kernel-hardening - Re: [PATCH 1/1] stackleak: Disable ftrace for stackleak.c

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Message-ID: <eeb7f5ee-1e2e-d37b-cca2-e0a29826e8eb@linux.com>
Date: Sun, 11 Nov 2018 13:19:45 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: 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

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

Best regards,
Alexander

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