On Thu, Apr 02, 2020 at 11:47:35AM +0300, Alexey Budankov wrote:
>
> Extend error messages to mention CAP_PERFMON capability as an option
> to substitute CAP_SYS_ADMIN capability for secure system performance
> monitoring and observability operations. Make perf_event_paranoid_check()
> and __cmd_ftrace() to be aware of CAP_PERFMON capability.
>
> CAP_PERFMON implements the principal of least privilege for performance
> monitoring and observability operations (POSIX IEEE 1003.1e 2.2.2.39
> principle of least privilege: A security design principle that states
> that a process or program be granted only those privileges (e.g.,
> capabilities) necessary to accomplish its legitimate function, and only
> for the time that such privileges are actually required)
>
> For backward compatibility reasons access to perf_events subsystem remains
> open for CAP_SYS_ADMIN privileged processes but CAP_SYS_ADMIN usage for
> secure perf_events monitoring is discouraged with respect to CAP_PERFMON
> capability.
>
> Signed-off-by: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx>
> Reviewed-by: James Morris <jamorris@xxxxxxxxxxxxxxxxxxx>
Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
thanks,
jirka
> ---
> tools/perf/builtin-ftrace.c | 5 +++--
> tools/perf/design.txt | 3 ++-
> tools/perf/util/cap.h | 4 ++++
> tools/perf/util/evsel.c | 10 +++++-----
> tools/perf/util/util.c | 1 +
> 5 files changed, 15 insertions(+), 8 deletions(-)
>
> diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
> index d5adc417a4ca..55eda54240fb 100644
> --- a/tools/perf/builtin-ftrace.c
> +++ b/tools/perf/builtin-ftrace.c
> @@ -284,10 +284,11 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
> .events = POLLIN,
> };
>
> - if (!perf_cap__capable(CAP_SYS_ADMIN)) {
> + if (!(perf_cap__capable(CAP_PERFMON) ||
> + perf_cap__capable(CAP_SYS_ADMIN))) {
> pr_err("ftrace only works for %s!\n",
> #ifdef HAVE_LIBCAP_SUPPORT
> - "users with the SYS_ADMIN capability"
> + "users with the CAP_PERFMON or CAP_SYS_ADMIN capability"
> #else
> "root"
> #endif
> diff --git a/tools/perf/design.txt b/tools/perf/design.txt
> index 0453ba26cdbd..a42fab308ff6 100644
> --- a/tools/perf/design.txt
> +++ b/tools/perf/design.txt
> @@ -258,7 +258,8 @@ gets schedule to. Per task counters can be created by any user, for
> their own tasks.
>
> A 'pid == -1' and 'cpu == x' counter is a per CPU counter that counts
> -all events on CPU-x. Per CPU counters need CAP_SYS_ADMIN privilege.
> +all events on CPU-x. Per CPU counters need CAP_PERFMON or CAP_SYS_ADMIN
> +privilege.
>
> The 'flags' parameter is currently unused and must be zero.
>
> diff --git a/tools/perf/util/cap.h b/tools/perf/util/cap.h
> index 051dc590ceee..ae52878c0b2e 100644
> --- a/tools/perf/util/cap.h
> +++ b/tools/perf/util/cap.h
> @@ -29,4 +29,8 @@ static inline bool perf_cap__capable(int cap __maybe_unused)
> #define CAP_SYSLOG 34
> #endif
>
> +#ifndef CAP_PERFMON
> +#define CAP_PERFMON 38
> +#endif
> +
> #endif /* __PERF_CAP_H */
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 816d930d774e..2696922f06bc 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -2507,14 +2507,14 @@ int perf_evsel__open_strerror(struct evsel *evsel, struct target *target,
> "You may not have permission to collect %sstats.\n\n"
> "Consider tweaking /proc/sys/kernel/perf_event_paranoid,\n"
> "which controls use of the performance events system by\n"
> - "unprivileged users (without CAP_SYS_ADMIN).\n\n"
> + "unprivileged users (without CAP_PERFMON or CAP_SYS_ADMIN).\n\n"
> "The current value is %d:\n\n"
> " -1: Allow use of (almost) all events by all users\n"
> " Ignore mlock limit after perf_event_mlock_kb without CAP_IPC_LOCK\n"
> - ">= 0: Disallow ftrace function tracepoint by users without CAP_SYS_ADMIN\n"
> - " Disallow raw tracepoint access by users without CAP_SYS_ADMIN\n"
> - ">= 1: Disallow CPU event access by users without CAP_SYS_ADMIN\n"
> - ">= 2: Disallow kernel profiling by users without CAP_SYS_ADMIN\n\n"
> + ">= 0: Disallow ftrace function tracepoint by users without CAP_PERFMON or CAP_SYS_ADMIN\n"
> + " Disallow raw tracepoint access by users without CAP_SYS_PERFMON or CAP_SYS_ADMIN\n"
> + ">= 1: Disallow CPU event access by users without CAP_PERFMON or CAP_SYS_ADMIN\n"
> + ">= 2: Disallow kernel profiling by users without CAP_PERFMON or CAP_SYS_ADMIN\n\n"
> "To make this setting permanent, edit /etc/sysctl.conf too, e.g.:\n\n"
> " kernel.perf_event_paranoid = -1\n" ,
> target->system_wide ? "system-wide " : "",
> diff --git a/tools/perf/util/util.c b/tools/perf/util/util.c
> index d707c9624dd9..37a9492edb3e 100644
> --- a/tools/perf/util/util.c
> +++ b/tools/perf/util/util.c
> @@ -290,6 +290,7 @@ int perf_event_paranoid(void)
> bool perf_event_paranoid_check(int max_level)
> {
> return perf_cap__capable(CAP_SYS_ADMIN) ||
> + perf_cap__capable(CAP_PERFMON) ||
> perf_event_paranoid() <= max_level;
> }
>
> --
> 2.24.1
>
