linux-kernel - Re: [PATCH v11 04/12] scs: disable when function graph tracing is enabled

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Message-ID: <20200420152306.2d45e3c4@gandalf.local.home>
Date:   Mon, 20 Apr 2020 15:23:06 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dave Martin <Dave.Martin@....com>,
        Kees Cook <keescook@...omium.org>,
        Laura Abbott <labbott@...hat.com>,
        Marc Zyngier <maz@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Jann Horn <jannh@...gle.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        clang-built-linux@...glegroups.com,
        kernel-hardening@...ts.openwall.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v11 04/12] scs: disable when function graph tracing is
 enabled

On Fri, 17 Apr 2020 16:46:14 +0100
Mark Rutland <mark.rutland@....com> wrote:

> > > > And doesn't BPF also do stuff like this?  
> > > 
> > > Can BPF mess with return addresses now!?  
> > 
> > At least on x86 I think it does. But what do I know, I can't operate
> > that stuff. Rostedt might know.  
> 
> Sounds like I might need to do some digging...

May want to ping Alexei. It appears that if BPF adds a direct hook to a
function, it will prevent the function graph tracer from tracing it. :-/

-- Steve