linux-kernel - RE: x86/kprobes: kretprobe fails to triggered if kprobe at function entry is not optimized (trigger by int3 breakpoint)

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Date:   Wed, 26 Aug 2020 13:36:15 +0000
From:   "Eddy_Wu@...ndmicro.com" <Eddy_Wu@...ndmicro.com>
To:     "peterz@...radead.org" <peterz@...radead.org>
CC:     "mhiramat@...nel.org" <mhiramat@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
Subject: RE: x86/kprobes: kretprobe fails to triggered if kprobe at function
 entry is not optimized (trigger by int3 breakpoint)

> -----Original Message-----
> From: peterz@...radead.org <peterz@...radead.org>
> Sent: Wednesday, August 26, 2020 6:26 PM
> To: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: Eddy Wu (RD-TW) <Eddy_Wu@...ndmicro.com>; linux-kernel@...r.kernel.org; x86@...nel.org
> Subject: Re: x86/kprobes: kretprobe fails to triggered if kprobe at function entry is not optimized (trigger by int3 breakpoint)
>
> On Wed, Aug 26, 2020 at 07:00:41PM +0900, Masami Hiramatsu wrote:
> > Of course, this doesn't solve the llist_del_first() contention in the
> > pre_kretprobe_handler(). So anyway we need a lock for per-probe llist
> > (if I understand llist.h comment correctly.)
>
> Bah, lemme think about that. Kprobes really shouldn't be using locks :/

Maybe we can have per-cpu free list for retprobe_instance?
This ensure we only have one user requesting free instance at a time, given that pre_kretprobe_handler() wont recursive.

We may be wasting memory if target function perfer some cpu though.

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