[PATCH bpf-next v2 1/2] bpf: return target info when a tracing bpf_link is queried

[PATCH bpf-next v2 1/2] bpf: return target info when a tracing bpf_link is queried

[Toke Høiland-Jørgensen]

There is currently no way to discover the target of a tracing program
attachment after the fact. Add this information to bpf_link_info and return
it when querying the bpf_link fd.

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 include/linux/bpf_verifier.h   | 9 +++++++++
 include/uapi/linux/bpf.h       | 2 ++
 kernel/bpf/syscall.c           | 3 +++
 tools/include/uapi/linux/bpf.h | 2 ++
 4 files changed, 16 insertions(+)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 51c2ffa3d901..6023a1367853 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -487,6 +487,15 @@ static inline u64 bpf_trampoline_compute_key(const struct bpf_prog *tgt_prog,
 		return ((u64)btf_obj_id(btf) << 32) | 0x80000000 | btf_id;
 }
 
+/* unpack the IDs from the key as constructed above */
+static inline void bpf_trampoline_unpack_key(u64 key, u32 *obj_id, u32 *btf_id)
+{
+	if (obj_id)
+		*obj_id = key >> 32;
+	if (btf_id)
+		*btf_id = key & 0x7FFFFFFF;
+}
+
 int bpf_check_attach_target(struct bpf_verifier_log *log,
 			    const struct bpf_prog *prog,
 			    const struct bpf_prog *tgt_prog,
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 49371eba98ba..397884396671 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5379,6 +5379,8 @@ struct bpf_link_info {
 		} raw_tracepoint;
 		struct {
 			__u32 attach_type;
+			__u32 target_obj_id; /* prog_id for PROG_EXT, otherwise btf object id */
+			__u32 target_btf_id; /* BTF type id inside the object */
 		} tracing;
 		struct {
 			__u64 cgroup_id;
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6428634da57e..fd495190115e 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2551,6 +2551,9 @@ static int bpf_tracing_link_fill_link_info(const struct bpf_link *link,
 		container_of(link, struct bpf_tracing_link, link);
 
 	info->tracing.attach_type = tr_link->attach_type;
+	bpf_trampoline_unpack_key(tr_link->trampoline->key,
+				  &info->tracing.target_obj_id,
+				  &info->tracing.target_btf_id);
 
 	return 0;
 }
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 69902603012c..1a240be873d7 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -5373,6 +5373,8 @@ struct bpf_link_info {
 		} raw_tracepoint;
 		struct {
 			__u32 attach_type;
+			__u32 target_obj_id; /* prog_id for PROG_EXT, otherwise btf object id */
+			__u32 target_btf_id; /* BTF type id inside the object */
 		} tracing;
 		struct {
 			__u64 cgroup_id;
-- 
2.31.1

[PATCH bpf-next v2 2/2] selftests/bpf: add tests for target information in bpf_link info queries

[Toke Høiland-Jørgensen]

Extend the fexit_bpf2bpf test to check that the info for the bpf_link
returned by the kernel matches the expected values.

While we're updating the test, change existing uses of CHEC() to use the
much easier to read ASSERT_*() macros.

v2:
- Convert last CHECK() call and get rid of 'duration' var
- Split ASSERT_OK_PTR() checks to two separate if statements

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 .../selftests/bpf/prog_tests/fexit_bpf2bpf.c  | 58 ++++++++++++++-----
 1 file changed, 44 insertions(+), 14 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c b/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
index 5c0448910426..63990842d20f 100644
--- a/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
+++ b/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
@@ -58,42 +58,73 @@ static void test_fexit_bpf2bpf_common(const char *obj_file,
 				      test_cb cb)
 {
 	struct bpf_object *obj = NULL, *tgt_obj;
+	__u32 retval, tgt_prog_id, info_len;
+	struct bpf_prog_info prog_info = {};
 	struct bpf_program **prog = NULL;
 	struct bpf_link **link = NULL;
-	__u32 duration = 0, retval;
 	int err, tgt_fd, i;
+	struct btf *btf;
 
 	err = bpf_prog_load(target_obj_file, BPF_PROG_TYPE_UNSPEC,
 			    &tgt_obj, &tgt_fd);
-	if (CHECK(err, "tgt_prog_load", "file %s err %d errno %d\n",
-		  target_obj_file, err, errno))
+	if (!ASSERT_OK(err, "tgt_prog_load"))
 		return;
 	DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts,
 			    .attach_prog_fd = tgt_fd,
 			   );
 
+	info_len = sizeof(prog_info);
+	err = bpf_obj_get_info_by_fd(tgt_fd, &prog_info, &info_len);
+	if (!ASSERT_OK(err, "tgt_fd_get_info"))
+		goto close_prog;
+
+	tgt_prog_id = prog_info.id;
+	btf = bpf_object__btf(tgt_obj);
+
 	link = calloc(sizeof(struct bpf_link *), prog_cnt);
+	if (!ASSERT_OK_PTR(link, "link_ptr"))
+		goto close_prog;
+
 	prog = calloc(sizeof(struct bpf_program *), prog_cnt);
-	if (CHECK(!link || !prog, "alloc_memory", "failed to alloc memory"))
+	if (!ASSERT_OK_PTR(prog, "prog_ptr"))
 		goto close_prog;
 
 	obj = bpf_object__open_file(obj_file, &opts);
-	if (CHECK(IS_ERR_OR_NULL(obj), "obj_open",
-		  "failed to open %s: %ld\n", obj_file,
-		  PTR_ERR(obj)))
+	if (!ASSERT_OK_PTR(obj, "obj_open"))
 		goto close_prog;
 
 	err = bpf_object__load(obj);
-	if (CHECK(err, "obj_load", "err %d\n", err))
+	if (!ASSERT_OK(err, "obj_load"))
 		goto close_prog;
 
 	for (i = 0; i < prog_cnt; i++) {
+		struct bpf_link_info link_info;
+		char *tgt_name;
+		__s32 btf_id;
+
+		tgt_name = strstr(prog_name[i], "/");
+		if (!ASSERT_OK_PTR(tgt_name, "tgt_name"))
+			goto close_prog;
+		btf_id = btf__find_by_name_kind(btf, tgt_name + 1, BTF_KIND_FUNC);
+
 		prog[i] = bpf_object__find_program_by_title(obj, prog_name[i]);
-		if (CHECK(!prog[i], "find_prog", "prog %s not found\n", prog_name[i]))
+		if (!ASSERT_OK_PTR(prog[i], prog_name[i]))
 			goto close_prog;
+
 		link[i] = bpf_program__attach_trace(prog[i]);
-		if (CHECK(IS_ERR(link[i]), "attach_trace", "failed to link\n"))
+		if (!ASSERT_OK_PTR(link[i], "attach_trace"))
 			goto close_prog;
+
+		info_len = sizeof(link_info);
+		memset(&link_info, 0, sizeof(link_info));
+		err = bpf_obj_get_info_by_fd(bpf_link__fd(link[i]),
+					     &link_info, &info_len);
+		ASSERT_OK(err, "link_fd_get_info");
+		ASSERT_EQ(link_info.tracing.attach_type,
+			  bpf_program__get_expected_attach_type(prog[i]),
+			  "link_attach_type");
+		ASSERT_EQ(link_info.tracing.target_obj_id, tgt_prog_id, "link_tgt_obj_id");
+		ASSERT_EQ(link_info.tracing.target_btf_id, btf_id, "link_tgt_btf_id");
 	}
 
 	if (cb) {
@@ -106,10 +137,9 @@ static void test_fexit_bpf2bpf_common(const char *obj_file,
 		goto close_prog;
 
 	err = bpf_prog_test_run(tgt_fd, 1, &pkt_v6, sizeof(pkt_v6),
-				NULL, NULL, &retval, &duration);
-	CHECK(err || retval, "ipv6",
-	      "err %d errno %d retval %d duration %d\n",
-	      err, errno, retval, duration);
+				NULL, NULL, &retval, NULL);
+	ASSERT_OK(err, "prog_run");
+	ASSERT_EQ(retval, 0, "prog_run_ret");
 
 	if (check_data_map(obj, prog_cnt, false))
 		goto close_prog;
-- 
2.31.1

Re: [PATCH bpf-next v2 1/2] bpf: return target info when a tracing bpf_link is queried

[Alexei Starovoitov]

On Tue, Apr 13, 2021 at 2:16 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> There is currently no way to discover the target of a tracing program
> attachment after the fact. Add this information to bpf_link_info and return
> it when querying the bpf_link fd.
>
> Acked-by: Andrii Nakryiko <andrii@kernel.org>
> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>

Applied. Thanks