From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Sun, 11 Nov 2018 20:53:51 -0500
From: Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 1/1] stackleak: Disable ftrace for stackleak.c
Message-ID: <20181111205351.1874bb1e@vmware.local.home>
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To: Alexander Popov <alex.popov@linux.com>
Cc: kernel-hardening@lists.openwall.com, Kees Cook <keescook@chromium.org>, Jann Horn <jannh@google.com>, Ingo Molnar <mingo@kernel.org>, Andy Lutomirski <luto@kernel.org>, Joerg Roedel <joro@8bytes.org>, Borislav Petkov <bp@alien8.de>, Thomas Gleixner <tglx@linutronix.de>, Dave Hansen <dave.hansen@linux.intel.com>, Peter Zijlstra <peterz@infradead.org>, Jan Kara <jack@suse.cz>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Dan Williams <dan.j.williams@intel.com>, Masahiro Yamada <yamada.masahiro@socionext.com>, Masami Hiramatsu <mhiramat@kernel.org>, x86@kernel.org, linux-kernel@vger.kernel.org
List-ID: <kernel-hardening.lists.openwall.com>

On Sun, 11 Nov 2018 13:19:45 +0300
Alexander Popov <alex.popov@linux.com> wrote:

> On 11.11.2018 2:30, Steven Rostedt wrote:
> > On Sun, 11 Nov 2018 01:05:30 +0300
> > Alexander Popov <alex.popov@linux.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.

-- Steve