bpf: Store cookies in kprobe_multi bpf_link_info data

Storing cookies in kprobe_multi bpf_link_info data. The cookies
field is optional and if provided it needs to be an array of
__u64 with kprobe_multi.count length.
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20240119110505.400573-3-jolsa@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

include/uapi/linux/bpf.h

@@ -6563,6 +6563,7 @@ struct bpf_link_info {
 			__u32 count; /* in/out: kprobe_multi function count */
 			__u32 flags;
 			__u64 missed;
+			__aligned_u64 cookies;
 		} kprobe_multi;
 		struct {
 			__aligned_u64 path;

kernel/trace/bpf_trace.c

@@ -2679,6 +2679,7 @@ static void bpf_kprobe_multi_link_dealloc(struct bpf_link *link)
 static int bpf_kprobe_multi_link_fill_link_info(const struct bpf_link *link,
 						struct bpf_link_info *info)
 {
+	u64 __user *ucookies = u64_to_user_ptr(info->kprobe_multi.cookies);
 	u64 __user *uaddrs = u64_to_user_ptr(info->kprobe_multi.addrs);
 	struct bpf_kprobe_multi_link *kmulti_link;
 	u32 ucount = info->kprobe_multi.count;
@@ -2686,6 +2687,8 @@ static int bpf_kprobe_multi_link_fill_link_info(const struct bpf_link *link,
 
 	if (!uaddrs ^ !ucount)
 		return -EINVAL;
+	if (ucookies && !ucount)
+		return -EINVAL;
 
 	kmulti_link = container_of(link, struct bpf_kprobe_multi_link, link);
 	info->kprobe_multi.count = kmulti_link->cnt;
@@ -2699,6 +2702,18 @@ static int bpf_kprobe_multi_link_fill_link_info(const struct bpf_link *link,
 	else
 		ucount = kmulti_link->cnt;
 
+	if (ucookies) {
+		if (kmulti_link->cookies) {
+			if (copy_to_user(ucookies, kmulti_link->cookies, ucount * sizeof(u64)))
+				return -EFAULT;
+		} else {
+			for (i = 0; i < ucount; i++) {
+				if (put_user(0, ucookies + i))
+					return -EFAULT;
+			}
+		}
+	}
+
 	if (kallsyms_show_value(current_cred())) {
 		if (copy_to_user(uaddrs, kmulti_link->addrs, ucount * sizeof(u64)))
 			return -EFAULT;

tools/include/uapi/linux/bpf.h

@@ -6563,6 +6563,7 @@ struct bpf_link_info {
 			__u32 count; /* in/out: kprobe_multi function count */
 			__u32 flags;
 			__u64 missed;
+			__aligned_u64 cookies;
 		} kprobe_multi;
 		struct {
 			__aligned_u64 path;