[PATCH v3 bpf-next 08/10] 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_link_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       |  32 +++++++++++
 kernel/bpf/syscall.c           | 124 +++++++++++++++++++++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h |  32 +++++++++++
 3 files changed, 188 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 23691ea..8d4556e 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1056,6 +1056,16 @@ enum bpf_link_type {
 	MAX_BPF_LINK_TYPE,
 };
 
+enum bpf_perf_link_type {
+	BPF_PERF_LINK_UNSPEC = 0,
+	BPF_PERF_LINK_UPROBE = 1,
+	BPF_PERF_LINK_KPROBE = 2,
+	BPF_PERF_LINK_TRACEPOINT = 3,
+	BPF_PERF_LINK_PERF_EVENT = 4,
+
+	MAX_BPF_LINK_PERF_EVENT_TYPE,
+};
+
 /* cgroup-bpf attach flags used in BPF_PROG_ATTACH command
  *
  * NONE(default): No further bpf programs allowed in the subtree.
@@ -6443,7 +6453,29 @@ struct bpf_link_info {
 			__u32 count;
 			__u32 flags;
 		} kprobe_multi;
+		struct {
+			__u64 config;
+			__u32 type;
+		} perf_event; /* BPF_LINK_PERF_EVENT_PERF_EVENT */
+		struct {
+			__aligned_u64 file_name; /* in/out: buff ptr */
+			__u32 name_len;
+			__u32 offset;            /* offset from name */
+			__u32 flags;
+		} uprobe; /* BPF_LINK_PERF_EVENT_UPROBE */
+		struct {
+			__aligned_u64 func_name; /* in/out: buff ptr */
+			__u32 name_len;
+			__u32 offset;            /* offset from name */
+			__u64 addr;
+			__u32 flags;
+		} kprobe; /* BPF_LINK_PERF_EVENT_KPROBE */
+		struct {
+			__aligned_u64 tp_name;   /* in/out: buff ptr */
+			__u32 name_len;
+		} tracepoint; /* BPF_LINK_PERF_EVENT_TRACEPOINT */
 	};
+	__u32 perf_link_type; /* enum bpf_perf_link_type */
 } __attribute__((aligned(8)));
 
 /* User bpf_sock_addr struct to access socket fields and sockaddr struct passed
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 80c9ec0..fe354d5 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3303,9 +3303,133 @@ static void bpf_perf_link_dealloc(struct bpf_link *link)
 	kfree(perf_link);
 }
 
+static int bpf_perf_link_fill_name(const struct perf_event *event,
+				   char __user *uname, u32 ulen,
+				   u64 *probe_offset, u64 *probe_addr,
+				   u32 *fd_type)
+{
+	const char *buf;
+	u32 prog_id;
+	size_t len;
+	int err;
+
+	if (!ulen ^ !uname)
+		return -EINVAL;
+	if (!uname)
+		return 0;
+
+	err = bpf_get_perf_event_info(event, &prog_id, fd_type, &buf,
+				      probe_offset, probe_addr);
+	if (err)
+		return err;
+
+	len = strlen(buf);
+	if (buf) {
+		err = bpf_copy_to_user(uname, buf, ulen, len);
+		if (err)
+			return err;
+	} else {
+		char zero = '\0';
+
+		if (put_user(zero, uname))
+			return -EFAULT;
+	}
+	return 0;
+}
+
+static int bpf_perf_link_fill_probe(const struct perf_event *event,
+				    struct bpf_link_info *info)
+{
+	char __user *uname;
+	u64 addr, offset;
+	u32 ulen, type;
+	int err;
+
+#ifdef CONFIG_KPROBE_EVENTS
+	if (event->tp_event->flags & TRACE_EVENT_FL_KPROBE) {
+		uname = u64_to_user_ptr(info->kprobe.func_name);
+		ulen = info->kprobe.name_len;
+		info->perf_link_type = BPF_PERF_LINK_KPROBE;
+		err = bpf_perf_link_fill_name(event, uname, ulen, &offset,
+					      &addr, &type);
+		if (err)
+			return err;
+
+		info->kprobe.offset = offset;
+		if (type == BPF_FD_TYPE_KRETPROBE)
+			info->kprobe.flags = 1;
+		if (!kallsyms_show_value(current_cred()))
+			return 0;
+		info->kprobe.addr = addr;
+		return 0;
+	}
+#endif
+
+#ifdef CONFIG_UPROBE_EVENTS
+	if (event->tp_event->flags & TRACE_EVENT_FL_UPROBE) {
+		uname = u64_to_user_ptr(info->uprobe.file_name);
+		ulen = info->uprobe.name_len;
+		info->perf_link_type = BPF_PERF_LINK_UPROBE;
+		err = bpf_perf_link_fill_name(event, uname, ulen, &offset,
+					      &addr, &type);
+		if (err)
+			return err;
+
+		info->uprobe.offset = offset;
+		if (type == BPF_FD_TYPE_URETPROBE)
+			info->uprobe.flags = 1;
+		return 0;
+	}
+#endif
+
+	return -EOPNOTSUPP;
+}
+
+static int bpf_perf_link_fill_tracepoint(const struct perf_event *event,
+					 struct bpf_link_info *info)
+{
+	char __user *uname = u64_to_user_ptr(info->tracepoint.tp_name);
+	u32 ulen = info->tracepoint.name_len;
+	u64 addr, off;
+	u32 type;
+
+	info->perf_link_type = BPF_PERF_LINK_TRACEPOINT;
+	return bpf_perf_link_fill_name(event, uname, ulen, &off, &addr, &type);
+}
+
+static int bpf_perf_link_fill_perf_event(const struct perf_event *event,
+				    struct bpf_link_info *info)
+{
+	info->perf_event.type = event->attr.type;
+	info->perf_event.config = event->attr.config;
+	info->perf_link_type = BPF_PERF_LINK_PERF_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;
+	if (event->prog->type == BPF_PROG_TYPE_PERF_EVENT)
+		return bpf_perf_link_fill_perf_event(event, info);
+	if (event->prog->type == BPF_PROG_TYPE_TRACEPOINT)
+		return bpf_perf_link_fill_tracepoint(event, info);
+	return bpf_perf_link_fill_probe(event, info);
+}
+
 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..8d4556e 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1056,6 +1056,16 @@ enum bpf_link_type {
 	MAX_BPF_LINK_TYPE,
 };
 
+enum bpf_perf_link_type {
+	BPF_PERF_LINK_UNSPEC = 0,
+	BPF_PERF_LINK_UPROBE = 1,
+	BPF_PERF_LINK_KPROBE = 2,
+	BPF_PERF_LINK_TRACEPOINT = 3,
+	BPF_PERF_LINK_PERF_EVENT = 4,
+
+	MAX_BPF_LINK_PERF_EVENT_TYPE,
+};
+
 /* cgroup-bpf attach flags used in BPF_PROG_ATTACH command
  *
  * NONE(default): No further bpf programs allowed in the subtree.
@@ -6443,7 +6453,29 @@ struct bpf_link_info {
 			__u32 count;
 			__u32 flags;
 		} kprobe_multi;
+		struct {
+			__u64 config;
+			__u32 type;
+		} perf_event; /* BPF_LINK_PERF_EVENT_PERF_EVENT */
+		struct {
+			__aligned_u64 file_name; /* in/out: buff ptr */
+			__u32 name_len;
+			__u32 offset;            /* offset from name */
+			__u32 flags;
+		} uprobe; /* BPF_LINK_PERF_EVENT_UPROBE */
+		struct {
+			__aligned_u64 func_name; /* in/out: buff ptr */
+			__u32 name_len;
+			__u32 offset;            /* offset from name */
+			__u64 addr;
+			__u32 flags;
+		} kprobe; /* BPF_LINK_PERF_EVENT_KPROBE */
+		struct {
+			__aligned_u64 tp_name;   /* in/out: buff ptr */
+			__u32 name_len;
+		} tracepoint; /* BPF_LINK_PERF_EVENT_TRACEPOINT */
 	};
+	__u32 perf_link_type; /* enum bpf_perf_link_type */
 } __attribute__((aligned(8)));
 
 /* User bpf_sock_addr struct to access socket fields and sockaddr struct passed
-- 
1.8.3.1