Messages in this thread | | | Subject | Re: [PATCH -tip v6 26/27] Documentation: kprobes: Add how to change the execution path | From | Randy Dunlap <> | Date | Tue, 19 Jun 2018 09:31:49 -0700 |
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On 06/19/2018 09:16 AM, Masami Hiramatsu wrote: > Add a section that explaining how to change the execution > path with kprobes and warnings for some arch. > > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> > Cc: Jonathan Corbet <corbet@lwn.net> > Cc: linux-doc@vger.kernel.org > --- > Documentation/kprobes.txt | 20 ++++++++++++++++++++ > 1 file changed, 20 insertions(+) > > diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt > index 3e9e99ea751b..8a98eed1521b 100644 > --- a/Documentation/kprobes.txt > +++ b/Documentation/kprobes.txt > @@ -80,6 +80,26 @@ After the instruction is single-stepped, Kprobes executes the > "post_handler," if any, that is associated with the kprobe. > Execution then continues with the instruction following the probepoint. >
Hi, I have a few small suggestions...
> +Changing Execution Path > +----------------------- > + > +Since the kprobes can probe into a running kernel code, it can change
Since kprobes can probe into running kernel code, it can change
> +the register set, including instruction pointer. This operation > +requires maximum attention, such as keeping the stack frame, recovering > +execution path etc. Since it is operated on running kernel and need deep
Since it operates on a running kernel and needs deep
> +knowladge of the archtecture and concurrent computing, you can easily
knowledge of the architecture
> +shot your foot.
shoot
> + > +If you change the instruction pointer (and set up other related > +registers) in pre_handler, you must return !0 so that the kprobes
so that kprobes
> +stops single stepping and just returns to given address.
to the given address.
> +This also means post_handler should not be called anymore. > + > +Note that this operation may be harder on some architectures which > +use TOC (Table of Contents) for function call, since you have to > +setup new TOC for your function in your module, and recover old
setup a new TOC for your function in your module, and recover the old
> +one after back from it.
one after returning from it.
> + > Return Probes > -------------
-- ~Randy
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