lkml.org 
[lkml]   [2018]   [May]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH -tip v4 24/27] bpf: error-inject: kprobes: Clear current_kprobe and enable preempt in kprobe
Masami Hiramatsu wrote:
> Clear current_kprobe and enable preemption in kprobe
> even if pre_handler returns !0.
>
> This simplifies function override using kprobes.
>
> Jprobe used to require to keep the preemption disabled and
> keep current_kprobe until it returned to original function
> entry. For this reason kprobe_int3_handler() and similar
> arch dependent kprobe handers checks pre_handler result
> and exit without enabling preemption if the result is !0.
>
> After removing the jprobe, Kprobes does not need to
> keep preempt disabled even if user handler returns !0
> anymore.

I think the reason jprobes did it that way is to address architecture
specific requirements when changing a function. So, without that
infrastructure, I am not sure if we will be able to claim support for
over-riding functions with kprobes. I am not sure if we want to claim
that, but this is something we need to be clear on.

For powerpc, the current function override in error-inject works fine
since the new function does nothing. But, if anyone wants to do more
work in the replacement function, it won't work with the current
approach.

>
> But since the function override handler in error-inject
> and bpf is also returns !0 if it overrides a function,
> to balancing the preempt count, it enables preemption
> and reset current kprobe by itself.
>
> That is a bad design that is very buggy. This fixes
> such unbalanced preempt-count and current_kprobes setting
> in kprobes, bpf and error-inject.
>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
> arch/arc/kernel/kprobes.c | 5 +++--
> arch/arm/probes/kprobes/core.c | 10 +++++-----
> arch/arm64/kernel/probes/kprobes.c | 10 +++++-----
> arch/ia64/kernel/kprobes.c | 13 ++++---------
> arch/mips/kernel/kprobes.c | 4 ++--
> arch/powerpc/kernel/kprobes.c | 7 +++++--

I think you should also update arch/powerpc/kernel/kprobes-ftrace.c

- Naveen


\
 
 \ /
  Last update: 2018-05-31 12:57    [W:0.150 / U:1.056 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site