lkml.org 
[lkml]   [2020]   [Apr]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH v8 00/12] Introduce CAP_PERFMON to secure system performance monitoring and observability
    Em Tue, Apr 07, 2020 at 01:56:43PM -0300, Arnaldo Carvalho de Melo escreveu:
    >
    > But then, even with that attr.exclude_kernel set to 1 we _still_ get
    > kernel samples, which looks like another bug, now trying with strace,
    > which leads us to another rabbit hole:
    >
    > [perf@five ~]$ strace -e perf_event_open -o /tmp/out.put perf top --stdio
    > Error:
    > You may not have permission to collect system-wide stats.
    >
    > Consider tweaking /proc/sys/kernel/perf_event_paranoid,
    > which controls use of the performance events system by
    > unprivileged users (without CAP_PERFMON or CAP_SYS_ADMIN).
    >
    > The current value is 2:
    >
    > -1: Allow use of (almost) all events by all users
    > Ignore mlock limit after perf_event_mlock_kb without CAP_IPC_LOCK
    > >= 0: Disallow ftrace function tracepoint by users without CAP_PERFMON or CAP_SYS_ADMIN
    > Disallow raw tracepoint access by users without CAP_SYS_PERFMON or CAP_SYS_ADMIN
    > >= 1: Disallow CPU event access by users without CAP_PERFMON or CAP_SYS_ADMIN
    > >= 2: Disallow kernel profiling by users without CAP_PERFMON or CAP_SYS_ADMIN
    >
    > To make this setting permanent, edit /etc/sysctl.conf too, e.g.:
    >
    > kernel.perf_event_paranoid = -1
    >
    > [perf@five ~]$
    >
    > If I remove that strace -e ... from the front, 'perf top' is back
    > working as a non-cap_sys_admin user, just with cap_perfmon.
    >

    So I couldn't figure it out so far why is that exclude_kernel is being
    set to 1, as perf-top when no event is passed defaults to this to find
    out what to use as a default event:

    perf_evlist__add_default(top.evlist)
    perf_evsel__new_cycles(true);
    struct perf_event_attr attr = {
    .type = PERF_TYPE_HARDWARE,
    .config = PERF_COUNT_HW_CPU_CYCLES,
    .exclude_kernel = !perf_event_can_profile_kernel(),
    };

    perf_event_paranoid_check(1);
    return perf_cap__capable(CAP_SYS_ADMIN) ||
    perf_cap__capable(CAP_PERFMON) ||
    perf_event_paranoid() <= max_level;


    And then that second condition should hold true, it returns true, and
    then .exclude_kernel should be set to !true -> zero.o

    Now the wallclock says I need to stop being a programmer and turn into a
    daycare provider for Pedro, cya!

    - Arnaldo

    \
     
     \ /
      Last update: 2020-04-07 19:24    [W:5.085 / U:0.016 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site