bpf: add fsession support

The fsession is something that similar to kprobe session. It allow to
attach a single BPF program to both the entry and the exit of the target
functions.

Introduce the struct bpf_fsession_link, which allows to add the link to
both the fentry and fexit progs_hlist of the trampoline.

Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
Co-developed-by: Leon Hwang <leon.hwang@linux.dev>
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
Link: https://lore.kernel.org/r/20260124062008.8657-2-dongml2@chinatelecom.cn
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 45 insertions, 8 deletions

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 2a125d063e62..edf9da43762d 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -109,10 +109,17 @@ bool bpf_prog_has_trampoline(const struct bpf_prog *prog)
 	enum bpf_attach_type eatype = prog->expected_attach_type;
 	enum bpf_prog_type ptype = prog->type;
 
-	return (ptype == BPF_PROG_TYPE_TRACING &&
-		(eatype == BPF_TRACE_FENTRY || eatype == BPF_TRACE_FEXIT ||
-		 eatype == BPF_MODIFY_RETURN)) ||
-		(ptype == BPF_PROG_TYPE_LSM && eatype == BPF_LSM_MAC);
+	switch (ptype) {
+	case BPF_PROG_TYPE_TRACING:
+		if (eatype == BPF_TRACE_FENTRY || eatype == BPF_TRACE_FEXIT ||
+		    eatype == BPF_MODIFY_RETURN || eatype == BPF_TRACE_FSESSION)
+			return true;
+		return false;
+	case BPF_PROG_TYPE_LSM:
+		return eatype == BPF_LSM_MAC;
+	default:
+		return false;
+	}
 }
 
 void bpf_image_ksym_init(void *data, unsigned int size, struct bpf_ksym *ksym)
@@ -559,6 +566,8 @@ static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(struct bpf_prog *prog)
 		return BPF_TRAMP_MODIFY_RETURN;
 	case BPF_TRACE_FEXIT:
 		return BPF_TRAMP_FEXIT;
+	case BPF_TRACE_FSESSION:
+		return BPF_TRAMP_FSESSION;
 	case BPF_LSM_MAC:
 		if (!prog->aux->attach_func_proto->type)
 			/* The function returns void, we cannot modify its
@@ -594,8 +603,10 @@ static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link,
 				      struct bpf_trampoline *tr,
 				      struct bpf_prog *tgt_prog)
 {
+	struct bpf_fsession_link *fslink = NULL;
 	enum bpf_tramp_prog_type kind;
 	struct bpf_tramp_link *link_exiting;
+	struct hlist_head *prog_list;
 	int err = 0;
 	int cnt = 0, i;
 
@@ -621,24 +632,43 @@ static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link,
 					  BPF_MOD_JUMP, NULL,
 					  link->link.prog->bpf_func);
 	}
+	if (kind == BPF_TRAMP_FSESSION) {
+		prog_list = &tr->progs_hlist[BPF_TRAMP_FENTRY];
+		cnt++;
+	} else {
+		prog_list = &tr->progs_hlist[kind];
+	}
 	if (cnt >= BPF_MAX_TRAMP_LINKS)
 		return -E2BIG;
 	if (!hlist_unhashed(&link->tramp_hlist))
 		/* prog already linked */
 		return -EBUSY;
-	hlist_for_each_entry(link_exiting, &tr->progs_hlist[kind], tramp_hlist) {
+	hlist_for_each_entry(link_exiting, prog_list, tramp_hlist) {
 		if (link_exiting->link.prog != link->link.prog)
 			continue;
 		/* prog already linked */
 		return -EBUSY;
 	}
 
-	hlist_add_head(&link->tramp_hlist, &tr->progs_hlist[kind]);
-	tr->progs_cnt[kind]++;
+	hlist_add_head(&link->tramp_hlist, prog_list);
+	if (kind == BPF_TRAMP_FSESSION) {
+		tr->progs_cnt[BPF_TRAMP_FENTRY]++;
+		fslink = container_of(link, struct bpf_fsession_link, link.link);
+		hlist_add_head(&fslink->fexit.tramp_hlist, &tr->progs_hlist[BPF_TRAMP_FEXIT]);
+		tr->progs_cnt[BPF_TRAMP_FEXIT]++;
+	} else {
+		tr->progs_cnt[kind]++;
+	}
 	err = bpf_trampoline_update(tr, true /* lock_direct_mutex */);
 	if (err) {
 		hlist_del_init(&link->tramp_hlist);
-		tr->progs_cnt[kind]--;
+		if (kind == BPF_TRAMP_FSESSION) {
+			tr->progs_cnt[BPF_TRAMP_FENTRY]--;
+			hlist_del_init(&fslink->fexit.tramp_hlist);
+			tr->progs_cnt[BPF_TRAMP_FEXIT]--;
+		} else {
+			tr->progs_cnt[kind]--;
+		}
 	}
 	return err;
 }
@@ -672,6 +702,13 @@ static int __bpf_trampoline_unlink_prog(struct bpf_tramp_link *link,
 		guard(mutex)(&tgt_prog->aux->ext_mutex);
 		tgt_prog->aux->is_extended = false;
 		return err;
+	} else if (kind == BPF_TRAMP_FSESSION) {
+		struct bpf_fsession_link *fslink =
+			container_of(link, struct bpf_fsession_link, link.link);
+
+		hlist_del_init(&fslink->fexit.tramp_hlist);
+		tr->progs_cnt[BPF_TRAMP_FEXIT]--;
+		kind = BPF_TRAMP_FENTRY;
 	}
 	hlist_del_init(&link->tramp_hlist);
 	tr->progs_cnt[kind]--;