* [PATCH] perf bpf-filter: Improve error messages
@ 2025-06-04 5:42 Namhyung Kim
2025-06-04 16:00 ` Ian Rogers
0 siblings, 1 reply; 2+ messages in thread
From: Namhyung Kim @ 2025-06-04 5:42 UTC (permalink / raw)
To: Arnaldo Carvalho de Melo, Ian Rogers, Kan Liang
Cc: Jiri Olsa, Adrian Hunter, Peter Zijlstra, Ingo Molnar, LKML,
linux-perf-users
The BPF filter needs libbpf/BPF-skeleton support and root privilege.
Add error messages to help users understand the problem easily.
When it's not build with BPF support (make BUILD_BPF_SKEL=0).
$ sudo perf record -e cycles --filter "pid != 0" true
Error: BPF filter is requested but perf is not built with BPF.
Please make sure to build with libbpf and BPF skeleton.
Usage: perf record [<options>] [<command>]
or: perf record [<options>] -- <command> [<options>]
--filter <filter>
event filter
When it supports BPF but runs without root or CAP_BPF. Note that it
also checks pinned BPF filters.
$ perf record -e cycles --filter "pid != 0" -o /dev/null true
Error: BPF filter only works for users with the CAP_BPF capability!
Please run 'perf record --setup-filter pin' as root first.
Usage: perf record [<options>] [<command>]
or: perf record [<options>] -- <command> [<options>]
--filter <filter>
event filter
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
tools/perf/util/bpf-filter.c | 28 ++++++++++++++++++++++++++++
tools/perf/util/bpf-filter.h | 3 +++
tools/perf/util/cap.c | 1 -
tools/perf/util/cap.h | 5 +++++
4 files changed, 36 insertions(+), 1 deletion(-)
diff --git a/tools/perf/util/bpf-filter.c b/tools/perf/util/bpf-filter.c
index a4fdf6911ec1c32e..92e2f054b45e91dd 100644
--- a/tools/perf/util/bpf-filter.c
+++ b/tools/perf/util/bpf-filter.c
@@ -52,6 +52,7 @@
#include <internal/xyarray.h>
#include <perf/threadmap.h>
+#include "util/cap.h"
#include "util/debug.h"
#include "util/evsel.h"
#include "util/target.h"
@@ -618,11 +619,38 @@ struct perf_bpf_filter_expr *perf_bpf_filter_expr__new(enum perf_bpf_filter_term
return expr;
}
+static bool check_bpf_filter_capable(void)
+{
+ bool used_root;
+
+ if (perf_cap__capable(CAP_BPF, &used_root))
+ return true;
+
+ if (!used_root) {
+ /* Check if root already pinned the filter programs and maps */
+ int fd = get_pinned_fd("filters");
+
+ if (fd >= 0) {
+ close(fd);
+ return true;
+ }
+ }
+
+ pr_err("Error: BPF filter only works for %s!\n"
+ "\tPlease run 'perf record --setup-filter pin' as root first.\n",
+ used_root ? "root" : "users with the CAP_BPF capability");
+
+ return false;
+}
+
int perf_bpf_filter__parse(struct list_head *expr_head, const char *str)
{
YY_BUFFER_STATE buffer;
int ret;
+ if (!check_bpf_filter_capable())
+ return -EPERM;
+
buffer = perf_bpf_filter__scan_string(str);
ret = perf_bpf_filter_parse(expr_head);
diff --git a/tools/perf/util/bpf-filter.h b/tools/perf/util/bpf-filter.h
index 916ed7770b734f15..187e5bbcc5910d78 100644
--- a/tools/perf/util/bpf-filter.h
+++ b/tools/perf/util/bpf-filter.h
@@ -2,6 +2,7 @@
#ifndef PERF_UTIL_BPF_FILTER_H
#define PERF_UTIL_BPF_FILTER_H
+#include <stdio.h>
#include <linux/list.h>
#include "bpf_skel/sample-filter.h"
@@ -38,6 +39,8 @@ int perf_bpf_filter__unpin(void);
static inline int perf_bpf_filter__parse(struct list_head *expr_head __maybe_unused,
const char *str __maybe_unused)
{
+ fprintf(stderr, "Error: BPF filter is requested but perf is not built with BPF.\n"
+ "\tPlease make sure to build with libbpf and BPF skeleton.\n");
return -EOPNOTSUPP;
}
static inline int perf_bpf_filter__prepare(struct evsel *evsel __maybe_unused,
diff --git a/tools/perf/util/cap.c b/tools/perf/util/cap.c
index 69d9a2bcd40bfdd1..24a0ea7e6d97749b 100644
--- a/tools/perf/util/cap.c
+++ b/tools/perf/util/cap.c
@@ -7,7 +7,6 @@
#include "debug.h"
#include <errno.h>
#include <string.h>
-#include <linux/capability.h>
#include <sys/syscall.h>
#include <unistd.h>
diff --git a/tools/perf/util/cap.h b/tools/perf/util/cap.h
index 0c6a1ff55f07340a..c1b8ac033ccc5826 100644
--- a/tools/perf/util/cap.h
+++ b/tools/perf/util/cap.h
@@ -3,6 +3,7 @@
#define __PERF_CAP_H
#include <stdbool.h>
+#include <linux/capability.h>
/* For older systems */
#ifndef CAP_SYSLOG
@@ -13,6 +14,10 @@
#define CAP_PERFMON 38
#endif
+#ifndef CAP_BPF
+#define CAP_BPF 39
+#endif
+
/* Query if a capability is supported, used_root is set if the fallback root check was used. */
bool perf_cap__capable(int cap, bool *used_root);
--
2.49.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] perf bpf-filter: Improve error messages
2025-06-04 5:42 [PATCH] perf bpf-filter: Improve error messages Namhyung Kim
@ 2025-06-04 16:00 ` Ian Rogers
0 siblings, 0 replies; 2+ messages in thread
From: Ian Rogers @ 2025-06-04 16:00 UTC (permalink / raw)
To: Namhyung Kim
Cc: Arnaldo Carvalho de Melo, Kan Liang, Jiri Olsa, Adrian Hunter,
Peter Zijlstra, Ingo Molnar, LKML, linux-perf-users
On Tue, Jun 3, 2025 at 10:42 PM Namhyung Kim <namhyung@kernel.org> wrote:
>
> The BPF filter needs libbpf/BPF-skeleton support and root privilege.
> Add error messages to help users understand the problem easily.
>
> When it's not build with BPF support (make BUILD_BPF_SKEL=0).
>
> $ sudo perf record -e cycles --filter "pid != 0" true
> Error: BPF filter is requested but perf is not built with BPF.
> Please make sure to build with libbpf and BPF skeleton.
>
> Usage: perf record [<options>] [<command>]
> or: perf record [<options>] -- <command> [<options>]
>
> --filter <filter>
> event filter
>
> When it supports BPF but runs without root or CAP_BPF. Note that it
> also checks pinned BPF filters.
>
> $ perf record -e cycles --filter "pid != 0" -o /dev/null true
> Error: BPF filter only works for users with the CAP_BPF capability!
> Please run 'perf record --setup-filter pin' as root first.
>
> Usage: perf record [<options>] [<command>]
> or: perf record [<options>] -- <command> [<options>]
>
> --filter <filter>
> event filter
>
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> ---
> tools/perf/util/bpf-filter.c | 28 ++++++++++++++++++++++++++++
> tools/perf/util/bpf-filter.h | 3 +++
> tools/perf/util/cap.c | 1 -
> tools/perf/util/cap.h | 5 +++++
> 4 files changed, 36 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/bpf-filter.c b/tools/perf/util/bpf-filter.c
> index a4fdf6911ec1c32e..92e2f054b45e91dd 100644
> --- a/tools/perf/util/bpf-filter.c
> +++ b/tools/perf/util/bpf-filter.c
> @@ -52,6 +52,7 @@
> #include <internal/xyarray.h>
> #include <perf/threadmap.h>
>
> +#include "util/cap.h"
> #include "util/debug.h"
> #include "util/evsel.h"
> #include "util/target.h"
> @@ -618,11 +619,38 @@ struct perf_bpf_filter_expr *perf_bpf_filter_expr__new(enum perf_bpf_filter_term
> return expr;
> }
>
> +static bool check_bpf_filter_capable(void)
> +{
> + bool used_root;
> +
> + if (perf_cap__capable(CAP_BPF, &used_root))
> + return true;
> +
> + if (!used_root) {
> + /* Check if root already pinned the filter programs and maps */
> + int fd = get_pinned_fd("filters");
> +
> + if (fd >= 0) {
> + close(fd);
> + return true;
> + }
> + }
> +
> + pr_err("Error: BPF filter only works for %s!\n"
> + "\tPlease run 'perf record --setup-filter pin' as root first.\n",
> + used_root ? "root" : "users with the CAP_BPF capability");
> +
> + return false;
> +}
> +
> int perf_bpf_filter__parse(struct list_head *expr_head, const char *str)
> {
> YY_BUFFER_STATE buffer;
> int ret;
>
> + if (!check_bpf_filter_capable())
> + return -EPERM;
> +
> buffer = perf_bpf_filter__scan_string(str);
>
> ret = perf_bpf_filter_parse(expr_head);
> diff --git a/tools/perf/util/bpf-filter.h b/tools/perf/util/bpf-filter.h
> index 916ed7770b734f15..187e5bbcc5910d78 100644
> --- a/tools/perf/util/bpf-filter.h
> +++ b/tools/perf/util/bpf-filter.h
> @@ -2,6 +2,7 @@
> #ifndef PERF_UTIL_BPF_FILTER_H
> #define PERF_UTIL_BPF_FILTER_H
>
> +#include <stdio.h>
> #include <linux/list.h>
>
> #include "bpf_skel/sample-filter.h"
> @@ -38,6 +39,8 @@ int perf_bpf_filter__unpin(void);
> static inline int perf_bpf_filter__parse(struct list_head *expr_head __maybe_unused,
> const char *str __maybe_unused)
> {
> + fprintf(stderr, "Error: BPF filter is requested but perf is not built with BPF.\n"
> + "\tPlease make sure to build with libbpf and BPF skeleton.\n");
Generally LGTM. This needs to be a pr_err otherwise nothing will be
displayed with TUI.
Thanks,
Ian
> return -EOPNOTSUPP;
> }
> static inline int perf_bpf_filter__prepare(struct evsel *evsel __maybe_unused,
> diff --git a/tools/perf/util/cap.c b/tools/perf/util/cap.c
> index 69d9a2bcd40bfdd1..24a0ea7e6d97749b 100644
> --- a/tools/perf/util/cap.c
> +++ b/tools/perf/util/cap.c
> @@ -7,7 +7,6 @@
> #include "debug.h"
> #include <errno.h>
> #include <string.h>
> -#include <linux/capability.h>
> #include <sys/syscall.h>
> #include <unistd.h>
>
> diff --git a/tools/perf/util/cap.h b/tools/perf/util/cap.h
> index 0c6a1ff55f07340a..c1b8ac033ccc5826 100644
> --- a/tools/perf/util/cap.h
> +++ b/tools/perf/util/cap.h
> @@ -3,6 +3,7 @@
> #define __PERF_CAP_H
>
> #include <stdbool.h>
> +#include <linux/capability.h>
>
> /* For older systems */
> #ifndef CAP_SYSLOG
> @@ -13,6 +14,10 @@
> #define CAP_PERFMON 38
> #endif
>
> +#ifndef CAP_BPF
> +#define CAP_BPF 39
> +#endif
> +
> /* Query if a capability is supported, used_root is set if the fallback root check was used. */
> bool perf_cap__capable(int cap, bool *used_root);
>
> --
> 2.49.0
>
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