Re: [PATCH] perfcounters: allow sysadmin to restrict non-root counting of kernel events

[Ingo Molnar <mingo@elte.hu>]

* Peter Zijlstra <peterz@infradead.org> wrote:

> On Wed, 2009-02-18 at 21:26 +1100, Paul Mackerras wrote:
> > Impact: security feature
> > 
> > This allows the sysadmin to prevent non-root users from counting
> > hardware events that occur in kernel or hypervisor mode via a sysfs file:
> > 
> > 	/sys/devices/system/cpu/perf_counters/restrict_kernel_events
> > 
> > This defaults to off (0), allowing users to count kernel and hypervisor
> > events, but if the sysadmin writes 1 to that file, any new counters
> > created by non-root users will automatically be set to ignore kernel
> > and hypervisor events.
> > 
> > This could be useful if there is a concern that allowing non-root users
> > to count kernel or hypervisor events might leak sensitive information.
> 
> I would expect it the other way around, don't allow users 
> access to kernel/hv events unless explicitly granted.

i think it's useful to make userspace developers aware of the 
kernel overhead they are causing - while still allowing policy 
settings to override that default.

Maybe the name of the control should be switched around, to 
allow_kernel_events? [with the same functional end result though 
- i.e. default-enabled]

	Ingo