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Message-Id: <20181112115058.39e98750750c91eeb349cfdf@kernel.org>
Date: Mon, 12 Nov 2018 11:50:58 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Alexander Popov <alex.popov@...ux.com>,
kernel-hardening@...ts.openwall.com, Kees Cook <keescook@...omium.org>,
Jann Horn <jannh@...gle.com>, Ingo Molnar <mingo@...nel.org>, Andy
Lutomirski <luto@...nel.org>, Joerg Roedel <joro@...tes.org>, Borislav
Petkov <bp@...en8.de>, Thomas Gleixner <tglx@...utronix.de>, Dave Hansen
<dave.hansen@...ux.intel.com>, Peter Zijlstra <peterz@...radead.org>, Jan
Kara <jack@...e.cz>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Dan Williams <dan.j.williams@...el.com>, Masahiro Yamada
<yamada.masahiro@...ionext.com>, Masami Hiramatsu <mhiramat@...nel.org>,
x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] stackleak: Disable ftrace for stackleak.c
Hi Alexander and Steve,
On Sun, 11 Nov 2018 20:53:51 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:
> On Sun, 11 Nov 2018 13:19:45 +0300
> Alexander Popov <alex.popov@...ux.com> wrote:
>
> > On 11.11.2018 2:30, Steven Rostedt wrote:
> > > On Sun, 11 Nov 2018 01:05:30 +0300
> > > Alexander Popov <alex.popov@...ux.com> wrote:
> > >
> > >> The stackleak_erase() function is called on the trampoline stack at the
> > >> end of syscall. This stack is not big enough for ftrace operations,
> > >> e.g. it can be overflowed if we enable kprobe_events for stackleak_erase().
> > >
> > > Is the issue with kprobes or with function tracing? Because this stops
> > > function tracing which I only want disabled if function tracing itself
> > > is an issue, not for other things that may use the function tracing
> > > infrastructure.
> >
> > Hello Steven,
> >
> > I believe that stackleak erasing is not compatible with function tracing itself.
> > That's what the kernel testing robot has hit:
> > https://www.openwall.com/lists/kernel-hardening/2018/11/09/1
> >
> > I used kprobe_events just to reproduce the problem:
> > https://www.openwall.com/lists/kernel-hardening/2018/11/09/4
>
> Have you tried adding a "notrace" to stackleak_erase()?
>
> Not tracing the entire file is a bit of overkill. There's no reason
> ftrace can't trace stack_erasing_sysctl() or perhaps even
> stackleak_track_stack() as that may be very interesting to trace.
I think it is not enough for stopping kprobes. If you want to stop the kprobes
(int3 version) on stackleak_erase(), you should use NOKPROBE_SYMBOL(stackleak_erase),
since kprobes can work without ftrace.
Thank you,
--
Masami Hiramatsu <mhiramat@...nel.org>
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