Messages in this thread | | | Date | Wed, 19 Aug 2009 02:46:29 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH -tip v14 03/12] kprobes: checks probe address is instruction boudary on x86 |
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On Tue, Aug 18, 2009 at 08:19:33PM -0400, Masami Hiramatsu wrote: > 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. :)
Ah ok. I'll just add a small comment about that then, and apply it.
> >> > >> 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.
Ok.
> > 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,
Right, thanks!
> -- > Masami Hiramatsu > > Software Engineer > Hitachi Computer Products (America), Inc. > Software Solutions Division > > e-mail: mhiramat@redhat.com >
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