Thanks for reviewing this patch. My responses below:
Michael Ellerman <mpe(a)ellerman.id.au> writes:
Vaibhav Jain <vaibhav(a)linux.ibm.com> writes:
> The newly introduced 'perf_stats' attribute uses the default access
> mode of 0444 letting non-root users access performance stats of an
> nvdimm and potentially force the kernel into issuing large number of
> expensive HCALLs. Since the information exposed by this attribute
> cannot be cached hence its better to ward of access to this attribute
> from non-root users.
> Hence this patch updates the access-mode of 'perf_stats' sysfs
> attribute file to 0400 to make it only readable to root-users.
Or should we ratelimit it?
Ideal consumers of this data will be users with
CAP_SYS_ADMIN. Also they need up-to-date values for these performance stats
as these values can be time sensitive.
So rate limiting may not be a complete solution since a user running
'perf' might be throttled by another user who is simply reading the
sysfs file contents.
So instead of setting attribute mode to 0400, will add a check for
'perfmon_capable()' in perf_stats_show() denying read access to users
without CAP_PERFMON or CAP_SYS_ADMIN.
Right. I will add this in v2.
> Reported-by: Aneesh Kumar K.V <aneesh.kumar(a)linux.ibm.com>
> Signed-off-by: Vaibhav Jain <vaibhav(a)linux.ibm.com>