On Mon, August 12, 2019 at 4:16 PM Arnaldo Carvalho de Melo <arnaldo.m...@gmail.com> wrote: > Em Mon, Aug 12, 2019 at 05:01:34PM -0300, Arnaldo Carvalho de Melo > escreveu: > > Em Wed, Aug 07, 2019 at 10:44:15AM -0400, Igor Lubashev escreveu: > > > +++ b/tools/perf/util/evsel.c > > > @@ -279,7 +279,7 @@ struct evsel *perf_evsel__new_idx(struct > > > perf_event_attr *attr, int idx) > > > > > static bool perf_event_can_profile_kernel(void) > > > { > > > - return geteuid() == 0 || perf_event_paranoid() == -1; > > > + return perf_event_paranoid_check(-1); > > > } > > > > While looking at your changes I think the pre-existing code is wrong, > > i.e. the check in sys_perf_event_open(), in the kernel is: > > > > if (!attr.exclude_kernel) { > > if (perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN)) > > return -EACCES; > > } > > > > And: > > > > static inline bool perf_paranoid_kernel(void) { > > return sysctl_perf_event_paranoid > 1; } > > > > So we have to change that perf_event_paranoit_check(-1) to pass 1 > > instead?
Indeed. This seems right. It was a pre-existing problem. > > bool perf_event_paranoid_check(int max_level) { > > return perf_cap__capable(CAP_SYS_ADMIN) || > > perf_event_paranoid() <= max_level; } > > > > Also you defined perf_cap__capable(anything) as: > > > > #ifdef HAVE_LIBCAP_SUPPORT > > > > #include <sys/capability.h> > > > > bool perf_cap__capable(cap_value_t cap); > > > > #else > > > > static inline bool perf_cap__capable(int cap __maybe_unused) > > { > > return false; > > } > > > > #endif /* HAVE_LIBCAP_SUPPORT */ > > > > > > I think we should have: > > > > #else > > > > static inline bool perf_cap__capable(int cap __maybe_unused) { > > return geteuid() == 0; > > } > > > > #endif /* HAVE_LIBCAP_SUPPORT */ > > > > Right? You can have EUID==0 and not have CAP_SYS_ADMIN, though this would be rare in practice. I did not to use EUID in leu of libcap, since kernel does not do so, and therefore it seemed a bit misleading. But this is a slight matter of taste, and I do not see a problem with choosing to fall back to EUID -- the kernel will do the right thing anyway. Now, if I were pedantic, I'd say that to use geteuid(), you need to #include <unistd.h> . > > So I am removing the introduction of perf_cap__capable() from the > > first patch you sent, leaving it with _only_ the feature detection > > part, using that feature detection to do anything is then moved to a > > separate patch, after we finish this discussion about what we should > > fallback to when libcap-devel isn't available, i.e. we should use the > > previous checks, etc. > > So, please take a look at the tmp.perf/cap branch in my git repo: > > https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/log/?h=tmp.p > erf/cap > > I split the patch and made perf_cap__capable() fallback to 'return > geteuid() == 0;' when libcap-devel isn't available, i.e. keep the checks made > prior to your patchset. Thank you. And thanks for updating "make_minimal". > > Jiri, can I keep your Acked-by? > > - Arnaldo