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Arnaldo Carvalho de Melo authored
kernel/events/core.c has: /* * 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 */ int sysctl_perf_event_paranoid __read_mostly = 1; So, with the default being 1, a non-root user can trace his stuff: [acme@zoo ~]$ cat /proc/sys/kernel/perf_event_paranoid 1 [acme@zoo ~]$ yes > /dev/null & [1] 15338 [acme@zoo ~]$ trace -p 15338 | head -5 0.005 ( 0.005 ms): write(fd: 1</dev/null>, buf: 0x7fe6db765000, count: 4096 ) = 4096 0.045 ( 0.001 ms): write(fd: 1</dev/null>, buf: 0x7fe6db765000, count: 4096 ) = 4096 0.085 ( 0.001 ms): write(fd: 1</dev/null>, buf: 0x7fe6db765000, count: 4096 ) = 4096 0.125 ( 0.001 ms): write(fd: 1</dev/null>, buf: 0x7fe6db765000, count: 4096 ) = 4096 0.165 ( 0.001 ms): write(fd: 1</dev/null>, buf: 0x7fe6db765000, count: 4096 ) = 4096 [acme@zoo ~]$ [acme@zoo ~]$ trace --duration 1 sleep 1 1002.148 (1001.218 ms): nanosleep(rqtp: 0x7fff46c79250 ) = 0 [acme@zoo ~]$ [acme@zoo ~]$ trace -- usleep 1 | tail -5 0.905 ( 0.002 ms): brk( ) = 0x1c82000 0.910 ( 0.003 ms): brk(brk: 0x1ca3000 ) = 0x1ca3000 0.913 ( 0.001 ms): brk( ) = 0x1ca3000 0.990 ( 0.059 ms): nanosleep(rqtp: 0x7fffe31a3280 ) = 0 0.995 ( 0.000 ms): exit_group( [acme@zoo ~]$ But can't do system wide tracing: [acme@zoo ~]$ trace Error: Operation not permitted. Hint: Check /proc/sys/kernel/perf_event_paranoid setting. Hint: For system wide tracing it needs to be set to -1. Hint: The current value is 1. [acme@zoo ~]$ [acme@zoo ~]$ trace --cpu 0 Error: Operation not permitted. Hint: Check /proc/sys/kernel/perf_event_paranoid setting. Hint: For system wide tracing it needs to be set to -1. Hint: The current value is 1. [acme@zoo ~]$ If the paranoid level is >= 2, i.e. turn this perf stuff off for !root users: [acme@zoo ~]$ sudo sh -c 'echo 2 > /proc/sys/kernel/perf_event_paranoid' [acme@zoo ~]$ cat /proc/sys/kernel/perf_event_paranoid 2 [acme@zoo ~]$ [acme@zoo ~]$ trace usleep 1 Error: Permission denied. Hint: Check /proc/sys/kernel/perf_event_paranoid setting. Hint: For your workloads it needs to be <= 1 Hint: For system wide tracing it needs to be set to -1. Hint: The current value is 2. [acme@zoo ~]$ [acme@zoo ~]$ trace Error: Permission denied. Hint: Check /proc/sys/kernel/perf_event_paranoid setting. Hint: For your workloads it needs to be <= 1 Hint: For system wide tracing it needs to be set to -1. Hint: The current value is 2. [acme@zoo ~]$ [acme@zoo ~]$ trace --cpu 1 Error: Permission denied. Hint: Check /proc/sys/kernel/perf_event_paranoid setting. Hint: For your workloads it needs to be <= 1 Hint: For system wide tracing it needs to be set to -1. Hint: The current value is 2. [acme@zoo ~]$ If the user manages to get what he/she wants, convincing root not to be paranoid at all... [root@zoo ~]# echo -1 > /proc/sys/kernel/perf_event_paranoid [root@zoo ~]# cat /proc/sys/kernel/perf_event_paranoid -1 [root@zoo ~]# [acme@zoo ~]$ ps -eo user,pid,comm | grep Xorg root 729 Xorg [acme@zoo ~]$ [acme@zoo ~]$ trace -a --duration 0.001 -e \!select,ioctl,writev | grep Xorg | head -5 23.143 ( 0.003 ms): Xorg/729 setitimer(which: REAL, value: 0x7fffaadf16e0 ) = 0 23.152 ( 0.004 ms): Xorg/729 read(fd: 31, buf: 0x2544af03, count: 4096 ) = 8 23.161 ( 0.002 ms): Xorg/729 read(fd: 31, buf: 0x2544af03, count: 4096 ) = -1 EAGAIN Resource temporarily unavailable 23.175 ( 0.002 ms): Xorg/729 setitimer(which: REAL, value: 0x7fffaadf16e0 ) = 0 23.235 ( 0.002 ms): Xorg/729 setitimer(which: REAL, value: 0x7fffaadf16e0 ) = 0 [acme@zoo ~]$ Cc: Adrian Hunter <adrian.hunter@intel.com> Cc: David Ahern <dsahern@gmail.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Mike Galbraith <efault@gmx.de> Cc: Paul Mackerras <paulus@samba.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephane Eranian <eranian@google.com> Link: http://lkml.kernel.org/n/tip-di28olfwd28rvkox7v3hqhu1@git.kernel.orgSigned-off-by:Arnaldo Carvalho de Melo <acme@redhat.com>
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