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Date:   Tue, 14 Jul 2020 12:59:34 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Arnaldo Carvalho de Melo <acme@kernel.org>
Cc:     Alexey Budankov <alexey.budankov@linux.intel.com>,
        Ravi Bangoria <ravi.bangoria@linux.ibm.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        James Morris <jmorris@namei.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Serge Hallyn <serge@hallyn.com>, Jiri Olsa <jolsa@redhat.com>,
        Song Liu <songliubraving@fb.com>,
        Andi Kleen <ak@linux.intel.com>,
        Stephane Eranian <eranian@google.com>,
        Igor Lubashev <ilubashe@akamai.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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Subject: Re: [PATCH v8 00/12] Introduce CAP_PERFMON to secure system
 performance monitoring and observability
Message-ID: <20200714105934.GU10769@hirez.programming.kicks-ass.net>
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On Mon, Jul 13, 2020 at 03:51:52PM -0300, Arnaldo Carvalho de Melo wrote:

> > > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > > index 856d98c36f56..a2397f724c10 100644
> > > --- a/kernel/events/core.c
> > > +++ b/kernel/events/core.c
> > > @@ -11595,7 +11595,7 @@ SYSCALL_DEFINE5(perf_event_open,
> > >  		 * perf_event_exit_task() that could imply).
> > >  		 */
> > >  		err = -EACCES;
> > > -		if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS))
> > > +		if (!perfmon_capable() && !ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS))
> > >  			goto err_cred;
> > >  	}
> > > 
> > >> makes monitoring simpler and even more secure to use since Perf tool need
> > >> not to start/stop/single-step and read/write registers and memory and so on
> > >> like a debugger or strace-like tool. What do you think?
> > > 
> > > I tend to agree, Peter?

So this basically says that if CAP_PERFMON, we don't care about the
ptrace() permissions? Just like how CAP_SYS_PTRACE would always allow
the ptrace checks?

I suppose that makes sense.