[PATCH v8 00/12] Introduce CAP_PERFMON to secure system performance monitoring and observability

[Arnaldo Carvalho de Melo]

Em Tue, Apr 07, 2020 at 05:54:27PM +0300, Alexey Budankov escreveu:
> On 07.04.2020 17:35, Arnaldo Carvalho de Melo wrote:
> > Em Tue, Apr 07, 2020 at 11:30:14AM -0300, Arnaldo Carvalho de Melo escreveu:
> >> [perf at five ~]$ type perf
> >> perf is hashed (/home/perf/bin/perf)
> >> [perf at five ~]$ getcap /home/perf/bin/perf
> >> /home/perf/bin/perf = cap_sys_ptrace,cap_syslog,38+ep
> >> [perf at five ~]$ groups
> >> perf perf_users
> >> [perf at five ~]$ id
> >> uid=1002(perf) gid=1002(perf) groups=1002(perf),1003(perf_users) context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
> >> [perf at five ~]$ perf top --stdio
> >> Error:
> >> Failed to mmap with 1 (Operation not permitted)
> >> [perf at five ~]$ perf record -a
> >> ^C[ perf record: Woken up 1 times to write data ]
> >> [ perf record: Captured and wrote 1.177 MB perf.data (1552 samples) ]
> >>
> >> [perf at five ~]$ perf evlist
> >> cycles:u
> >> [perf at five ~]$
> > 
> > Humm, perf record falls back to cycles:u after initially trying cycles
> > (i.e. kernel and userspace), lemme see trying 'perf top -e cycles:u',
> > lemme test, humm not really:
> > 
> > [perf at five ~]$ perf top --stdio -e cycles:u
> > Error:
> > Failed to mmap with 1 (Operation not permitted)
> > [perf at five ~]$ perf record -e cycles:u -a sleep 1
> > [ perf record: Woken up 1 times to write data ]
> > [ perf record: Captured and wrote 1.123 MB perf.data (132 samples) ]
> > [perf at five ~]$
> > 
> > Back to debugging this.
> 
> Could makes sense adding cap_ipc_lock to the binary to isolate from this:
> 
> kernel/events/core.c: 6101
> 	if ((locked > lock_limit) && perf_is_paranoid() &&
> 		!capable(CAP_IPC_LOCK)) {
> 		ret = -EPERM;
> 		goto unlock;
> 	}


That did the trick, I'll update the documentation and include in my
"Committer testing" section:

[perf at five ~]$ groups
perf perf_users
[perf at five ~]$ ls -lahF bin/perf
-rwxr-x---. 1 root perf_users 24M Apr  7 10:34 bin/perf*
[perf at five ~]$ getcap bin/perf
bin/perf = cap_ipc_lock,cap_sys_ptrace,cap_syslog,38+ep
[perf at five ~]$
[perf at five ~]$ perf top --stdio


   PerfTop:     652 irqs/sec  kernel:73.8%  exact: 99.7% lost: 0/0 drop: 0/0 [4000Hz cycles:u],  (all, 12 CPUs)
---------------------------------------------------------------------------------------------------------------

    13.03%  [kernel]               [k] module_get_kallsym
     5.25%  [kernel]               [k] kallsyms_expand_symbol.constprop.0
     5.00%  libc-2.30.so           [.] __GI_____strtoull_l_internal
     4.41%  [kernel]               [k] memcpy
     3.42%  [kernel]               [k] vsnprintf
     2.98%  perf                   [.] map__process_kallsym_symbol
     2.86%  [kernel]               [k] format_decode
     2.73%  [kernel]               [k] number
     2.70%  perf                   [.] rb_next
     2.59%  perf                   [.] maps__split_kallsyms
     2.54%  [kernel]               [k] string_nocheck
     1.90%  libc-2.30.so           [.] _IO_getdelim
     1.86%  [kernel]               [k] __x86_indirect_thunk_rax
     1.53%  libc-2.30.so           [.] _int_malloc
     1.48%  libc-2.30.so           [.] __memmove_avx_unaligned_erms
     1.40%  [kernel]               [k] clear_page_rep
     1.07%  perf                   [.] rb_insert_color
     1.01%  libc-2.30.so           [.] _IO_feof
     0.99%  perf                   [.] __dso__load_kallsyms
     0.98%  [kernel]               [k] s_next
     0.96%  perf                   [.] __rblist__findnew
     0.95%  [kernel]               [k] strlen
     0.95%  perf                   [.] arch__symbols__fixup_end
     0.94%  libpixman-1.so.0.38.4  [.] 0x000000000006f4af
     0.94%  perf                   [.] symbol__new
     0.89%  libpixman-1.so.0.38.4  [.] 0x000000000006f4a0
     0.86%  [kernel]               [k] seq_read
     0.81%  libpixman-1.so.0.38.4  [.] 0x000000000006f4ab
     0.80%  perf                   [.] __symbols__insert
     0.73%  libpixman-1.so.0.38.4  [.] 0x000000000006f4a7
     0.67%  [kernel]               [k] s_show
     0.66%  libc-2.30.so           [.] __libc_calloc
     0.61%  libpixman-1.so.0.38.4  [.] 0x000000000006f4bb
     0.59%  [kernel]               [k] get_page_from_freelist
     0.59%  perf                   [.] memcpy at plt
     0.58%  perf                   [.] eprintf
exiting.
[perf at five ~]$

There is still something strange in here, the event is cycles:u (see at
the PerfTop line, but it is getting kernel samples :-\

- Arnaldo