bpf: Add support for kprobe session attach

Adding support to attach bpf program for entry and return probe
of the same function. This is common use case which at the moment
requires to create two kprobe multi links.

Adding new BPF_TRACE_KPROBE_SESSION attach type that instructs
kernel to attach single link program to both entry and exit probe.

It's possible to control execution of the bpf program on return
probe simply by returning zero or non zero from the entry bpf
program execution to execute or not the bpf program on return
probe respectively.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240430112830.1184228-2-jolsa@kernel.org

include/uapi/linux/bpf.h

@@ -1115,6 +1115,7 @@ enum bpf_attach_type {
 	BPF_CGROUP_UNIX_GETSOCKNAME,
 	BPF_NETKIT_PRIMARY,
 	BPF_NETKIT_PEER,
+	BPF_TRACE_KPROBE_SESSION,
 	__MAX_BPF_ATTACH_TYPE
 };
 

kernel/bpf/syscall.c

@@ -4016,11 +4016,15 @@ static int bpf_prog_attach_check_attach_type(const struct bpf_prog *prog,
 		if (prog->expected_attach_type == BPF_TRACE_KPROBE_MULTI &&
 		    attach_type != BPF_TRACE_KPROBE_MULTI)
 			return -EINVAL;
+		if (prog->expected_attach_type == BPF_TRACE_KPROBE_SESSION &&
+		    attach_type != BPF_TRACE_KPROBE_SESSION)
+			return -EINVAL;
 		if (prog->expected_attach_type == BPF_TRACE_UPROBE_MULTI &&
 		    attach_type != BPF_TRACE_UPROBE_MULTI)
 			return -EINVAL;
 		if (attach_type != BPF_PERF_EVENT &&
 		    attach_type != BPF_TRACE_KPROBE_MULTI &&
+		    attach_type != BPF_TRACE_KPROBE_SESSION &&
 		    attach_type != BPF_TRACE_UPROBE_MULTI)
 			return -EINVAL;
 		return 0;
@@ -5281,7 +5285,8 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr)
 	case BPF_PROG_TYPE_KPROBE:
 		if (attr->link_create.attach_type == BPF_PERF_EVENT)
 			ret = bpf_perf_link_attach(attr, prog);
-		else if (attr->link_create.attach_type == BPF_TRACE_KPROBE_MULTI)
+		else if (attr->link_create.attach_type == BPF_TRACE_KPROBE_MULTI ||
+			 attr->link_create.attach_type == BPF_TRACE_KPROBE_SESSION)
 			ret = bpf_kprobe_multi_link_attach(attr, prog);
 		else if (attr->link_create.attach_type == BPF_TRACE_UPROBE_MULTI)
 			ret = bpf_uprobe_multi_link_attach(attr, prog);

kernel/trace/bpf_trace.c

@@ -1631,6 +1631,17 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 	}
 }
 
+static bool is_kprobe_multi(const struct bpf_prog *prog)
+{
+	return prog->expected_attach_type == BPF_TRACE_KPROBE_MULTI ||
+	       prog->expected_attach_type == BPF_TRACE_KPROBE_SESSION;
+}
+
+static inline bool is_kprobe_session(const struct bpf_prog *prog)
+{
+	return prog->expected_attach_type == BPF_TRACE_KPROBE_SESSION;
+}
+
 static const struct bpf_func_proto *
 kprobe_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
@@ -1646,13 +1657,13 @@ kprobe_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_override_return_proto;
 #endif
 	case BPF_FUNC_get_func_ip:
-		if (prog->expected_attach_type == BPF_TRACE_KPROBE_MULTI)
+		if (is_kprobe_multi(prog))
 			return &bpf_get_func_ip_proto_kprobe_multi;
 		if (prog->expected_attach_type == BPF_TRACE_UPROBE_MULTI)
 			return &bpf_get_func_ip_proto_uprobe_multi;
 		return &bpf_get_func_ip_proto_kprobe;
 	case BPF_FUNC_get_attach_cookie:
-		if (prog->expected_attach_type == BPF_TRACE_KPROBE_MULTI)
+		if (is_kprobe_multi(prog))
 			return &bpf_get_attach_cookie_proto_kmulti;
 		if (prog->expected_attach_type == BPF_TRACE_UPROBE_MULTI)
 			return &bpf_get_attach_cookie_proto_umulti;
@@ -2834,10 +2845,11 @@ kprobe_multi_link_handler(struct fprobe *fp, unsigned long fentry_ip,
 			  void *data)
 {
 	struct bpf_kprobe_multi_link *link;
+	int err;
 
 	link = container_of(fp, struct bpf_kprobe_multi_link, fp);
-	kprobe_multi_link_prog_run(link, get_entry_ip(fentry_ip), regs);
-	return 0;
+	err = kprobe_multi_link_prog_run(link, get_entry_ip(fentry_ip), regs);
+	return is_kprobe_session(link->link.prog) ? err : 0;
 }
 
 static void
@@ -2981,7 +2993,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 	if (sizeof(u64) != sizeof(void *))
 		return -EOPNOTSUPP;
 
-	if (prog->expected_attach_type != BPF_TRACE_KPROBE_MULTI)
+	if (!is_kprobe_multi(prog))
 		return -EINVAL;
 
 	flags = attr->link_create.kprobe_multi.flags;
@@ -3062,10 +3074,10 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 	if (err)
 		goto error;
 
-	if (flags & BPF_F_KPROBE_MULTI_RETURN)
-		link->fp.exit_handler = kprobe_multi_link_exit_handler;
-	else
+	if (!(flags & BPF_F_KPROBE_MULTI_RETURN))
 		link->fp.entry_handler = kprobe_multi_link_handler;
+	if ((flags & BPF_F_KPROBE_MULTI_RETURN) || is_kprobe_session(prog))
+		link->fp.exit_handler = kprobe_multi_link_exit_handler;
 
 	link->addrs = addrs;
 	link->cookies = cookies;

tools/include/uapi/linux/bpf.h

@@ -1115,6 +1115,7 @@ enum bpf_attach_type {
 	BPF_CGROUP_UNIX_GETSOCKNAME,
 	BPF_NETKIT_PRIMARY,
 	BPF_NETKIT_PEER,
+	BPF_TRACE_KPROBE_SESSION,
 	__MAX_BPF_ATTACH_TYPE
 };