[PATCH bpf-next 1/9] bpf: Add log support for tracing link_create

[Leon Hwang <leon.hwang@linux.dev>]

Tracing BPF_LINK_CREATE returns an error without explaining why attachment
failed.

Pass the BPF_LINK_CREATE log to the tracing attach path and report invalid
attach parameters. Also pass it to bpf_check_attach_target() so freplace
attachment to a new target can report target-check failures.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 kernel/bpf/syscall.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 9004f2673ccf..6147d386b777 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3674,7 +3674,8 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog,
 				   int tgt_prog_fd,
 				   u32 btf_id,
 				   u64 bpf_cookie,
-				   enum bpf_attach_type attach_type)
+				   enum bpf_attach_type attach_type,
+				   struct bpf_verifier_log *log)
 {
 	struct bpf_link_primer link_primer;
 	struct bpf_prog *tgt_prog = NULL;
@@ -3711,6 +3712,7 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog,
 	}
 
 	if (!!tgt_prog_fd != !!btf_id) {
+		bpf_log(log, "tgt_prog_fd and btf_id must be both set or both unset.\n");
 		err = -EINVAL;
 		goto out_put_prog;
 	}
@@ -3723,12 +3725,14 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog,
 		 * attach_tracing_prog flag is set.
 		 */
 		if (prog->type != BPF_PROG_TYPE_EXT) {
+			bpf_log(log, "tgt_prog_fd is only allowed for freplace prog.\n");
 			err = -EINVAL;
 			goto out_put_prog;
 		}
 
 		tgt_prog = bpf_prog_get(tgt_prog_fd);
 		if (IS_ERR(tgt_prog)) {
+			bpf_log(log, "Invalid tgt_prog_fd.\n");
 			err = PTR_ERR(tgt_prog);
 			tgt_prog = NULL;
 			goto out_put_prog;
@@ -3783,11 +3787,13 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog,
 		 */
 		if (prog->type != BPF_PROG_TYPE_TRACING &&
 		    prog->type != BPF_PROG_TYPE_LSM) {
+			bpf_log(log, "Only allow re-attach for tracing and lsm progs.\n");
 			err = -EINVAL;
 			goto out_unlock;
 		}
 		/* We can allow re-attach only if we have valid attach_btf. */
 		if (!prog->aux->attach_btf) {
+			bpf_log(log, "Invalid attach_btf.\n");
 			err = -EINVAL;
 			goto out_unlock;
 		}
@@ -3803,7 +3809,7 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog,
 		 */
 		struct bpf_attach_target_info tgt_info = {};
 
-		err = bpf_check_attach_target(NULL, prog, tgt_prog, btf_id,
+		err = bpf_check_attach_target(log, prog, tgt_prog, btf_id,
 					      &tgt_info);
 		if (err)
 			goto out_unlock;
@@ -3843,6 +3849,7 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog,
 	 */
 	if (prog->type == BPF_PROG_TYPE_EXT &&
 	    prog->aux->kprobe_write_ctx != tgt_prog->aux->kprobe_write_ctx) {
+		bpf_log(log, "Invalid kprobe_write_ctx.\n");
 		err = -EINVAL;
 		goto out_unlock;
 	}
@@ -4374,7 +4381,7 @@ static int bpf_raw_tp_link_attach(struct bpf_prog *prog,
 			tp_name = prog->aux->attach_func_name;
 			break;
 		}
-		return bpf_tracing_prog_attach(prog, 0, 0, 0, attach_type);
+		return bpf_tracing_prog_attach(prog, 0, 0, 0, attach_type, NULL);
 	case BPF_PROG_TYPE_RAW_TRACEPOINT:
 	case BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE:
 		if (strncpy_from_user(buf, user_tp_name, sizeof(buf) - 1) < 0)
@@ -5907,11 +5914,13 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr, struct bpf_common_a
 					      attr->link_create.target_fd,
 					      attr->link_create.target_btf_id,
 					      attr->link_create.tracing.cookie,
-					      attr->link_create.attach_type);
+					      attr->link_create.attach_type,
+					      log);
 		break;
 	case BPF_PROG_TYPE_LSM:
 	case BPF_PROG_TYPE_TRACING:
 		if (attr->link_create.attach_type != prog->expected_attach_type) {
+			bpf_log(log, "Invalid attach_type.\n");
 			ret = -EINVAL;
 			goto out;
 		}
@@ -5929,7 +5938,8 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr, struct bpf_common_a
 						      attr->link_create.target_fd,
 						      attr->link_create.target_btf_id,
 						      attr->link_create.tracing.cookie,
-						      attr->link_create.attach_type);
+						      attr->link_create.attach_type,
+						      log);
 		break;
 	case BPF_PROG_TYPE_FLOW_DISSECTOR:
 	case BPF_PROG_TYPE_SK_LOOKUP:
-- 
2.55.0