Re: [PATCH v12 00/10] arm64: Add kernel probes (kprobes) support

[David Long]

On 05/11/2016 10:26 PM, Li Bin wrote:
> on 2016/5/11 23:33, James Morse wrote:
> > Hi David,
> >
> > On 27/04/16 19:52, David Long wrote:
> > > From: "David A. Long" <dave.long@xxxxxxxxxx>
> > >
> > > This patchset is heavily based on Sandeepa Prabhu's ARM v8 kprobes patches,
> > > first seen in October 2013. This version attempts to address concerns raised by
> > > reviewers and also fixes problems discovered during testing.
> > >
> > > This patchset adds support for kernel probes(kprobes), jump probes(jprobes)
> > > and return probes(kretprobes) support for ARM64.
> > >
> > > The kprobes mechanism makes use of software breakpoint and single stepping
> > > support available in the ARM v8 kernel.
> >
> > I applied this series on v4.6-rc7, and built the sample kprobes. They work fine,
> > unless I throw ftrace into the mix too.
> >
> > I enabled the function_graph tracer, then tried to load the jprobe example module:
> > -------------------------%<-------------------------
> > root@ubuntu:/sys/kernel/debug/tracing# insmod /root/jprobe_example.ko
> > Planted jprobe at ffffff80080c8f20, handler addr ffffff8000bb3000
> > root@ubuntu:/sys/kernel/debug/tracing# jprobe: clone_flags = 0x1200011, stack_st
> > art = 0x0 stack_size = 0x0
> > Bad mode in Synchronous Abort handler detected, code 0x86000005 -- IABT (current
> >   EL)
> > CPU: 5 PID: 1047 Comm: systemd-udevd Not tainted 4.6.0-rc7+ #4064
> > Hardware name: ARM Juno development board (r1) (DT)
> > task: ffffffc975948300 ti: ffffffc974e4c000 task.ti: ffffffc974e4c000
> > PC is at 0x0
> > LR is at 0x0
> >
> > pc : [<0000000000000000>] lr : [<0000000000000000>] pstate: 60000145
> > sp : ffffffc974e4ff00
> > x29: 0000000001200011 x28: ffffffc974e4c000
> > x27: ffffff80088d0000 x26: 00000000000000dc
> > x25: 0000000000000120 x24: 0000000000000015
> > x23: 0000000060000000 x22: 0000007fa1b40e60
> > x21: 0000007fa1ce70d0 x20: 0000000000000000
> > x19: 0000000000000000 x18: 0000000000000a03
> > x17: 0000007fa1b40d90 x16: ffffff80080c9708
> > x15: 003b9aca00000000 x14: 0000007fddb7e5c0
> > x13: 0000007fa1b40e2c x12: 0000000000d00ff0
> > x11: ffffff8009c4d000 x10: ffffff800920c000
> > x9 : ffffff8008f5c000 x8 : ffffffc976c06800
> > x7 : 000000000006daf2 x6 : 0000000000000015
> > x5 : 0000000000000004 x4 : ffffffc96e8690a0
> > x3 : 0000001ed7cbab74 x2 : ffffffc96e869000
> > x1 : 0000000000000000 x0 : 0000000000000000
> >
> > Internal error: Oops - bad mode: 0 [#1] PREEMPT SMP
> > Modules linked in: jprobe_example
> > CPU: 5 PID: 1047 Comm: systemd-udevd Not tainted 4.6.0-rc7+ #4064
> > Hardware name: ARM Juno development board (r1) (DT)
> > task: ffffffc975948300 ti: ffffffc974e4c000 task.ti: ffffffc974e4c000
> > PC is at 0x0
> > LR is at 0x0
> >
> > pc : [<0000000000000000>] lr : [<0000000000000000>] pstate: 60000145
> > sp : ffffffc974e4ff00
> > x29: 0000000001200011 x28: ffffffc974e4c000
> > x27: ffffff80088d0000 x26: 00000000000000dc
> > x25: 0000000000000120 x24: 0000000000000015
> > x23: 0000000060000000 x22: 0000007fa1b40e60
> > x21: 0000007fa1ce70d0 x20: 0000000000000000
> > x19: 0000000000000000 x18: 0000000000000a03
> > x17: 0000007fa1b40d90 x16: ffffff80080c9708
> > x15: 003b9aca00000000 x14: 0000007fddb7e5c0
> > x13: 0000007fa1b40e2c x12: 0000000000d00ff0
> > x11: ffffff8009c4d000 x10: ffffff800920c000
> > x9 : ffffff8008f5c000 x8 : ffffffc976c06800
> > x7 : 000000000006daf2 x6 : 0000000000000015
> > x5 : 0000000000000004 x4 : ffffffc96e8690a0
> > x3 : 0000001ed7cbab74 x2 : ffffffc96e869000
> > x1 : 0000000000000000 x0 : 0000000000000000
> >
> > Process systemd-udevd (pid: 1047, stack limit = 0xffffffc974e4c020)
> > Stack: (0xffffffc974e4ff00 to 0xffffffc974e50000)
> > ff00: 0000000000000417 0000007fa1ce76f0 00000000000000dc 0000000000000417
> > ff20: 00000000ffffffff 0000007fddb7ecf8 0000000000000005 ffffffffffffffff
> > ff40: 00000000ff000001 003b9aca00000000 000000555b3868b0 0000007fa1b40d90
> > ff60: 0000000000000a03 0000007fddb7e5c0 0000000000000000 0000007fddb7e5e0
> > ff80: 000000555b358000 000000558f56f0e0 0000000000000000 000000558f574f00
> > ffa0: 000000558f574f00 00000000000004fa 000000558f56f010 0000007fddb7e600
> > ffc0: 0000007fa1b40e2c 0000007fddb7e5c0 0000007fa1b40e60 0000000060000000
> > ffe0: 0000000001200011 00000000000000dc 0004000084000200 0800000002000000
> > Call trace:
> > [<          (null)>]           (null)
> > Code: bad PC value
> > ---[ end trace 35d24aad799c2941 ]---
> > -------------------------%<-------------------------
>
> To solve this, it should pause function tracing before the jprobe handler is called
> and unpause it before it returns back to the function it probed.
>
> diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c
> index db2d95c..b21ed00 100644
> --- a/arch/arm64/kernel/kprobes.c
> +++ b/arch/arm64/kernel/kprobes.c
> @@ -714,6 +714,7 @@ int __kprobes setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
>
>          instruction_pointer_set(regs, (long)jp->entry);
>          preempt_disable();
> +       pause_graph_tracing();
>          return 1;
>   }
>
> @@ -757,6 +758,7 @@ int __kprobes longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
>                          show_regs(regs);
>                          BUG();
>                  }
> +               unpause_graph_tracing();
>                  *regs = kcb->jprobe_saved_regs;
>                  memcpy((void *)stack_addr, kcb->jprobes_stack,
>                         MIN_STACK_SIZE(stack_addr));
>
>
> Li Bin
>
> > Thanks,
> >
> >
> > James


Thanks for the suggested fix.

-dl