[PATCH bpf-next v2 2/6] bpf: Add syscall common attrs support for xdp link_create

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

With the syscall common attrs support for link_create, add syscall common
attrs support for xdp link_create in order to report the invalid target
ifindex error and the underlying driver's error.

Define a stub bpf_log() when CONFIG_BPF_SYSCALL is not set. Afterwards,
bpf_log() can be called without CONFIG_BPF_SYSCALL guard in
net/core/dev.c.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 include/linux/bpf_verifier.h | 5 +++++
 include/linux/netdevice.h    | 3 ++-
 kernel/bpf/syscall.c         | 2 +-
 net/core/dev.c               | 7 ++++++-
 4 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index de9845526ce0..0b8f764157fc 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -1259,8 +1259,13 @@ __printf(2, 0) void bpf_verifier_vlog(struct bpf_verifier_log *log,
 				      const char *fmt, va_list args);
 __printf(2, 3) void bpf_verifier_log_write(struct bpf_verifier_env *env,
 					   const char *fmt, ...);
+#ifdef CONFIG_BPF_SYSCALL
 __printf(2, 3) void bpf_log(struct bpf_verifier_log *log,
 			    const char *fmt, ...);
+#else
+__printf(2, 3) static inline void bpf_log(struct bpf_verifier_log *log,
+					  const char *fmt, ...) {}
+#endif
 int bpf_vlog_init(struct bpf_verifier_log *log, u32 log_level,
 		  char __user *log_buf, u32 log_size);
 void bpf_vlog_reset(struct bpf_verifier_log *log, u64 new_pos);
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 3cff2174dc03..4548b0fd824d 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -4417,7 +4417,8 @@ struct sk_buff *validate_xmit_skb_list(struct sk_buff *skb, struct net_device *d
 struct sk_buff *dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev,
 				    struct netdev_queue *txq, int *ret);
 
-int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);
+int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog,
+			struct bpf_verifier_log *log);
 u8 dev_xdp_prog_count(struct net_device *dev);
 int netif_xdp_propagate(struct net_device *dev, struct netdev_bpf *bpf);
 int dev_xdp_propagate(struct net_device *dev, struct netdev_bpf *bpf);
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 201658b75ab7..5652ecf21289 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -5942,7 +5942,7 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr, struct bpf_common_a
 		break;
 #ifdef CONFIG_NET
 	case BPF_PROG_TYPE_XDP:
-		ret = bpf_xdp_link_attach(attr, prog);
+		ret = bpf_xdp_link_attach(attr, prog, log);
 		break;
 	case BPF_PROG_TYPE_SCHED_CLS:
 		if (attr->link_create.attach_type == BPF_TCX_INGRESS ||
diff --git a/net/core/dev.c b/net/core/dev.c
index 18dc88990510..96be63b9331e 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -97,6 +97,7 @@
 #include <linux/kthread.h>
 #include <linux/bpf.h>
 #include <linux/bpf_trace.h>
+#include <linux/bpf_verifier.h>
 #include <net/net_namespace.h>
 #include <net/sock.h>
 #include <net/busy_poll.h>
@@ -10771,7 +10772,8 @@ static const struct bpf_link_ops bpf_xdp_link_lops = {
 	.update_prog = bpf_xdp_link_update,
 };
 
-int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
+int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog,
+			struct bpf_verifier_log *log)
 {
 	struct net *net = current->nsproxy->net_ns;
 	struct bpf_link_primer link_primer;
@@ -10784,6 +10786,7 @@ int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
 	dev = dev_get_by_index(net, attr->link_create.target_ifindex);
 	if (!dev) {
 		rtnl_unlock();
+		bpf_log(log, "Invalid target_ifindex.\n");
 		return -EINVAL;
 	}
 
@@ -10812,6 +10815,8 @@ int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
 	if (err) {
 		link->dev = NULL;
 		bpf_link_cleanup(&link_primer);
+		if (extack._msg)
+			bpf_log(log, "%s\n", extack._msg);
 		trace_bpf_xdp_link_attach_failed(extack._msg);
 		goto out_put_dev;
 	}
-- 
2.55.0