Date: Mon, 12 Nov 2018 09:53:29 -0500 (EST) From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com> To: Masami Hiramatsu <mhiramat@...nel.org>, rostedt <rostedt@...dmis.org> Cc: Alexander Popov <alex.popov@...ux.com>, kernel-hardening <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>, Dan Williams <dan.j.williams@...el.com>, Masahiro Yamada <yamada.masahiro@...ionext.com>, x86 <x86@...nel.org>, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 1/1] stackleak: Disable ftrace for stackleak.c ----- On Nov 11, 2018, at 9:50 PM, Masami Hiramatsu mhiramat@...nel.org wrote: > 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. Just to clarify: AFAIU you guys are recommending to add _both_ a "notrace" annotation to stackleak_erase() _and_ a NOKPROBE_SYMBOL(stackleak_erase), so neither function tracing nor kprobes can hook on that function. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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