[PATCH v5 bpf-next 09/11] bpf: Support ->fill_link_info for perf_event

[Yafang Shao <laoar.shao@gmail.com>]

By introducing support for ->fill_link_info to the perf_event link, users
gain the ability to inspect it using `bpftool link show`. While the current
approach involves accessing this information via `bpftool perf show`,
consolidating link information for all link types in one place offers
greater convenience. Additionally, this patch extends support to the
generic perf event, which is not currently accommodated by
`bpftool perf show`. While only the perf type and config are exposed to
userspace, other attributes such as sample_period and sample_freq are
ignored. It's important to note that if kptr_restrict is not permitted, the
probed address will not be exposed, maintaining security measures.

A new enum bpf_perf_event_type is introduced to help the user understand
which struct is relevant.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 include/uapi/linux/bpf.h       |  35 +++++++++++++
 kernel/bpf/syscall.c           | 115 +++++++++++++++++++++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h |  35 +++++++++++++
 3 files changed, 185 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 23691ea..1c579d5 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1056,6 +1056,14 @@ enum bpf_link_type {
 	MAX_BPF_LINK_TYPE,
 };
 
+enum bpf_perf_event_type {
+	BPF_PERF_EVENT_UNSPEC = 0,
+	BPF_PERF_EVENT_UPROBE = 1,
+	BPF_PERF_EVENT_KPROBE = 2,
+	BPF_PERF_EVENT_TRACEPOINT = 3,
+	BPF_PERF_EVENT_EVENT = 4,
+};
+
 /* cgroup-bpf attach flags used in BPF_PROG_ATTACH command
  *
  * NONE(default): No further bpf programs allowed in the subtree.
@@ -6443,6 +6451,33 @@ struct bpf_link_info {
 			__u32 count;
 			__u32 flags;
 		} kprobe_multi;
+		struct {
+			__u32 type; /* enum bpf_perf_event_type */
+			__u32 :32;
+			union {
+				struct {
+					__aligned_u64 file_name; /* in/out */
+					__u32 name_len;
+					__u32 offset;/* offset from file_name */
+					__u32 flags;
+				} uprobe; /* BPF_PERF_EVENT_UPROBE */
+				struct {
+					__aligned_u64 func_name; /* in/out */
+					__u32 name_len;
+					__u32 offset;/* offset from func_name */
+					__u64 addr;
+					__u32 flags;
+				} kprobe; /* BPF_PERF_EVENT_KPROBE */
+				struct {
+					__aligned_u64 tp_name;   /* in/out */
+					__u32 name_len;
+				} tracepoint; /* BPF_PERF_EVENT_TRACEPOINT */
+				struct {
+					__u64 config;
+					__u32 type;
+				} event; /* BPF_PERF_EVENT_EVENT */
+			};
+		} perf_event;
 	};
 } __attribute__((aligned(8)));
 
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index c863d39..02dad3c 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3394,9 +3394,124 @@ static int bpf_perf_link_fill_common(const struct perf_event *event,
 	return 0;
 }
 
+#ifdef CONFIG_KPROBE_EVENTS
+static int bpf_perf_link_fill_kprobe(const struct perf_event *event,
+				     struct bpf_link_info *info)
+{
+	char __user *uname;
+	u64 addr, offset;
+	u32 ulen, type;
+	int err;
+
+	uname = u64_to_user_ptr(info->perf_event.kprobe.func_name);
+	ulen = info->perf_event.kprobe.name_len;
+	info->perf_event.type = BPF_PERF_EVENT_KPROBE;
+	err = bpf_perf_link_fill_common(event, uname, ulen, &offset, &addr,
+					&type);
+	if (err)
+		return err;
+
+	info->perf_event.kprobe.offset = offset;
+	if (type == BPF_FD_TYPE_KRETPROBE)
+		info->perf_event.kprobe.flags = 1;
+	if (!kallsyms_show_value(current_cred()))
+		return 0;
+	info->perf_event.kprobe.addr = addr;
+	return 0;
+}
+#endif
+
+#ifdef CONFIG_UPROBE_EVENTS
+static int bpf_perf_link_fill_uprobe(const struct perf_event *event,
+				     struct bpf_link_info *info)
+{
+	char __user *uname;
+	u64 addr, offset;
+	u32 ulen, type;
+	int err;
+
+	uname = u64_to_user_ptr(info->perf_event.uprobe.file_name);
+	ulen = info->perf_event.uprobe.name_len;
+	info->perf_event.type = BPF_PERF_EVENT_UPROBE;
+	err = bpf_perf_link_fill_common(event, uname, ulen, &offset, &addr,
+					&type);
+	if (err)
+		return err;
+
+	info->perf_event.uprobe.offset = offset;
+	if (type == BPF_FD_TYPE_URETPROBE)
+		info->perf_event.uprobe.flags = 1;
+	return 0;
+}
+#endif
+
+static int bpf_perf_link_fill_probe(const struct perf_event *event,
+				    struct bpf_link_info *info)
+{
+#ifdef CONFIG_KPROBE_EVENTS
+	if (event->tp_event->flags & TRACE_EVENT_FL_KPROBE)
+		return bpf_perf_link_fill_kprobe(event, info);
+#endif
+#ifdef CONFIG_UPROBE_EVENTS
+	if (event->tp_event->flags & TRACE_EVENT_FL_UPROBE)
+		return bpf_perf_link_fill_uprobe(event, info);
+#endif
+	return -EOPNOTSUPP;
+}
+
+static int bpf_perf_link_fill_tracepoint(const struct perf_event *event,
+					 struct bpf_link_info *info)
+{
+	char __user *uname;
+	u64 addr, offset;
+	u32 ulen, type;
+
+	uname = u64_to_user_ptr(info->perf_event.tracepoint.tp_name);
+	ulen = info->perf_event.tracepoint.name_len;
+	info->perf_event.type = BPF_PERF_EVENT_TRACEPOINT;
+	return bpf_perf_link_fill_common(event, uname, ulen, &offset, &addr,
+					 &type);
+}
+
+static int bpf_perf_link_fill_perf_event(const struct perf_event *event,
+					 struct bpf_link_info *info)
+{
+	info->perf_event.event.type = event->attr.type;
+	info->perf_event.event.config = event->attr.config;
+	info->perf_event.type = BPF_PERF_EVENT_EVENT;
+	return 0;
+}
+
+static int bpf_perf_link_fill_link_info(const struct bpf_link *link,
+					struct bpf_link_info *info)
+{
+	struct bpf_perf_link *perf_link;
+	const struct perf_event *event;
+
+	perf_link = container_of(link, struct bpf_perf_link, link);
+	event = perf_get_event(perf_link->perf_file);
+	if (IS_ERR(event))
+		return PTR_ERR(event);
+
+	if (!event->prog)
+		return -EINVAL;
+
+	switch (event->prog->type) {
+	case BPF_PROG_TYPE_PERF_EVENT:
+		return bpf_perf_link_fill_perf_event(event, info);
+	case BPF_PROG_TYPE_TRACEPOINT:
+		return bpf_perf_link_fill_tracepoint(event, info);
+	case BPF_PROG_TYPE_KPROBE:
+		return bpf_perf_link_fill_probe(event, info);
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
 static const struct bpf_link_ops bpf_perf_link_lops = {
 	.release = bpf_perf_link_release,
 	.dealloc = bpf_perf_link_dealloc,
+	.fill_link_info = bpf_perf_link_fill_link_info,
 };
 
 static int bpf_perf_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 23691ea..1c579d5 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1056,6 +1056,14 @@ enum bpf_link_type {
 	MAX_BPF_LINK_TYPE,
 };
 
+enum bpf_perf_event_type {
+	BPF_PERF_EVENT_UNSPEC = 0,
+	BPF_PERF_EVENT_UPROBE = 1,
+	BPF_PERF_EVENT_KPROBE = 2,
+	BPF_PERF_EVENT_TRACEPOINT = 3,
+	BPF_PERF_EVENT_EVENT = 4,
+};
+
 /* cgroup-bpf attach flags used in BPF_PROG_ATTACH command
  *
  * NONE(default): No further bpf programs allowed in the subtree.
@@ -6443,6 +6451,33 @@ struct bpf_link_info {
 			__u32 count;
 			__u32 flags;
 		} kprobe_multi;
+		struct {
+			__u32 type; /* enum bpf_perf_event_type */
+			__u32 :32;
+			union {
+				struct {
+					__aligned_u64 file_name; /* in/out */
+					__u32 name_len;
+					__u32 offset;/* offset from file_name */
+					__u32 flags;
+				} uprobe; /* BPF_PERF_EVENT_UPROBE */
+				struct {
+					__aligned_u64 func_name; /* in/out */
+					__u32 name_len;
+					__u32 offset;/* offset from func_name */
+					__u64 addr;
+					__u32 flags;
+				} kprobe; /* BPF_PERF_EVENT_KPROBE */
+				struct {
+					__aligned_u64 tp_name;   /* in/out */
+					__u32 name_len;
+				} tracepoint; /* BPF_PERF_EVENT_TRACEPOINT */
+				struct {
+					__u64 config;
+					__u32 type;
+				} event; /* BPF_PERF_EVENT_EVENT */
+			};
+		} perf_event;
 	};
 } __attribute__((aligned(8)));
 
-- 
1.8.3.1