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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