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

[Li Bin]

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
> 
> 
> 
> 
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> .
>