Re: WARNING in bpf_bprintf_prepare

[Hao Sun]

Jiri Olsa <olsajiri@xxxxxxxxx> 于2022年10月27日周四 19:24写道：
>
> On Thu, Oct 27, 2022 at 10:27:28AM +0800, Hao Sun wrote:
> > Hi,
> >
> > The following warning can be triggered with the C reproducer in the link.
> > Syzbot also reported this several days ago, Jiri posted a patch that
> > uses bpf prog `active` field to fix this by 05b24ff9b2cfab (bpf:
> > Prevent bpf program recursion...) according to syzbot dashboard
> > (https://syzkaller.appspot.com/bug?id=179313fb375161d50a98311a28b8e2fc5f7350f9).
> > But this warning can still be triggered on 247f34f7b803
> > (Linux-v6.1-rc2) that already merged the patch, so it seems that this
> > still is an issue.
> >
> > HEAD commit: 247f34f7b803 Linux 6.1-rc2
> > git tree: upstream
> > console output: https://pastebin.com/raw/kNw8JCu5
> > kernel config: https://pastebin.com/raw/sE5QK5HL
> > C reproducer: https://pastebin.com/raw/X96ASi27
>
> hi,
> right, that fix addressed that issue for single bpf program,
> and it won't prevent if there are multiple programs hook on
> contention_begin tracepoint and calling bpf_trace_printk,
>
> I'm not sure we can do something there.. will check
>
> do you run just the reproducer, or you load the server somehow?
> I cannot hit the issue so far
>

Hi,

Last email has format issues, resend it here.

I built the kernel with the config in the link, which contains
“CONFIG_CMDLINE="earlyprintk=serial net.ifnames=0
sysctl.kernel.hung_task_all_cpu_backtrace=1 panic_on_warn=1 …”, and
boot the kernel with normal qemu setup and then the warning can be
triggered by executing the reproducer.

Also, I’m willing to test the proposed patch if any.

Thanks
Hao

> thanks,
> jirka
>
> >
> > ------------[ cut here ]------------
> > WARNING: CPU: 6 PID: 6850 at kernel/bpf/helpers.c:770
> > try_get_fmt_tmp_buf kernel/bpf/helpers.c:770 [inline]
> > WARNING: CPU: 6 PID: 6850 at kernel/bpf/helpers.c:770
> > bpf_bprintf_prepare+0xf6a/0x1170 kernel/bpf/helpers.c:818
> > Modules linked in:
> > CPU: 6 PID: 6850 Comm: a.out Not tainted 6.1.0-rc2-dirty #23
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> > 1.13.0-1ubuntu1.1 04/01/2014
> > RIP: 0010:try_get_fmt_tmp_buf kernel/bpf/helpers.c:770 [inline]
> > RIP: 0010:bpf_bprintf_prepare+0xf6a/0x1170 kernel/bpf/helpers.c:818
> > Code: c6 e8 ba 51 00 07 83 c0 01 48 98 48 01 c5 48 89 6c 24 08 e8 b8
> > 0a eb ff 8d 6b 02 83 44 24 10 01 e9 2d f5 ff ff e8 a6 0a eb ff <0f> 0b
> > 65 ff 0d 85 bf 7c 7e bf 01 00 00 00 41 bc f0 ff ff ff e8 2d
> > RSP: 0018:ffffc90015a96c20 EFLAGS: 00010046
> > RAX: 0000000000000000 RBX: 0000000000000002 RCX: ffff88814f8057c0
> > RDX: 0000000000000000 RSI: ffff88814f8057c0 RDI: 0000000000000002
> > RBP: ffffc90015a96d50 R08: ffffffff818681ba R09: 0000000000000003
> > R10: 0000000000000005 R11: fffffbfff1a25ab2 R12: 0000000000000003
> > R13: 0000000000000004 R14: ffffc90015a96e08 R15: 0000000000000003
> > FS:  00007f012f4d2440(0000) GS:ffff8880b9d80000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00007f012f19ac28 CR3: 0000000148da3000 CR4: 0000000000350ee0
> > Call Trace:
> >  <TASK>
> >  ____bpf_trace_printk kernel/trace/bpf_trace.c:385 [inline]
> >  bpf_trace_printk+0xab/0x420 kernel/trace/bpf_trace.c:376
> >  bpf_prog_0605f9f479290f07+0x2f/0x33
> >  bpf_dispatcher_nop_func include/linux/bpf.h:963 [inline]
> >  __bpf_prog_run include/linux/filter.h:600 [inline]
> >  bpf_prog_run include/linux/filter.h:607 [inline]
> >  __bpf_trace_run kernel/trace/bpf_trace.c:2254 [inline]
> >  bpf_trace_run2+0x14d/0x3d0 kernel/trace/bpf_trace.c:2293
> >  __bpf_trace_contention_begin+0xb5/0xf0 include/trace/events/lock.h:95
> >  __traceiter_contention_begin+0x56/0x90 include/trace/events/lock.h:95
> >  trace_contention_begin include/trace/events/lock.h:95 [inline]
> >  __pv_queued_spin_lock_slowpath+0x542/0xff0 kernel/locking/qspinlock.c:405
> >  pv_queued_spin_lock_slowpath arch/x86/include/asm/paravirt.h:591 [inline]
> >  queued_spin_lock_slowpath arch/x86/include/asm/qspinlock.h:51 [inline]
> >  queued_spin_lock include/asm-generic/qspinlock.h:114 [inline]
> >  do_raw_spin_lock+0x204/0x2d0 kernel/locking/spinlock_debug.c:115
> >  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:111 [inline]
> >  _raw_spin_lock_irqsave+0x41/0x50 kernel/locking/spinlock.c:162
> >  ____bpf_trace_printk kernel/trace/bpf_trace.c:390 [inline]
> >  bpf_trace_printk+0xcf/0x420 kernel/trace/bpf_trace.c:376
> >  </TASK>
> >
> > Regards
> > Hao Sun