Re: [syzbot] BUG: unable to handle kernel access to user memory in schedule_tail

From: Dmitry Vyukov <dvyukov@google.com>
To: syzbot <syzbot+e74b94fe601ab9552d69@syzkaller.appspotmail.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	linux-riscv <linux-riscv@lists.infradead.org>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>,
	Benjamin Segall <bsegall@google.com>,
	dietmar.eggemann@arm.com, Juri Lelli <juri.lelli@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>, Mel Gorman <mgorman@suse.de>,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	Vincent Guittot <vincent.guittot@linaro.org>
Subject: Re: [syzbot] BUG: unable to handle kernel access to user memory in schedule_tail
Date: Wed, 10 Mar 2021 18:16:11 +0100	[thread overview]
Message-ID: <CACT4Y+ZHMYijYAkeLMX=p9jx6pBivJz06h_1rGt-k9=AgfkWQg@mail.gmail.com> (raw)
In-Reply-To: <000000000000b74f1b05bd316729@google.com>

On Wed, Mar 10, 2021 at 5:46 PM syzbot
<syzbot+e74b94fe601ab9552d69@syzkaller.appspotmail.com> 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 (?).

> 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:
> [<ffffffe00008c8b0>] schedule_tail+0x72/0xb2 kernel/sched/core.c:4264
> [<ffffffe000005570>] 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.
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>
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