[PATCH v2 bpf-next 08/11] bpf: Support ->fill_link_info for perf_event

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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 set to 2, the
probed address will not be exposed, maintaining security measures.

Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
---
 include/uapi/linux/bpf.h       | 22 ++++++++++
 kernel/bpf/syscall.c           | 98 ++++++++++++++++++++++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h | 22 ++++++++++
 3 files changed, 142 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index d99cc16..c3b821d 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -6443,6 +6443,28 @@ struct bpf_link_info {
 			__u32 count;
 			__u8  retprobe;
 		} kprobe_multi;
+		union {
+			struct {
+				/* The name is:
+				 * a) uprobe: file name
+				 * b) kprobe: kernel function
+				 */
+				__aligned_u64 name; /* in/out: name buffer ptr */
+				__u32 name_len;
+				__u32 offset;	/* offset from the name */
+				__u64 addr;
+				__u8 retprobe;
+			} probe; /* uprobe, kprobe */
+			struct {
+				/* in/out: tracepoint name buffer ptr */
+				__aligned_u64 tp_name;
+				__u32 name_len;
+			} tp; /* tracepoint */
+			struct {
+				__u64 config;
+				__u32 type;
+			} event; /* generic perf event */
+		} perf_event;
 	};
 } __attribute__((aligned(8)));
 
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 80c9ec0..e349bdb 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3303,9 +3303,107 @@ 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_to_user_ptr(info->perf_event.probe.name);
+	u32 ulen = info->perf_event.probe.name_len;
+	u64 addr, off;
+	u32 type;
+	int err;
+
+	err = bpf_perf_link_fill_name(event, uname, ulen, &off, &addr, &type);
+	if (err)
+		return err;
+	info->perf_event.probe.offset = off;
+	if (type == BPF_FD_TYPE_KRETPROBE || type == BPF_FD_TYPE_URETPROBE)
+		info->perf_event.probe.retprobe = 1;
+	else
+		info->perf_event.probe.retprobe = 0;
+
+	if (kptr_restrict == 2)
+		return 0;
+	info->perf_event.probe.addr = addr;
+	return 0;
+}
+
+static int bpf_perf_link_fill_tp(const struct perf_event *event,
+				 struct bpf_link_info *info)
+{
+	char __user *uname = u64_to_user_ptr(info->perf_event.tp.tp_name);
+	u32 ulen = info->perf_event.tp.name_len;
+	u64 addr, off;
+	u32 type;
+
+	return bpf_perf_link_fill_name(event, uname, ulen, &off, &addr, &type);
+}
+
+static int bpf_perf_link_fill_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;
+	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_event(event, info);
+	if (event->prog->type == BPF_PROG_TYPE_TRACEPOINT)
+		return bpf_perf_link_fill_tp(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 d99cc16..c3b821d 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -6443,6 +6443,28 @@ struct bpf_link_info {
 			__u32 count;
 			__u8  retprobe;
 		} kprobe_multi;
+		union {
+			struct {
+				/* The name is:
+				 * a) uprobe: file name
+				 * b) kprobe: kernel function
+				 */
+				__aligned_u64 name; /* in/out: name buffer ptr */
+				__u32 name_len;
+				__u32 offset;	/* offset from the name */
+				__u64 addr;
+				__u8 retprobe;
+			} probe; /* uprobe, kprobe */
+			struct {
+				/* in/out: tracepoint name buffer ptr */
+				__aligned_u64 tp_name;
+				__u32 name_len;
+			} tp; /* tracepoint */
+			struct {
+				__u64 config;
+				__u32 type;
+			} event; /* generic perf event */
+		} perf_event;
 	};
 } __attribute__((aligned(8)));
 
-- 
1.8.3.1





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