(2013/12/04 17:45), Ingo Molnar wrote: > > * Masami Hiramatsu <masami.hiramatsu...@hitachi.com> wrote: > >> Hi, >> Here is the version 4 of NOKPORBE_SYMBOL series. >> >> In this version, I removed the cleanup patches and >> add bugfixes I've found, since those bugs will be >> critical. >> >> Rest of the cleanup and visible blacklists will be proposed later in >> another series. > > Ok, let me make it clear: we need _both_ the conceptual cleanups and > the bug fixes.
I see. Why I split this out is because it includes an RFC patch, and for easier review. I still have a series of cleanups :) > Right now kprobes are restricted to root, and they are unsafe and > buggy, and rather fundamentally so, because probing cannot be done > safely without potentially crashing the kernel. So there's no > 'regression' to be fixed, it's mostly about pre-existing bugs - so > there's no requirement for them to come before maintainability > cleanups. OK, I think the kprobe is like a strong medicine, not a toy, since it can intercept most of the kernel functions which may process a sensitive user private data. Thus even if we fix all bugs and make it safe, I don't think we can open it for all users (of course, there should be a knob to open for any or restricted users.) > So we need both a maintainable and a sane/safe solution, and I'd like > to apply the whole thing at once and be at ease that the solution is > round. We should have done this years ago. For the safeness of kprobes, I have an idea; introduce a whitelist for dynamic events. AFAICS, the biggest unstable issue of kprobes comes from putting *many* probes on the functions called from tracers. It doesn't crash the kernel but slows down so much, because every probes hit many other nested miss-hit probes. This gives us a big performance impact. However, on the other side, this kind of feature can be used *for debugging* static trace events by dynamic one if we carefully use a small number of probes on such functions. :) Thus, I think we can restrict users from probing such functions by using a whitelist which ftrace does already have; available_filter_functions :) Then, I'd like to propose this new whitelist feature in kprobe-tracer (not raw kprobe itself). And a sysctl knob for disabling the whitelist. That knob will be /proc/sys/debug/kprobe-event-whitelist and disabling it will mark kernel tainted so that we can check it from bug reports. > So could you please send a whole series that I can apply to -tip as a > work in progress tree, and then we can see what is left to be solved? Sure. :) BTW, would I better fold the cleanups for reducing the number of patches? Thank you, -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu...@hitachi.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
