Re: [PATCH v2 3/4] perf tool: make Perf tool aware of SELinux access control

[Arnaldo Carvalho de Melo]

Em Wed, Apr 22, 2020 at 05:45:34PM +0300, Alexey Budankov escreveu:
> 
> Implement SELinux sysfs check to see if the system is in enforcing
> mode and print warning message with pointers to check audit logs.
> 
> Signed-off-by: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx>
> ---
>  tools/perf/util/cloexec.c |  4 ++--
>  tools/perf/util/evsel.c   | 40 +++++++++++++++++++++++----------------
>  2 files changed, 26 insertions(+), 18 deletions(-)
> 
> diff --git a/tools/perf/util/cloexec.c b/tools/perf/util/cloexec.c
> index a12872f2856a..9c8ec816261b 100644
> --- a/tools/perf/util/cloexec.c
> +++ b/tools/perf/util/cloexec.c
> @@ -65,7 +65,7 @@ static int perf_flag_probe(void)
>  		return 1;
>  	}
>  
> -	WARN_ONCE(err != EINVAL && err != EBUSY,
> +	WARN_ONCE(err != EINVAL && err != EBUSY && err != EACCES,
>  		  "perf_event_open(..., PERF_FLAG_FD_CLOEXEC) failed with unexpected error %d (%s)\n",
>  		  err, str_error_r(err, sbuf, sizeof(sbuf)));
>  
> @@ -83,7 +83,7 @@ static int perf_flag_probe(void)
>  	if (fd >= 0)
>  		close(fd);
>  
> -	if (WARN_ONCE(fd < 0 && err != EBUSY,
> +	if (WARN_ONCE(fd < 0 && err != EBUSY && err != EACCES,
>  		      "perf_event_open(..., 0) failed unexpectedly with error %d (%s)\n",
>  		      err, str_error_r(err, sbuf, sizeof(sbuf))))
>  		return -1;
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 9fa92649adb4..82492ca12405 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -2514,32 +2514,40 @@ int perf_evsel__open_strerror(struct evsel *evsel, struct target *target,
>  			      int err, char *msg, size_t size)
>  {
>  	char sbuf[STRERR_BUFSIZE];
> -	int printed = 0;
> +	int printed = 0, enforced = 0;
>  
>  	switch (err) {
>  	case EPERM:
>  	case EACCES:
> +		printed += scnprintf(msg + printed, size - printed,
> +			"Access to performance monitoring and observability operations is limited.\n");
> +
> +		if (!sysfs__read_int("fs/selinux/enforce", &enforced)) {
> +			if (enforced) {
> +				printed += scnprintf(msg + printed, size - printed,
> +					"Enforced MAC policy settings (SELinux) can limit access to performance\n"
> +					"monitoring and observability operations. Inspect system audit records for\n"
> +					"more perf_event access control information and adjusting the policy.\n");
> +			}
> +		}
> +
>  		if (err == EPERM)
> -			printed = scnprintf(msg, size,
> -				"No permission to enable %s event.\n\n",
> +			printed += scnprintf(msg, size,
> +				"No permission to enable %s event.\n",
>  				perf_evsel__name(evsel));

This removal of a newline doesn't seem necessary to this patch.
  
>  		return scnprintf(msg + printed, size - printed,
> -		 "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_PERFMON or CAP_SYS_ADMIN).\n\n"
> -		 "The current value is %d:\n\n"
> +		 "Consider adjusting /proc/sys/kernel/perf_event_paranoid setting to open\n"
> +		 "access to performance monitoring and observability operations for users\n"
> +		 "without CAP_PERFMON capability. perf_event_paranoid setting is %d:\n"

Here we need as well to check if the kernel/libcap supports CAP_PERFMON
to provide a better error message.

>  		 "  -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_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 " : "",
> -				 perf_event_paranoid());
> +		 ">= 0: Disallow raw and ftrace function tracepoint access\n"
> +		 ">= 1: Disallow CPU event access\n"
> +		 ">= 2: Disallow kernel profiling\n"
> +		 "To make the adjusted perf_event_paranoid setting permanent preserve it\n"
> +		 "in /etc/sysctl.conf (e.g. kernel.perf_event_paranoid = <setting>)",
> +		 perf_event_paranoid());
>  	case ENOENT:
>  		return scnprintf(msg, size, "The %s event is not supported.",
>  				 perf_evsel__name(evsel));
> -- 
> 2.24.1
> 
> 

-- 

- Arnaldo