Messages in this thread | | | Date | Tue, 18 Aug 2009 20:19:33 -0400 | From | Masami Hiramatsu <> | Subject | Re: [PATCH -tip v14 03/12] kprobes: checks probe address is instruction boudary on x86 |
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Frederic Weisbecker wrote: > On Tue, Aug 18, 2009 at 07:17:39PM -0400, Masami Hiramatsu wrote: >> Frederic Weisbecker wrote: >>>> + while (addr < paddr) { >>>> + kernel_insn_init(&insn, (void *)addr); >>>> + insn_get_opcode(&insn); >>>> + >>>> + /* Check if the instruction has been modified. */ >>>> + if (insn.opcode.bytes[0] == BREAKPOINT_INSTRUCTION) { >>>> + ret = recover_probed_instruction(buf, addr); >>> >>> >>> >>> I'm confused about the reason of this recovering. Is it to remove >>> kprobes behind the current setting one in the current function? >> >> No, it recovers just an instruction which is probed by a kprobe, >> because we need to know the first byte of this instruction for >> decoding it.
Ah, sorry, it was not accurate. the function recovers an instruction on the buffer(buf), not on the real kernel text. :)
>> >> Perhaps we'd better to have more generic interface (text_peek?) >> for it because another subsystem (e.g. kgdb) may want to insert int3... >> >> Thank you, > > > Aah, I see now, it's to keep a sane check of the instructions > boundaries without int 3 artifacts in the middle. > > But in that case, you should re-arm the breakpoint after your > check, right? > > Or may be you could do the check without repatching?
Yes, it doesn't modify kernel text, just recover an original instruction from kernel text and backup byte on a buffer.
> May be by doing a copy of insn.opcode.bytes and replacing bytes[0] > with what a random kprobe has stolen?
Hm, no, this function is protected from other kprobes by kprobe_mutex.
Thank you,
-- Masami Hiramatsu
Software Engineer Hitachi Computer Products (America), Inc. Software Solutions Division
e-mail: mhiramat@redhat.com
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