[RFC][Patch 0/2][take3]kprobe: kprobe-booster against 2.6.15-rc5-mm3 for i386

[Masami Hiramatsu <hiramatu at sdl dot hitachi dot co dot jp>]

Hi,

I send a couple of patches of kprobe-booster and a patch
of kretprobe-booster in next mails.

If they are good enough, I will post these patches to LKML.


 With kprobe-booster patch, kprobes execute a copied
instruction directly and (if need) jump back to original code.
 This direct execution is executed when the kprobe don't have
both post_handler and break_handler, and the copied instruction
can be executed directly.

I sorted instructions which can be executed directly;
- Call instructions are NG. We should correct the return
  address pushed into top of stack.
- Indirect instructions except for absolute indirect-jumps
  are NG. Those instructions changes EIP randomly. We should
  check EIP and correct it.
- Instructions that change EIP beyond the range of the
  instruction buffer are NG.
- Instructions that change EIP to tail 5 bytes of the
  instruction buffer (it is the size of a jump instruction).
  We must write a jump instruction which backs to original
  kernel code in the instruction buffer.
- Break point instruction is NG. We should not touch EIP and
  pass to other handlers.
- Absolute direct/indirect jumps are OK.- Conditional Jumps are NG.
- Halt and software-interruptions are NG. Because it will stay on
  the instruction buffer of kprobes.
- Prefixes are NG.
- Unknown/reserved opcode is NG.
- Other 1 byte instructions are OK. But those instructions need a
  jump back code.
- 2 bytes instructions are mapped sparsely. So, in this release,
  this patch don't boost those instructions.

>From Intel's IA-32 opcode map described in IA-32 Intel
Architecture Software Developer's Manual Vol.2 B,
I determined that following opcodes are not boostable.
- 0FH (2byte escape)
- 70H - 7FH (Jump on condition)
- 9AH (Call) and 9CH (Pushf)
- C0H-C1H (Grp 2: includes reserved opcode)
- C6H-C7H (Grp11: includes reserved opcode)
- CCH-CEH (Software-interrupt)
- D0H-D3H (Grp2: includes reserved opcode)
- D6H (Reserved)
- D8H-DFH (Coprocessor)
- E0H-E3H (loop/conditional jump)
- E8H (Call)
- F0H-F3H (Prefixes and reserved)
- F4H (Halt)
- F6H-F7H (Grp3: includes reserved opcode)
- FEH-FFH(Grp4,5: includes reserved opcode)

Kprobe-booster checks whether target instruction can
be boost (executed directly) at arch_copy_kprobe()
function. If the target instruction can be boost, it
clears "boostable" flag. If not, it sets "boostable"
flag -1. This is disabled status.
 In resume_execution() function, If "boostable" flag is
cleared,  kprobe-booster measures the size of the target
instruction and sets "boostable" flag 1.

In kprobe_handler(), kprobe checks the "boostable" flag.
If the flag is 1, it resets current kprobe and executes
instruction buffer directly instead of single stepping.

When unregistering a boosted kprobe, it calls synchronize_sched()
after "int3" is removed. So we can ensure followings after
the synchronize_sched() called.
- interrupt handlers are finished on all CPUs.
- instruction buffer is not executed on all CPUs.
And we can release the boosted kprobe safely.

And also, on preemptible kernel, the booster is not enabled
where the kernel preemption is enabled. So, there are no
preempted threads on the instruction buffer.

Best Regards,

-- 
Masami HIRAMATSU
2nd Research Dept.
Hitachi, Ltd., Systems Development Laboratory
E-mail: hiramatu@sdl.hitachi.co.jp