[PATCH v3 bpf-next 01/10] bpf: Support ->fill_link_info for kprobe_multi

[Yafang Shao <laoar.shao@xxxxxxxxx>]

With the addition of support for fill_link_info to the kprobe_multi link,
users will gain the ability to inspect it conveniently using the
`bpftool link show`. This enhancement provides valuable information to the
user, including the count of probed functions and their respective
addresses. It's important to note that if the kptr_restrict setting is not
permitted, the probed address will not be exposed, ensuring security.

Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
---
 include/uapi/linux/bpf.h       |  5 +++++
 kernel/trace/bpf_trace.c       | 28 ++++++++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h |  5 +++++
 3 files changed, 38 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index a7b5e91..23691ea 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -6438,6 +6438,11 @@ struct bpf_link_info {
 			__s32 priority;
 			__u32 flags;
 		} netfilter;
+		struct {
+			__aligned_u64 addrs; /* in/out: addresses buffer ptr */
+			__u32 count;
+			__u32 flags;
+		} kprobe_multi;
 	};
 } __attribute__((aligned(8)));
 
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 2bc41e6..742047c 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2548,9 +2548,36 @@ static void bpf_kprobe_multi_link_dealloc(struct bpf_link *link)
 	kfree(kmulti_link);
 }
 
+static int bpf_kprobe_multi_link_fill_link_info(const struct bpf_link *link,
+						struct bpf_link_info *info)
+{
+	u64 __user *uaddrs = u64_to_user_ptr(info->kprobe_multi.addrs);
+	struct bpf_kprobe_multi_link *kmulti_link;
+	u32 ucount = info->kprobe_multi.count;
+
+	if (!uaddrs ^ !ucount)
+		return -EINVAL;
+
+	kmulti_link = container_of(link, struct bpf_kprobe_multi_link, link);
+	if (!uaddrs) {
+		info->kprobe_multi.count = kmulti_link->cnt;
+		return 0;
+	}
+
+	if (ucount < kmulti_link->cnt)
+		return -EINVAL;
+	info->kprobe_multi.flags = kmulti_link->fp.flags;
+	if (!kallsyms_show_value(current_cred()))
+		return 0;
+	if (copy_to_user(uaddrs, kmulti_link->addrs, ucount * sizeof(u64)))
+		return -EFAULT;
+	return 0;
+}
+
 static const struct bpf_link_ops bpf_kprobe_multi_link_lops = {
 	.release = bpf_kprobe_multi_link_release,
 	.dealloc = bpf_kprobe_multi_link_dealloc,
+	.fill_link_info = bpf_kprobe_multi_link_fill_link_info,
 };
 
 static void bpf_kprobe_multi_cookie_swap(void *a, void *b, int size, const void *priv)
@@ -2890,6 +2917,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
 		return err;
 	}
 
+	link->fp.flags = flags;
 	return bpf_link_settle(&link_primer);
 
 error:
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index a7b5e91..23691ea 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -6438,6 +6438,11 @@ struct bpf_link_info {
 			__s32 priority;
 			__u32 flags;
 		} netfilter;
+		struct {
+			__aligned_u64 addrs; /* in/out: addresses buffer ptr */
+			__u32 count;
+			__u32 flags;
+		} kprobe_multi;
 	};
 } __attribute__((aligned(8)));
 
-- 
1.8.3.1