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Date:   Fri, 28 Aug 2020 16:19:17 +0200
From:   peterz@infradead.org
To:     "Eddy_Wu@trendmicro.com" <Eddy_Wu@trendmicro.com>
Cc:     Masami Hiramatsu <mhiramat@kernel.org>,
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Subject: Re: [RFC][PATCH 3/7] kprobes: Remove kretprobe hash
Message-ID: <20200828141917.GE1362448@hirez.programming.kicks-ass.net>
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On Fri, Aug 28, 2020 at 02:11:18PM +0000, Eddy_Wu@trendmicro.com wrote:
> > From: Masami Hiramatsu <mhiramat@kernel.org>
> >
> > OK, schedule function will be the key. I guess the senario is..
> >
> > 1) kretporbe replace the return address with kretprobe_trampoline on task1's kernel stack
> > 2) the task1 forks task2 before returning to the kretprobe_trampoline
> > 3) while copying the process with the kernel stack, task2->kretprobe_instances.first = NULL
> 
> I think new process created by fork/clone uses a brand new kernel
> stack? I thought only user stack are copied.  Otherwise any process
> launch should crash in the same way

I was under the same impression, we create a brand new stack-frame for
the new task, this 'fake' frame we can schedule into.

It either points to ret_from_fork() for new user tasks, or
kthread_frame_init() for kernel threads.