[PATCH bpf-next 0/3] bpf: Show precise rejected function when attaching to __noreturn and __btf_id functions

[PATCH bpf-next 0/3] bpf: Show precise rejected function when attaching to __noreturn and __btf_id functions

[KaFai Wan]

Show precise rejected function name when attaching to __noreturn and 
__btf_id functions.
Add selftest for attaching tracing to __btf_id functions.

---
KaFai Wan (3):
  bpf: Show precise rejected function when attaching to __noreturn
    functions
  bpf: Show precise rejected function when attaching to __btf_id
    functions
  selftests/bpf: Add selftest for attaching tracing to __btf_id
    functions

 kernel/bpf/verifier.c                            |  5 ++++-
 .../selftests/bpf/prog_tests/tracing_btf_ids.c   | 16 ++++++++++++++++
 .../selftests/bpf/progs/fexit_noreturns.c        |  2 +-
 .../selftests/bpf/progs/tracing_btf_ids.c        | 15 +++++++++++++++
 4 files changed, 36 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/tracing_btf_ids.c
 create mode 100644 tools/testing/selftests/bpf/progs/tracing_btf_ids.c

-- 
2.43.0

[PATCH bpf-next 1/3] bpf: Show precise rejected function when attaching to __noreturn functions

[KaFai Wan]

Show the precise rejected function name when attaching fexit/fmod_ret
to __noreturn functions.

$ ./fexit
libbpf: prog 'fexit': BPF program load failed: -EINVAL
libbpf: prog 'fexit': -- BEGIN PROG LOAD LOG --
Attaching fexit/fmod_ret to __noreturn function 'do_exit' is rejected.

Signed-off-by: KaFai Wan <mannkafai@gmail.com>
---
 kernel/bpf/verifier.c                               | 3 ++-
 tools/testing/selftests/bpf/progs/fexit_noreturns.c | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 53007182b46b..275d82fb1a1a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -23942,7 +23942,8 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
 	} else if ((prog->expected_attach_type == BPF_TRACE_FEXIT ||
 		   prog->expected_attach_type == BPF_MODIFY_RETURN) &&
 		   btf_id_set_contains(&noreturn_deny, btf_id)) {
-		verbose(env, "Attaching fexit/fmod_ret to __noreturn functions is rejected.\n");
+		verbose(env, "Attaching fexit/fmod_ret to __noreturn function '%s' is rejected.\n",
+			tgt_info.tgt_name);
 		return -EINVAL;
 	}
 
diff --git a/tools/testing/selftests/bpf/progs/fexit_noreturns.c b/tools/testing/selftests/bpf/progs/fexit_noreturns.c
index 54654539f550..b1c33d958ae2 100644
--- a/tools/testing/selftests/bpf/progs/fexit_noreturns.c
+++ b/tools/testing/selftests/bpf/progs/fexit_noreturns.c
@@ -8,7 +8,7 @@
 char _license[] SEC("license") = "GPL";
 
 SEC("fexit/do_exit")
-__failure __msg("Attaching fexit/fmod_ret to __noreturn functions is rejected.")
+__failure __msg("Attaching fexit/fmod_ret to __noreturn function 'do_exit' is rejected.")
 int BPF_PROG(noreturns)
 {
 	return 0;
-- 
2.43.0

[PATCH bpf-next 2/3] bpf: Show precise rejected function when attaching to __btf_id functions

[KaFai Wan]

Show the precise rejected function name when attaching tracing to
__btf_id functions.

$ ./fentry
libbpf: prog 'migrate_disable': BPF program load failed: -EINVAL
libbpf: prog 'migrate_disable': -- BEGIN PROG LOAD LOG --
Attaching tracing to __btf_id function 'migrate_disable' is rejected.

Signed-off-by: KaFai Wan <mannkafai@gmail.com>
---
 kernel/bpf/verifier.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 275d82fb1a1a..2779d63e1f8b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -23938,6 +23938,8 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
 			return ret;
 	} else if (prog->type == BPF_PROG_TYPE_TRACING &&
 		   btf_id_set_contains(&btf_id_deny, btf_id)) {
+		verbose(env, "Attaching tracing to __btf_id function '%s' is rejected.\n",
+			tgt_info.tgt_name);
 		return -EINVAL;
 	} else if ((prog->expected_attach_type == BPF_TRACE_FEXIT ||
 		   prog->expected_attach_type == BPF_MODIFY_RETURN) &&
-- 
2.43.0

Re: [PATCH bpf-next 2/3] bpf: Show precise rejected function when attaching to __btf_id functions

[Alexei Starovoitov]

On Thu, Jul 10, 2025 at 9:27 AM KaFai Wan <mannkafai@gmail.com> wrote:
>
> Show the precise rejected function name when attaching tracing to
> __btf_id functions.
>
> $ ./fentry
> libbpf: prog 'migrate_disable': BPF program load failed: -EINVAL
> libbpf: prog 'migrate_disable': -- BEGIN PROG LOAD LOG --
> Attaching tracing to __btf_id function 'migrate_disable' is rejected.
>
> Signed-off-by: KaFai Wan <mannkafai@gmail.com>
> ---
>  kernel/bpf/verifier.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 275d82fb1a1a..2779d63e1f8b 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -23938,6 +23938,8 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
>                         return ret;
>         } else if (prog->type == BPF_PROG_TYPE_TRACING &&
>                    btf_id_set_contains(&btf_id_deny, btf_id)) {
> +               verbose(env, "Attaching tracing to __btf_id function '%s' is rejected.\n",
> +                       tgt_info.tgt_name);

"Attaching tracing to __btf_id" ?! What does it mean?
Drop "__btf_id" and "tracing" bits.

--
pw-bot: cr

Re: [PATCH bpf-next 2/3] bpf: Show precise rejected function when attaching to __btf_id functions

[Yafang Shao]

On Fri, Jul 11, 2025 at 1:19 AM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Thu, Jul 10, 2025 at 9:27 AM KaFai Wan <mannkafai@gmail.com> wrote:
> >
> > Show the precise rejected function name when attaching tracing to
> > __btf_id functions.
> >
> > $ ./fentry
> > libbpf: prog 'migrate_disable': BPF program load failed: -EINVAL
> > libbpf: prog 'migrate_disable': -- BEGIN PROG LOAD LOG --
> > Attaching tracing to __btf_id function 'migrate_disable' is rejected.
> >
> > Signed-off-by: KaFai Wan <mannkafai@gmail.com>
> > ---
> >  kernel/bpf/verifier.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 275d82fb1a1a..2779d63e1f8b 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -23938,6 +23938,8 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
> >                         return ret;
> >         } else if (prog->type == BPF_PROG_TYPE_TRACING &&
> >                    btf_id_set_contains(&btf_id_deny, btf_id)) {
> > +               verbose(env, "Attaching tracing to __btf_id function '%s' is rejected.\n",
> > +                       tgt_info.tgt_name);
>
> "Attaching tracing to __btf_id" ?! What does it mean?

The term "tracing" refers to BPF_PROG_TYPE_TRACING. I believe it is
useful because it helps identify which functions cannot be attached by
a given BPF program type.
Perhaps we should replace "tracing" with "a tracing prog" for clarity?

> Drop "__btf_id" and "tracing" bits.

-- 
Regards
Yafang

Re: [PATCH bpf-next 2/3] bpf: Show precise rejected function when attaching to __btf_id functions

[KaFai Wan]

On Fri, 2025-07-11 at 17:57 +0800, Yafang Shao wrote:
> On Fri, Jul 11, 2025 at 1:19 AM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> > 
> > On Thu, Jul 10, 2025 at 9:27 AM KaFai Wan <mannkafai@gmail.com>
> > wrote:
> > > 
> > > Show the precise rejected function name when attaching tracing to
> > > __btf_id functions.
> > > 
> > > $ ./fentry
> > > libbpf: prog 'migrate_disable': BPF program load failed: -EINVAL
> > > libbpf: prog 'migrate_disable': -- BEGIN PROG LOAD LOG --
> > > Attaching tracing to __btf_id function 'migrate_disable' is
> > > rejected.
> > > 
> > > Signed-off-by: KaFai Wan <mannkafai@gmail.com>
> > > ---
> > >  kernel/bpf/verifier.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > > 
> > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > > index 275d82fb1a1a..2779d63e1f8b 100644
> > > --- a/kernel/bpf/verifier.c
> > > +++ b/kernel/bpf/verifier.c
> > > @@ -23938,6 +23938,8 @@ static int check_attach_btf_id(struct
> > > bpf_verifier_env *env)
> > >                         return ret;
> > >         } else if (prog->type == BPF_PROG_TYPE_TRACING &&
> > >                    btf_id_set_contains(&btf_id_deny, btf_id)) {
> > > +               verbose(env, "Attaching tracing to __btf_id
> > > function '%s' is rejected.\n",
> > > +                       tgt_info.tgt_name);
> > 
> > "Attaching tracing to __btf_id" ?! What does it mean?
> 
> The term "tracing" refers to BPF_PROG_TYPE_TRACING. I believe it is
> useful because it helps identify which functions cannot be attached
> by
> a given BPF program type.

Thanks, this is what I want to express.

> Perhaps we should replace "tracing" with "a tracing prog" for
> clarity?

Looks good, may be 'tracing programs' could be fine.

> 
> > Drop "__btf_id" and "tracing" bits.
> 

-- 
Thanks,
KaFai

Re: [PATCH bpf-next 2/3] bpf: Show precise rejected function when attaching to __btf_id functions

[KaFai Wan]

On Thu, 2025-07-10 at 10:19 -0700, Alexei Starovoitov wrote:
> On Thu, Jul 10, 2025 at 9:27 AM KaFai Wan <mannkafai@gmail.com>
> wrote:
> > 
> > Show the precise rejected function name when attaching tracing to
> > __btf_id functions.
> > 
> > $ ./fentry
> > libbpf: prog 'migrate_disable': BPF program load failed: -EINVAL
> > libbpf: prog 'migrate_disable': -- BEGIN PROG LOAD LOG --
> > Attaching tracing to __btf_id function 'migrate_disable' is
> > rejected.
> > 
> > Signed-off-by: KaFai Wan <mannkafai@gmail.com>
> > ---
> >  kernel/bpf/verifier.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 275d82fb1a1a..2779d63e1f8b 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -23938,6 +23938,8 @@ static int check_attach_btf_id(struct
> > bpf_verifier_env *env)
> >                         return ret;
> >         } else if (prog->type == BPF_PROG_TYPE_TRACING &&
> >                    btf_id_set_contains(&btf_id_deny, btf_id)) {
> > +               verbose(env, "Attaching tracing to __btf_id
> > function '%s' is rejected.\n",
> > +                       tgt_info.tgt_name);
> 
> "Attaching tracing to __btf_id" ?! What does it mean?
> Drop "__btf_id" and "tracing" bits.
> 

My fault, I mean "Attaching tracing programs to function" in
'btf_id_deny'.

I will change it in v2.

> --
> pw-bot: cr

-- 
Thanks,
KaFai

[PATCH bpf-next 3/3] selftests/bpf: Add selftest for attaching tracing to __btf_id functions

[KaFai Wan]

The reuslt:

  $ tools/testing/selftests/bpf/test_progs --name=tracing_btf_ids
  #467/1   tracing_btf_ids/btf_ids:OK
  #467     tracing_btf_ids:OK
  Summary: 1/1 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: KaFai Wan <mannkafai@gmail.com>
---
 .../selftests/bpf/prog_tests/tracing_btf_ids.c   | 16 ++++++++++++++++
 .../selftests/bpf/progs/tracing_btf_ids.c        | 15 +++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/tracing_btf_ids.c
 create mode 100644 tools/testing/selftests/bpf/progs/tracing_btf_ids.c

diff --git a/tools/testing/selftests/bpf/prog_tests/tracing_btf_ids.c b/tools/testing/selftests/bpf/prog_tests/tracing_btf_ids.c
new file mode 100644
index 000000000000..b45b9ac3630c
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/tracing_btf_ids.c
@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <test_progs.h>
+#include "tracing_btf_ids.skel.h"
+
+void test_tracing_btf_ids(void)
+{
+	int btf_id;
+
+	// `migrate_disable` depends on `CONFIG_SMP`, may not exists
+	btf_id = libbpf_find_vmlinux_btf_id("migrate_disable", BPF_TRACE_FENTRY);
+	if (btf_id <= 0)
+		return;
+
+	RUN_TESTS(tracing_btf_ids);
+}
diff --git a/tools/testing/selftests/bpf/progs/tracing_btf_ids.c b/tools/testing/selftests/bpf/progs/tracing_btf_ids.c
new file mode 100644
index 000000000000..92a7f2e9fb89
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/tracing_btf_ids.c
@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_misc.h"
+
+char _license[] SEC("license") = "GPL";
+
+SEC("fentry/migrate_disable")
+__failure __msg("Attaching tracing to __btf_id function 'migrate_disable' is rejected.")
+int BPF_PROG(btf_ids)
+{
+	return 0;
+}
-- 
2.43.0