethink.co.uk/ Senior Engineer Codethink - Providing Genius https://www.codethink.co.uk/privacy.html