linux-kernel - Re: livepatch/kprobes incompatibility

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Message-ID: <20160825160814.5gawgk4222vusrj5@treble>
Date:   Thu, 25 Aug 2016 11:08:14 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Jessica Yu <jeyu@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: livepatch/kprobes incompatibility

On Wed, Aug 24, 2016 at 11:39:59AM +0200, Petr Mladek wrote:
>   + kretprobe is safe as well; the kprobe handler does not modify regs->ip;
>     it just modifies the return address from the function; it does not affect
>     livepatching because the address is defined by the function caller
>     and livepatching keeps it as is

BTW, I think there's still a kretprobe issue which affects the accuracy
of the unwinder and the consistency model.  The unwinder will report
kretprobe_trampoline instead of the real caller's return address.

It can probably be fixed similarly to how ftrace function_graph tracing
does it with a ftrace_graph_ret_addr() helper:

  https://lkml.kernel.org/r/cover.1471607358.git.jpoimboe@redhat.com

-- 
Josh