bpf: Add struct bpf_trampoline_ops object

In following changes we will need to override ftrace direct attachment
behaviour. In order to do that we are adding struct bpf_trampoline_ops
object that defines callbacks for ftrace direct attachment:

   register_fentry
   unregister_fentry
   modify_fentry

The new struct bpf_trampoline_ops object is passed as an argument to
__bpf_trampoline_link/unlink_prog functions.

At the moment the default trampoline_ops is set to the current ftrace
direct attachment functions, so there's no functional change for the
current code.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20260606123955.345967-6-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 41 insertions, 18 deletions

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index c0b4732627be..5c943832fb9d 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -59,8 +59,18 @@ static void trampoline_unlock(struct bpf_trampoline *tr)
 	mutex_unlock(select_trampoline_lock(tr));
 }
 
+struct bpf_trampoline_ops {
+	int (*register_fentry)(struct bpf_trampoline *tr, void *new_addr, void *data);
+	int (*unregister_fentry)(struct bpf_trampoline *tr, u32 orig_flags, void *old_addr,
+				 void *data);
+	int (*modify_fentry)(struct bpf_trampoline *tr, u32 orig_flags, void *old_addr,
+			     void *new_addr, bool lock_direct_mutex, void *data);
+};
+
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
-static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mutex);
+static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mutex,
+				 const struct bpf_trampoline_ops *ops, void *data);
+static const struct bpf_trampoline_ops trampoline_ops;
 
 #ifdef CONFIG_HAVE_SINGLE_FTRACE_DIRECT_OPS
 static struct bpf_trampoline *direct_ops_ip_lookup(struct ftrace_ops *ops, unsigned long ip)
@@ -145,13 +155,15 @@ static int bpf_tramp_ftrace_ops_func(struct ftrace_ops *ops, unsigned long ip,
 
 		if ((tr->flags & BPF_TRAMP_F_CALL_ORIG) &&
 		    !(tr->flags & BPF_TRAMP_F_ORIG_STACK))
-			ret = bpf_trampoline_update(tr, false /* lock_direct_mutex */);
+			ret = bpf_trampoline_update(tr, false /* lock_direct_mutex */,
+						    &trampoline_ops, NULL);
 		break;
 	case FTRACE_OPS_CMD_DISABLE_SHARE_IPMODIFY_PEER:
 		tr->flags &= ~BPF_TRAMP_F_SHARE_IPMODIFY;
 
 		if (tr->flags & BPF_TRAMP_F_ORIG_STACK)
-			ret = bpf_trampoline_update(tr, false /* lock_direct_mutex */);
+			ret = bpf_trampoline_update(tr, false /* lock_direct_mutex */,
+						    &trampoline_ops, NULL);
 		break;
 	default:
 		ret = -EINVAL;
@@ -415,7 +427,7 @@ static int bpf_trampoline_update_fentry(struct bpf_trampoline *tr, u32 orig_flag
 }
 
 static int unregister_fentry(struct bpf_trampoline *tr, u32 orig_flags,
-			     void *old_addr)
+			     void *old_addr, void *data __maybe_unused)
 {
 	int ret;
 
@@ -429,7 +441,7 @@ static int unregister_fentry(struct bpf_trampoline *tr, u32 orig_flags,
 
 static int modify_fentry(struct bpf_trampoline *tr, u32 orig_flags,
 			 void *old_addr, void *new_addr,
-			 bool lock_direct_mutex)
+			 bool lock_direct_mutex, void *data __maybe_unused)
 {
 	int ret;
 
@@ -443,7 +455,7 @@ static int modify_fentry(struct bpf_trampoline *tr, u32 orig_flags,
 }
 
 /* first time registering */
-static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
+static int register_fentry(struct bpf_trampoline *tr, void *new_addr, void *data __maybe_unused)
 {
 	void *ip = tr->func.addr;
 	unsigned long faddr;
@@ -465,6 +477,12 @@ static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
 	return ret;
 }
 
+static const struct bpf_trampoline_ops trampoline_ops = {
+	.register_fentry   = register_fentry,
+	.unregister_fentry = unregister_fentry,
+	.modify_fentry     = modify_fentry,
+};
+
 static struct bpf_tramp_links *
 bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total, bool *ip_arg)
 {
@@ -632,7 +650,8 @@ out:
 	return ERR_PTR(err);
 }
 
-static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mutex)
+static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mutex,
+				 const struct bpf_trampoline_ops *ops, void *data)
 {
 	struct bpf_tramp_image *im;
 	struct bpf_tramp_links *tlinks;
@@ -645,7 +664,7 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
 		return PTR_ERR(tlinks);
 
 	if (total == 0) {
-		err = unregister_fentry(tr, orig_flags, tr->cur_image->image);
+		err = ops->unregister_fentry(tr, orig_flags, tr->cur_image->image, data);
 		bpf_tramp_image_put(tr->cur_image);
 		tr->cur_image = NULL;
 		goto out;
@@ -715,11 +734,11 @@ again:
 
 	if (tr->cur_image)
 		/* progs already running at this address */
-		err = modify_fentry(tr, orig_flags, tr->cur_image->image,
-				    im->image, lock_direct_mutex);
+		err = ops->modify_fentry(tr, orig_flags, tr->cur_image->image,
+					 im->image, lock_direct_mutex, data);
 	else
 		/* first time registering */
-		err = register_fentry(tr, im->image);
+		err = ops->register_fentry(tr, im->image, data);
 
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 	if (err == -EAGAIN) {
@@ -793,7 +812,9 @@ static int bpf_freplace_check_tgt_prog(struct bpf_prog *tgt_prog)
 
 static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link,
 				      struct bpf_trampoline *tr,
-				      struct bpf_prog *tgt_prog)
+				      struct bpf_prog *tgt_prog,
+				      const struct bpf_trampoline_ops *ops,
+				      void *data)
 {
 	struct bpf_fsession_link *fslink = NULL;
 	enum bpf_tramp_prog_type kind;
@@ -851,7 +872,7 @@ static int __bpf_trampoline_link_prog(struct bpf_tramp_link *link,
 	} else {
 		tr->progs_cnt[kind]++;
 	}
-	err = bpf_trampoline_update(tr, true /* lock_direct_mutex */);
+	err = bpf_trampoline_update(tr, true /* lock_direct_mutex */, ops, data);
 	if (err) {
 		hlist_del_init(&link->tramp_hlist);
 		if (kind == BPF_TRAMP_FSESSION) {
@@ -872,14 +893,16 @@ int bpf_trampoline_link_prog(struct bpf_tramp_link *link,
 	int err;
 
 	trampoline_lock(tr);
-	err = __bpf_trampoline_link_prog(link, tr, tgt_prog);
+	err = __bpf_trampoline_link_prog(link, tr, tgt_prog, &trampoline_ops, NULL);
 	trampoline_unlock(tr);
 	return err;
 }
 
 static int __bpf_trampoline_unlink_prog(struct bpf_tramp_link *link,
 					struct bpf_trampoline *tr,
-					struct bpf_prog *tgt_prog)
+					struct bpf_prog *tgt_prog,
+					const struct bpf_trampoline_ops *ops,
+					void *data)
 {
 	enum bpf_tramp_prog_type kind;
 	int err;
@@ -904,7 +927,7 @@ static int __bpf_trampoline_unlink_prog(struct bpf_tramp_link *link,
 	}
 	hlist_del_init(&link->tramp_hlist);
 	tr->progs_cnt[kind]--;
-	return bpf_trampoline_update(tr, true /* lock_direct_mutex */);
+	return bpf_trampoline_update(tr, true /* lock_direct_mutex */, ops, data);
 }
 
 /* bpf_trampoline_unlink_prog() should never fail. */
@@ -915,7 +938,7 @@ int bpf_trampoline_unlink_prog(struct bpf_tramp_link *link,
 	int err;
 
 	trampoline_lock(tr);
-	err = __bpf_trampoline_unlink_prog(link, tr, tgt_prog);
+	err = __bpf_trampoline_unlink_prog(link, tr, tgt_prog, &trampoline_ops, NULL);
 	trampoline_unlock(tr);
 	return err;
 }
@@ -1044,7 +1067,7 @@ int bpf_trampoline_link_cgroup_shim(struct bpf_prog *prog,
 		goto err;
 	}
 
-	err = __bpf_trampoline_link_prog(&shim_link->link, tr, NULL);
+	err = __bpf_trampoline_link_prog(&shim_link->link, tr, NULL, &trampoline_ops, NULL);
 	if (err)
 		goto err;