Kprobes: pre-handler with interrupts enabled - is it possible?
From: Eugene Shatokhin
Date: Mon Feb 23 2015 - 10:11:29 EST
First of all, many thanks to the developers of Kprobes! I use both
Kprobes and parts of their code a lot in my projects these days.
As far as I can see, the pre-handlers of Kprobes run with interrupts and
preemption disabled on the given CPU, at least on x86 without Kprobe
Is it possible, however, to use Kprobes to somehow execute my code
before a given instruction but with the same restrictions as the
original instruction, at least, w.r.t. the interrupts?
I mean, if the instruction is executed with interrupts enabled, my code
would also execute with interrupts enabled, etc.
If it is possible, how would you recommend to do that? Without patching
the implementation of Kprobes, I mean.
Same for preemption, but, it seems, Kprobes really need it disabled, at
least to be able to use kprobe_running() and other per-cpu data.
In RaceHound project I am now working on
(https://github.com/winnukem/racehound/tree/rh_rework), the breakpoints
are used to detect data races in the kernel code in runtime. Software
breakpoints for the code, hardware breakpoints for the data that is
about to be accessed.
However, to make it all work, the detector introduces delays before the
instructions of interest. I could do this in Kprobes' pre-handlers but
the interrupts would always be disabled on the current CPU during the
delays, which is no good.
So far, I implemented it using software breakpoints directly, without
Kprobes. The pre-handlers are executed then in the same context as the
Still the implementation becomes more and more like Kprobes in some
places over time. If there is a way to avoid reinventing the wheel and
just use Kprobes, I would do that.
So, any ideas?
Eugene Shatokhin, ROSA
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