linux-kernel - Re: WARNING in syscall_exit_to_user

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Date:   Sun, 13 Sep 2020 21:54:34 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        syzbot <syzbot+7ffc7214b893651d52b8@...kaller.appspotmail.com>,
        syzkaller-bugs@...glegroups.com, Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: WARNING in syscall_exit_to_user_mode

On Sat, Sep 12 2020 at 10:52, Kees Cook wrote:
>> ------------[ cut here ]------------
>> syscall 56 left IRQs disabled
>
> This WARN appears reachable. :)

The above is hardly a problem of the new entry code. It's just detecting
the wreckage...

> I also see on the dashboard these other problems with the new entry
> code:

This one is also just the messenger. That's the

     lockdep_assert_irqs_disabled();

in irqentry_exit() if I'm reading the reports correctly. That's a #PF
returning with interrupts enabled for whatever weird reason. Let me
stare at that...

> https://syzkaller.appspot.com/bug?extid=d4336c84ed0099fdbe47

This one is not a new entry code problem either:

> https://syzkaller.appspot.com/bug?extid=c4af95386364bc59b13e

INFO: task syz-executor.0:5956 can't die for more than 143 seconds.
task:syz-executor.0  state:R  running task     stack:25424 pid: 5956 ppid: 14284 flags:0x00004004
Call Trace:
 context_switch kernel/sched/core.c:3778 [inline]
 __schedule+0x8e5/0x21e0 kernel/sched/core.c:4527
 preempt_schedule_irq+0xb0/0x150 kernel/sched/core.c:4785
 irqentry_exit_cond_resched kernel/entry/common.c:333 [inline]
 irqentry_exit_cond_resched kernel/entry/common.c:325 [inline]
 irqentry_exit+0x65/0x90 kernel/entry/common.c:363
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:581
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:653 [inline]
RIP: 0010:lock_acquire+0x27b/0xad0 kernel/locking/lockdep.c:5008
Code: 00 00 00 00 fc ff df 48 c1 e8 03 80 3c 10 00 0f 85 f8 06 00 00 48 83 3d 6a d1 5b 08 00 0f 84 a6 05 00 00 48 8b 7c 24 08 57 9d <0f> 1f 44 00 00 48 b8 00 00 00 00 00 fc ff df 48 03 44 24 10 48 c7
RSP: 0018:ffffc900088477c0 EFLAGS: 00000286
RAX: 1ffffffff136c7d9 RBX: ffff88808766c200 RCX: 000000005603e267
RDX: dffffc0000000000 RSI: 0000000000000001 RDI: 0000000000000286
RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff8c6a59e7
R10: fffffbfff18d4b3c R11: 0000000000000001 R12: 0000000000000002
R13: ffffffff89c67640 R14: 0000000000000000 R15: ffff88808766c200
 rcu_lock_acquire include/linux/rcupdate.h:248 [inline]
 rcu_read_lock include/linux/rcupdate.h:641 [inline]
 inet_twsk_purge+0x112/0x7c0 net/ipv4/inet_timewait_sock.c:268
 ops_exit_list+0x10d/0x160 net/core/net_namespace.c:189
 setup_net+0x508/0x850 net/core/net_namespace.c:364
 copy_net_ns+0x31e/0x760 net/core/net_namespace.c:482
 create_new_namespaces+0x3f6/0xb20 kernel/nsproxy.c:110

The new entry code is just in the stack trace because that task was
preempted after a timer interrupt.

Thanks,

        tglx