bpf: add initial bpf tracepoints

This work adds a number of tracepoints to paths that are either
considered slow-path or exception-like states, where monitoring or
inspecting them would be desirable.

For bpf(2) syscall, tracepoints have been placed for main commands
when they succeed. In XDP case, tracepoint is for exceptions, that
is, f.e. on abnormal BPF program exit such as unknown or XDP_ABORTED
return code, or when error occurs during XDP_TX action and the packet
could not be forwarded.

Both have been split into separate event headers, and can be further
extended. Worst case, if they unexpectedly should get into our way in
future, they can also removed [1]. Of course, these tracepoints (like
any other) can be analyzed by eBPF itself, etc. Example output:

  # ./perf record -a -e bpf:* sleep 10
  # ./perf script
  sock_example  6197 [005]   283.980322:      bpf:bpf_map_create: map type=ARRAY ufd=4 key=4 val=8 max=256 flags=0
  sock_example  6197 [005]   283.980721:       bpf:bpf_prog_load: prog=a5ea8fa30ea6849c type=SOCKET_FILTER ufd=5
  sock_example  6197 [005]   283.988423:   bpf:bpf_prog_get_type: prog=a5ea8fa30ea6849c type=SOCKET_FILTER
  sock_example  6197 [005]   283.988443: bpf:bpf_map_lookup_elem: map type=ARRAY ufd=4 key=[06 00 00 00] val=[00 00 00 00 00 00 00 00]
  [...]
  sock_example  6197 [005]   288.990868: bpf:bpf_map_lookup_elem: map type=ARRAY ufd=4 key=[01 00 00 00] val=[14 00 00 00 00 00 00 00]
       swapper     0 [005]   289.338243:    bpf:bpf_prog_put_rcu: prog=a5ea8fa30ea6849c type=SOCKET_FILTER

  [1] https://lwn.net/Articles/705270/

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

kernel/bpf/core.c

@@ -1173,3 +1173,12 @@ int __weak skb_copy_bits(const struct sk_buff *skb, int offset, void *to,
 {
 	return -EFAULT;
 }
+
+/* All definitions of tracepoints related to BPF. */
+#define CREATE_TRACE_POINTS
+#include <linux/bpf_trace.h>
+
+EXPORT_TRACEPOINT_SYMBOL_GPL(xdp_exception);
+
+EXPORT_TRACEPOINT_SYMBOL_GPL(bpf_prog_get_type);
+EXPORT_TRACEPOINT_SYMBOL_GPL(bpf_prog_put_rcu);

kernel/bpf/inode.c

@@ -21,6 +21,7 @@
 #include <linux/parser.h>
 #include <linux/filter.h>
 #include <linux/bpf.h>
+#include <linux/bpf_trace.h>
 
 enum bpf_type {
 	BPF_TYPE_UNSPEC	= 0,
@@ -281,6 +282,13 @@ int bpf_obj_pin_user(u32 ufd, const char __user *pathname)
 	ret = bpf_obj_do_pin(pname, raw, type);
 	if (ret != 0)
 		bpf_any_put(raw, type);
+	if ((trace_bpf_obj_pin_prog_enabled() ||
+	     trace_bpf_obj_pin_map_enabled()) && !ret) {
+		if (type == BPF_TYPE_PROG)
+			trace_bpf_obj_pin_prog(raw, ufd, pname);
+		if (type == BPF_TYPE_MAP)
+			trace_bpf_obj_pin_map(raw, ufd, pname);
+	}
 out:
 	putname(pname);
 	return ret;
@@ -342,8 +350,15 @@ int bpf_obj_get_user(const char __user *pathname)
 	else
 		goto out;
 
-	if (ret < 0)
+	if (ret < 0) {
 		bpf_any_put(raw, type);
+	} else if (trace_bpf_obj_get_prog_enabled() ||
+		   trace_bpf_obj_get_map_enabled()) {
+		if (type == BPF_TYPE_PROG)
+			trace_bpf_obj_get_prog(raw, ret, pname);
+		if (type == BPF_TYPE_MAP)
+			trace_bpf_obj_get_map(raw, ret, pname);
+	}
 out:
 	putname(pname);
 	return ret;

kernel/bpf/syscall.c

@@ -10,6 +10,7 @@
  * General Public License for more details.
  */
 #include <linux/bpf.h>
+#include <linux/bpf_trace.h>
 #include <linux/syscalls.h>
 #include <linux/slab.h>
 #include <linux/anon_inodes.h>
@@ -215,6 +216,7 @@ static int map_create(union bpf_attr *attr)
 		/* failed to allocate fd */
 		goto free_map;
 
+	trace_bpf_map_create(map, err);
 	return err;
 
 free_map:
@@ -339,6 +341,7 @@ static int map_lookup_elem(union bpf_attr *attr)
 	if (copy_to_user(uvalue, value, value_size) != 0)
 		goto free_value;
 
+	trace_bpf_map_lookup_elem(map, ufd, key, value);
 	err = 0;
 
 free_value:
@@ -421,6 +424,8 @@ static int map_update_elem(union bpf_attr *attr)
 	__this_cpu_dec(bpf_prog_active);
 	preempt_enable();
 
+	if (!err)
+		trace_bpf_map_update_elem(map, ufd, key, value);
 free_value:
 	kfree(value);
 free_key:
@@ -466,6 +471,8 @@ static int map_delete_elem(union bpf_attr *attr)
 	__this_cpu_dec(bpf_prog_active);
 	preempt_enable();
 
+	if (!err)
+		trace_bpf_map_delete_elem(map, ufd, key);
 free_key:
 	kfree(key);
 err_put:
@@ -518,6 +525,7 @@ static int map_get_next_key(union bpf_attr *attr)
 	if (copy_to_user(unext_key, next_key, map->key_size) != 0)
 		goto free_next_key;
 
+	trace_bpf_map_next_key(map, ufd, key, next_key);
 	err = 0;
 
 free_next_key:
@@ -671,8 +679,10 @@ static void __bpf_prog_put_rcu(struct rcu_head *rcu)
 
 void bpf_prog_put(struct bpf_prog *prog)
 {
-	if (atomic_dec_and_test(&prog->aux->refcnt))
+	if (atomic_dec_and_test(&prog->aux->refcnt)) {
+		trace_bpf_prog_put_rcu(prog);
 		call_rcu(&prog->aux->rcu, __bpf_prog_put_rcu);
+	}
 }
 EXPORT_SYMBOL_GPL(bpf_prog_put);
 
@@ -781,7 +791,11 @@ struct bpf_prog *bpf_prog_get(u32 ufd)
 
 struct bpf_prog *bpf_prog_get_type(u32 ufd, enum bpf_prog_type type)
 {
-	return __bpf_prog_get(ufd, &type);
+	struct bpf_prog *prog = __bpf_prog_get(ufd, &type);
+
+	if (!IS_ERR(prog))
+		trace_bpf_prog_get_type(prog);
+	return prog;
 }
 EXPORT_SYMBOL_GPL(bpf_prog_get_type);
 
@@ -863,6 +877,7 @@ static int bpf_prog_load(union bpf_attr *attr)
 		/* failed to allocate fd */
 		goto free_used_maps;
 
+	trace_bpf_prog_load(prog, err);
 	return err;
 
 free_used_maps: