linux-kernel - Re: [RFC][PATCH 3/7] kprobes: Remove kretprobe hash

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Message-ID: <20200828135824.GD1362448@hirez.programming.kicks-ass.net>
Date:   Fri, 28 Aug 2020 15:58:24 +0200
From:   peterz@...radead.org
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     "Eddy_Wu@...ndmicro.com" <Eddy_Wu@...ndmicro.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "naveen.n.rao@...ux.ibm.com" <naveen.n.rao@...ux.ibm.com>,
        "anil.s.keshavamurthy@...el.com" <anil.s.keshavamurthy@...el.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "cameron@...dycamel.com" <cameron@...dycamel.com>,
        "oleg@...hat.com" <oleg@...hat.com>,
        "will@...nel.org" <will@...nel.org>,
        "paulmck@...nel.org" <paulmck@...nel.org>
Subject: Re: [RFC][PATCH 3/7] kprobes: Remove kretprobe hash

On Fri, Aug 28, 2020 at 10:51:13PM +0900, Masami Hiramatsu wrote:
 
> 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
> 4) task2 returns to the kretprobe_trampoline
> 5) Bomb!
> 
> Hmm, we need to fixup the kernel stack when copying process. 

How would that scenario have been avoided in the old code? Because there
task2 would have a different has and not have found a kretprobe_instance
either.