Merge branch 'Attach a cookie to a tracing program.'

Kui-Feng Lee says:

====================

Allow users to attach a 64-bits cookie to a bpf_link of fentry, fexit,
or fmod_ret.

This patchset includes several major changes.

 - Define struct bpf_tramp_links to replace bpf_tramp_prog.
   struct bpf_tramp_links collects bpf_links of a trampoline

 - Generate a trampoline to call bpf_progs of given bpf_links.

 - Trampolines always set/reset bpf_run_ctx before/after
   calling/leaving a tracing program.

 - Attach a cookie to a bpf_link of fentry/fexit/fmod_ret/lsm.  The
   value will be available when running the associated bpf_prog.

Th major differences from v6:

 - bpf_link_create() can create links of BPF_LSM_MAC attach type.

 - Add a test for lsm.

 - Add function proto of bpf_get_attach_cookie() for lsm.

 - Check BPF_LSM_MAC in bpf_prog_has_trampoline().

 - Adapt to the changes of LINK_CREATE made by Andrii.

The major differences from v7:

 - Change stack_size instead of pushing/popping run_ctx.

 - Move cookie to bpf_tramp_link from bpf_tracing_link..

v1: https://lore.kernel.org/all/20220126214809.3868787-1-kuifeng@fb.com/
v2: https://lore.kernel.org/bpf/20220316004231.1103318-1-kuifeng@fb.com/
v3: https://lore.kernel.org/bpf/20220407192552.2343076-1-kuifeng@fb.com/
v4: https://lore.kernel.org/bpf/20220411173429.4139609-1-kuifeng@fb.com/
v5: https://lore.kernel.org/bpf/20220412165555.4146407-1-kuifeng@fb.com/
v6: https://lore.kernel.org/bpf/20220416042940.656344-1-kuifeng@fb.com/
v7: https://lore.kernel.org/bpf/20220508032117.2783209-1-kuifeng@fb.com/
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

5 files changed, 40 insertions, 4 deletions

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index a9d292c106c2..5660268e103f 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -863,6 +863,14 @@ int bpf_link_create(int prog_fd, int target_fd,
 		if (!OPTS_ZEROED(opts, kprobe_multi))
 			return libbpf_err(-EINVAL);
 		break;
+	case BPF_TRACE_FENTRY:
+	case BPF_TRACE_FEXIT:
+	case BPF_MODIFY_RETURN:
+	case BPF_LSM_MAC:
+		attr.link_create.tracing.cookie = OPTS_GET(opts, tracing.cookie, 0);
+		if (!OPTS_ZEROED(opts, tracing))
+			return libbpf_err(-EINVAL);
+		break;
 	default:
 		if (!OPTS_ZEROED(opts, flags))
 			return libbpf_err(-EINVAL);
diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
index f4b4afb6d4ba..34af2232928c 100644
--- a/tools/lib/bpf/bpf.h
+++ b/tools/lib/bpf/bpf.h
@@ -420,6 +420,9 @@ struct bpf_link_create_opts {
 			const unsigned long *addrs;
 			const __u64 *cookies;
 		} kprobe_multi;
+		struct {
+			__u64 cookie;
+		} tracing;
 	};
 	size_t :0;
 };
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 15117b9a4d1e..a5904c0ac794 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -11568,12 +11568,17 @@ static int attach_raw_tp(const struct bpf_program *prog, long cookie, struct bpf
 }
 
 /* Common logic for all BPF program types that attach to a btf_id */
-static struct bpf_link *bpf_program__attach_btf_id(const struct bpf_program *prog)
+static struct bpf_link *bpf_program__attach_btf_id(const struct bpf_program *prog,
+						   const struct bpf_trace_opts *opts)
 {
+	LIBBPF_OPTS(bpf_link_create_opts, link_opts);
 	char errmsg[STRERR_BUFSIZE];
 	struct bpf_link *link;
 	int prog_fd, pfd;
 
+	if (!OPTS_VALID(opts, bpf_trace_opts))
+		return libbpf_err_ptr(-EINVAL);
+
 	prog_fd = bpf_program__fd(prog);
 	if (prog_fd < 0) {
 		pr_warn("prog '%s': can't attach before loaded\n", prog->name);
@@ -11586,7 +11591,8 @@ static struct bpf_link *bpf_program__attach_btf_id(const struct bpf_program *pro
 	link->detach = &bpf_link__detach_fd;
 
 	/* libbpf is smart enough to redirect to BPF_RAW_TRACEPOINT_OPEN on old kernels */
-	pfd = bpf_link_create(prog_fd, 0, bpf_program__expected_attach_type(prog), NULL);
+	link_opts.tracing.cookie = OPTS_GET(opts, cookie, 0);
+	pfd = bpf_link_create(prog_fd, 0, bpf_program__expected_attach_type(prog), &link_opts);
 	if (pfd < 0) {
 		pfd = -errno;
 		free(link);
@@ -11600,12 +11606,18 @@ static struct bpf_link *bpf_program__attach_btf_id(const struct bpf_program *pro
 
 struct bpf_link *bpf_program__attach_trace(const struct bpf_program *prog)
 {
-	return bpf_program__attach_btf_id(prog);
+	return bpf_program__attach_btf_id(prog, NULL);
+}
+
+struct bpf_link *bpf_program__attach_trace_opts(const struct bpf_program *prog,
+						const struct bpf_trace_opts *opts)
+{
+	return bpf_program__attach_btf_id(prog, opts);
 }
 
 struct bpf_link *bpf_program__attach_lsm(const struct bpf_program *prog)
 {
-	return bpf_program__attach_btf_id(prog);
+	return bpf_program__attach_btf_id(prog, NULL);
 }
 
 static int attach_trace(const struct bpf_program *prog, long cookie, struct bpf_link **link)
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 114b1f6f73a5..a1fb91810378 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -603,9 +603,21 @@ bpf_program__attach_tracepoint_opts(const struct bpf_program *prog,
 LIBBPF_API struct bpf_link *
 bpf_program__attach_raw_tracepoint(const struct bpf_program *prog,
 				   const char *tp_name);
+
+struct bpf_trace_opts {
+	/* size of this struct, for forward/backward compatibility */
+	size_t sz;
+	/* custom user-provided value fetchable through bpf_get_attach_cookie() */
+	__u64 cookie;
+};
+#define bpf_trace_opts__last_field cookie
+
 LIBBPF_API struct bpf_link *
 bpf_program__attach_trace(const struct bpf_program *prog);
 LIBBPF_API struct bpf_link *
+bpf_program__attach_trace_opts(const struct bpf_program *prog, const struct bpf_trace_opts *opts);
+
+LIBBPF_API struct bpf_link *
 bpf_program__attach_lsm(const struct bpf_program *prog);
 LIBBPF_API struct bpf_link *
 bpf_program__attach_cgroup(const struct bpf_program *prog, int cgroup_fd);
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index b5bc84039407..80819e26a976 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -447,6 +447,7 @@ LIBBPF_0.8.0 {
 		bpf_object__destroy_subskeleton;
 		bpf_object__open_subskeleton;
 		bpf_program__attach_kprobe_multi_opts;
+		bpf_program__attach_trace_opts;
 		bpf_program__attach_usdt;
 		libbpf_register_prog_handler;
 		libbpf_unregister_prog_handler;