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[23.128.96.18]) by mx.google.com with ESMTP id j12si1118793edp.565.2021.03.10.22.41.50; Wed, 10 Mar 2021 22:42:12 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230526AbhCKGkQ (ORCPT + 99 others); Thu, 11 Mar 2021 01:40:16 -0500 Received: from relay3-d.mail.gandi.net ([217.70.183.195]:60361 "EHLO relay3-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229884AbhCKGkG (ORCPT ); Thu, 11 Mar 2021 01:40:06 -0500 X-Originating-IP: 82.65.183.113 Received: from [172.16.5.113] (82-65-183-113.subs.proxad.net [82.65.183.113]) (Authenticated sender: alex@ghiti.fr) by relay3-d.mail.gandi.net (Postfix) with ESMTPSA id E460E60004; Thu, 11 Mar 2021 06:39:58 +0000 (UTC) Subject: Re: [syzbot] BUG: unable to handle kernel access to user memory in schedule_tail To: Ben Dooks , 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: Alex Ghiti Message-ID: <9a0823f4-de19-c2a2-5333-41c6caadbc11@ghiti.fr> Date: Thu, 11 Mar 2021 01:39:58 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Ben, Le 3/10/21 ? 5:24 PM, Ben Dooks a ?crit?: > 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 (?). > > The unmapped case should have been handled. > > I think this issue is that the check for user-mode access added. From > what I read the code may be wrong in > > +??? if (!user_mode(regs) && addr < TASK_SIZE && > +??????????? unlikely(!(regs->status & SR_SUM))) > +??????? die_kernel_fault("access to user memory without uaccess routines", > +??????????????? addr, regs); > > I think the SR_SUM check might be wrong, as I read the standard the > SR_SUM should be set to disable user-space access. So the check > should be unlikely(regs->status & SR_SUM) to say access without > having disabled the protection. The check that is done seems correct to me: "The SUM (permit Supervisor User Memory access) bit modifies the privilege with which S-mode loads and stores access virtual memory. *When SUM=0, S-mode memory accesses to pages that are accessible by U-mode (U=1 in Figure 4.15) will fault*. When SUM=1, these accesses are permitted.SUM has no effect when page-based virtual memory is not in effect". I will try to reproduce the problem locally. Thanks, Alex > > Without this, you can end up with an infinite loop in the fault handler. > >> >>> Unable to handle kernel access to user memory without uaccess >>> routines at virtual address 000000002749f0d0 >>> Oops [#1] >>> Modules linked in: >>> CPU: 1 PID: 4875 Comm: syz-executor.0 Not tainted >>> 5.12.0-rc2-syzkaller-00467-g0d7588ab9ef9 #0 >>> Hardware name: riscv-virtio,qemu (DT) >>> epc : schedule_tail+0x72/0xb2 kernel/sched/core.c:4264 >>> ? ra : task_pid_vnr include/linux/sched.h:1421 [inline] >>> ? ra : schedule_tail+0x70/0xb2 kernel/sched/core.c:4264 >>> epc : ffffffe00008c8b0 ra : ffffffe00008c8ae sp : ffffffe025d17ec0 >>> ? gp : ffffffe005d25378 tp : ffffffe00f0d0000 t0 : 0000000000000000 >>> ? t1 : 0000000000000001 t2 : 00000000000f4240 s0 : ffffffe025d17ee0 >>> ? s1 : 000000002749f0d0 a0 : 000000000000002a a1 : 0000000000000003 >>> ? a2 : 1ffffffc0cfac500 a3 : ffffffe0000c80cc a4 : 5ae9db91c19bbe00 >>> ? a5 : 0000000000000000 a6 : 0000000000f00000 a7 : ffffffe000082eba >>> ? s2 : 0000000000040000 s3 : ffffffe00eef96c0 s4 : ffffffe022c77fe0 >>> ? s5 : 0000000000004000 s6 : ffffffe067d74e00 s7 : ffffffe067d74850 >>> ? s8 : ffffffe067d73e18 s9 : ffffffe067d74e00 s10: ffffffe00eef96e8 >>> ? s11: 000000ae6cdf8368 t3 : 5ae9db91c19bbe00 t4 : ffffffc4043cafb2 >>> ? t5 : ffffffc4043cafba t6 : 0000000000040000 >>> status: 0000000000000120 badaddr: 000000002749f0d0 cause: >>> 000000000000000f >>> Call Trace: >>> [] schedule_tail+0x72/0xb2 kernel/sched/core.c:4264 >>> [] ret_from_exception+0x0/0x14 >>> Dumping ftrace buffer: >>> ??? (ftrace buffer empty) >>> ---[ end trace b5f8f9231dc87dda ]--- >>> >>> >>> --- >>> This report is generated by a bot. It may contain errors. >>> See https://goo.gl/tpsmEJ for more information about syzbot. >>> syzbot engineers can be reached at syzkaller@googlegroups.com. >>> >>> syzbot will keep track of this issue. See: >>> https://goo.gl/tpsmEJ#status for how to communicate with syzbot. >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "syzkaller-bugs" group. >>> To unsubscribe from this group and stop receiving emails from it, >>> send an email to syzkaller-bugs+unsubscribe@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/syzkaller-bugs/000000000000b74f1b05bd316729%40google.com. >>> >> >> _______________________________________________ >> linux-riscv mailing list >> linux-riscv@lists.infradead.org >> http://lists.infradead.org/mailman/listinfo/linux-riscv >> > >