Re: [PATCH] perf/core: Add macros for possible sysctl_perf_event_paranoid values

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Jul 08, 2022 at 10:10:15AM +0100, James Clark wrote:
> 
> 
> On 01/07/2022 07:39, Anshuman Khandual wrote:
> > sysctl_perf_event_paranoid can have values from [-1, 0, 1, 2] which decides
> > on perf event restrictions for unprivileged users. But using them directly
> > makes it difficult to correlate exact restriction level they might impose.
> > This just adds macros for those numerical restriction values, making them
> > clear and improving readability.
> > 
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Ingo Molnar <mingo@redhat.com>
> > Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
> > Cc: Mark Rutland <mark.rutland@arm.com>
> > Cc: linux-perf-users@vger.kernel.org
> > Cc: linux-kernel@vger.kernel.org
> > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> > ---
> >  include/linux/perf_event.h | 22 ++++++++++++++++++----
> >  kernel/events/core.c       |  9 +--------
> >  kernel/kallsyms.c          |  3 ++-
> >  3 files changed, 21 insertions(+), 13 deletions(-)
> > 
> > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> > index da759560eec5..78156b9154df 100644
> > --- a/include/linux/perf_event.h
> > +++ b/include/linux/perf_event.h
> > @@ -1359,14 +1359,28 @@ int perf_event_max_stack_handler(struct ctl_table *table, int write,
> >  #define PERF_SECURITY_KERNEL		2
> >  #define PERF_SECURITY_TRACEPOINT	3
> >  
> > +/*
> > + * perf event paranoia level:
> > + *  -1 - not paranoid at all
> > + *   0 - disallow raw tracepoint access for unpriv
> > + *   1 - disallow cpu events for unpriv
> > + *   2 - disallow kernel profiling for unpriv
> > + */
> > +enum {
> > +	PERF_EVENT_DISALLOW_NONE	= -1,
> > +	PERF_EVENT_DISALLOW_TRACE,
> > +	PERF_EVENT_DISALLOW_CPU,
> > +	PERF_EVENT_DISALLOW_KERNEL
> > +};
> > +
> >  static inline int perf_is_paranoid(void)
> >  {
> > -	return sysctl_perf_event_paranoid > -1;
> > +	return sysctl_perf_event_paranoid > PERF_EVENT_DISALLOW_NONE;
> >  }
> >  
> 
> Hi Anshuman,
> 
> There are quite a few other instances of integers left in the tools code.
> If you search for perf_event_paranoid_check() and perf_event_paranoid()
> you will find them.
> 
> I'm also wondering if it makes sense to return your new enum from all of
> the helper functions instead of an int and make it explicit that it's
> an instance of this new type? Although the compiler doesn't seem to warn
> about using integers so maybe it's not worth doing this.

so I don't see the point of all this; it's already wrapped in these
helper functions that have a descriptive name, why do we need more muck
on top?