Re: [PATCH -tip v6 26/27] Documentation: kprobes: Add how to change the execution path
From: Randy Dunlap <hidden>
Date: 2018-06-19 16:31:58
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On 06/19/2018 09:16 AM, Masami Hiramatsu wrote:
quoted hunk ↗ jump to hunk
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