[PATCH v8 00/12] Introduce CAP_PERFMON to secure system performance monitoring and observability
Arnaldo Carvalho de Melo
arnaldo.melo at gmail.com
Tue Apr 7 16:56:43 UTC 2020
Em Tue, Apr 07, 2020 at 01:36:54PM -0300, Arnaldo Carvalho de Melo escreveu:
> 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 :-\
So running with 'perf top --stdio -vv 2> /tmp/output' I see we try
create three events, the first is some capability querying, then we try
to determine the max precision level, but continue with
attr.exclude_kernel=1, which shouldn't be the case, perhaps we're seeing
that it is not the root in the tooling part, and end up setting that to
1 as, previously, we knew it would fail, so we should switch to checking
if we have cap_perfmon too, will check that:
------------------------------------------------------------
perf_event_attr:
type 1
size 120
config 0x9
watermark 1
sample_id_all 1
bpf_event 1
{ wakeup_events, wakeup_watermark } 1
------------------------------------------------------------
------------------------------------------------------------
perf_event_attr:
size 120
{ sample_period, sample_freq } 4000
sample_type IP|TID|TIME|CPU|PERIOD
read_format ID
disabled 1
inherit 1
exclude_kernel 1
mmap 1
comm 1
freq 1
task 1
precise_ip 3
sample_id_all 1
exclude_guest 1
mmap2 1
comm_exec 1
ksymbol 1
bpf_event 1
------------------------------------------------------------
------------------------------------------------------------
perf_event_attr:
size 120
{ sample_period, sample_freq } 4000
sample_type IP|TID|TIME|CPU|PERIOD
read_format ID
disabled 1
inherit 1
exclude_kernel 1
mmap 1
comm 1
freq 1
task 1
precise_ip 2
sample_id_all 1
exclude_guest 1
mmap2 1
comm_exec 1
ksymbol 1
bpf_event 1
------------------------------------------------------------
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 at 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 at 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.
- Arnaldo
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