Messages in this thread | | | Date | Tue, 24 Feb 2015 14:10:35 +0100 | From | Petr Mladek <> | Subject | Re: [PATCH ftrace/core v6 4/5] kprobes: Set IPMODIFY flag only if the probe can change regs->ip |
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On Tue 2015-02-24 20:47:06, Masami Hiramatsu wrote: > (2015/02/24 17:52), Petr Mladek wrote: > > On Tue 2015-02-24 16:38:18, Masami Hiramatsu wrote: > >> Hi Petr, > >> > >> Sorry I missed this mail. > > > > Thanks a lot for answering it with many valuable information. > > > >> (2015/01/27 1:14), Petr Mladek wrote:> On Fri 2014-11-21 05:25:30, Masami Hiramatsu wrote: > >>>> Set FTRACE_OPS_FL_IPMODIFY flag only for the probes which can change > >>>> regs->ip, which has kprobe->break_handler. > >>>> Currently we can not put jprobe and another ftrace handler which > >>>> changes regs->ip on the same function because all kprobes have > >>>> FTRACE_OPS_FL_IPMODIFY flag. This removes FTRACE_OPS_FL_IPMODIFY > >>>> flag from kprobes and only when the user uses jprobe (or the > >>>> kprobe.break_handler != NULL) we add additinal ftrace_ops with > >>>> FTRACE_OPS_FL_IPMODIFY on target function. > >>> > >>> Please, what are the plans with this patch? > >> > >> Well, I'll revise this for newer kernel. > >>> > >>> I have checked the interference between Kprobes and LivePatching and > >>> here is my observation: [...] > >>> 2. Normal Kprobe for the original function is ignored if the function > >>> is patched. > >>> > >>> I am working on a code that will print warning in both > >>> cases. First, when we add a patch and the function has > >>> a Kprobe registered. Second, the function is patched and > >>> we want to add Kprobe for the original version. > >> > >> Thanks! Maybe we can add "Ignored" flag for those kprobes so that users > >> can check it is working or not via debugfs. > > > > Great idea. Well, it will solve only already existing Kprobes. > > Yeah, just changing the kprobe state is easy and needed. > And for newer kprobes, perhaps we need to add > bool klp_patched_function(void *func_addr); to check the > function is patched. (this will need to be done with > locking kpatch...)
I like this idea and will try to use it once I get time again.
> >>> I want to make it generic and make it dependent on the > >>> IPMODIFY flag. IMHO, it just could be a handshake between > >>> kprobe and ftrace code. I am still trying to understand > >>> the needed parts of the code ;-) > > > > I have played with it and realized that only Kprobes framework has > > information about all existing and newly created Kprobes. Therefore > > we need to somehow inform it that there is a patch and that the code > > is redirected. I have a prototype that is introducing a new fake > > Kprobe, so called Patch Probe. It has new flag KPROBE_FLAG_PATCH > > and no handlers. Conflicts with existing Kprobes are checked when > > this special probe is added. Also conflicts with these Patch probes > > are checked when new normal Kprobe is added. > > No, you don't need that. I can make kprobes_location() or > kprobe_for_each_on(kp, start, end) {} iterator. Since the livepatch > is in-tree feature now, we can change kprobes for it...
You are right, the in-tree live patch code brings more possibilities.
> And anyway, IPMODIFY should be only for jprobes not kprobes...
Yup.
> > I have one more patch set in the queue. It better handle errors when > > kprobe_ftrace_ops could not be registered in arm_kprobe_ftrace() > > and disarm_kprobe_ftrace(). This one is nearly done. Unfortunately, > > I had to interupt it because my wife got sick and I had to take care > > of babies. And then there is the big activity around life patching > > that we need to somehow handle. > > Ah, thanks, and hope your wife to get better soon.
Thanks a lot. Fortunately, she already is better.
Best Regards, Petr
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