bpf: Add cb access in kfree_skb test

Access the skb->cb[] in the kfree_skb test.
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191107180905.4097871-1-kafai@fb.com

tools/testing/selftests/bpf/prog_tests/kfree_skb.c

 // SPDX-License-Identifier: GPL-2.0
 #include <test_progs.h>
 
+struct meta {
+	int ifindex;
+	__u32 cb32_0;
+	__u8 cb8_0;
+};
+
+static union {
+	__u32 cb32[5];
+	__u8 cb8[20];
+} cb = {
+	.cb32[0] = 0x81828384,
+};
+
 static void on_sample(void *ctx, int cpu, void *data, __u32 size)
 {
-	int ifindex = *(int *)data, duration = 0;
-	struct ipv6_packet *pkt_v6 = data + 4;
+	struct meta *meta = (struct meta *)data;
+	struct ipv6_packet *pkt_v6 = data + sizeof(*meta);
+	int duration = 0;
 
-	if (ifindex != 1)
+	if (CHECK(size != 72 + sizeof(*meta), "check_size", "size %u != %zu\n",
+		  size, 72 + sizeof(*meta)))
+		return;
+	if (CHECK(meta->ifindex != 1, "check_meta_ifindex",
+		  "meta->ifindex = %d\n", meta->ifindex))
 		/* spurious kfree_skb not on loopback device */
 		return;
-	if (CHECK(size != 76, "check_size", "size %u != 76\n", size))
+	if (CHECK(meta->cb8_0 != cb.cb8[0], "check_cb8_0", "cb8_0 %x != %x\n",
+		  meta->cb8_0, cb.cb8[0]))
+		return;
+	if (CHECK(meta->cb32_0 != cb.cb32[0], "check_cb32_0",
+		  "cb32_0 %x != %x\n",
+		  meta->cb32_0, cb.cb32[0]))
 		return;
 	if (CHECK(pkt_v6->eth.h_proto != 0xdd86, "check_eth",
 		  "h_proto %x\n", pkt_v6->eth.h_proto))
@@ -26,6 +49,13 @@ static void on_sample(void *ctx, int cpu, void *data, __u32 size)
 
 void test_kfree_skb(void)
 {
+	struct __sk_buff skb = {};
+	struct bpf_prog_test_run_attr tattr = {
+		.data_in = &pkt_v6,
+		.data_size_in = sizeof(pkt_v6),
+		.ctx_in = &skb,
+		.ctx_size_in = sizeof(skb),
+	};
 	struct bpf_prog_load_attr attr = {
 		.file = "./kfree_skb.o",
 	};
@@ -36,11 +66,12 @@ void test_kfree_skb(void)
 	struct bpf_link *link = NULL;
 	struct bpf_map *perf_buf_map;
 	struct bpf_program *prog;
-	__u32 duration, retval;
-	int err, pkt_fd, kfree_skb_fd;
+	int err, kfree_skb_fd;
 	bool passed = false;
+	__u32 duration = 0;
 
-	err = bpf_prog_load("./test_pkt_access.o", BPF_PROG_TYPE_SCHED_CLS, &obj, &pkt_fd);
+	err = bpf_prog_load("./test_pkt_access.o", BPF_PROG_TYPE_SCHED_CLS,
+			    &obj, &tattr.prog_fd);
 	if (CHECK(err, "prog_load sched cls", "err %d errno %d\n", err, errno))
 		return;
 
@@ -66,11 +97,12 @@ void test_kfree_skb(void)
 	if (CHECK(IS_ERR(pb), "perf_buf__new", "err %ld\n", PTR_ERR(pb)))
 		goto close_prog;
 
-	err = bpf_prog_test_run(pkt_fd, 1, &pkt_v6, sizeof(pkt_v6),
-				NULL, NULL, &retval, &duration);
-	CHECK(err || retval, "ipv6",
+	memcpy(skb.cb, &cb, sizeof(cb));
+	err = bpf_prog_test_run_xattr(&tattr);
+	duration = tattr.duration;
+	CHECK(err || tattr.retval, "ipv6",
 	      "err %d errno %d retval %d duration %d\n",
-	      err, errno, retval, duration);
+	      err, errno, tattr.retval, duration);
 
 	/* read perf buffer */
 	err = perf_buffer__poll(pb, 100);

tools/testing/selftests/bpf/progs/kfree_skb.c

@@ -43,6 +43,7 @@ struct sk_buff {
 	refcount_t users;
 	unsigned char *data;
 	char __pkt_type_offset[0];
+	char cb[48];
 };
 
 /* copy arguments from
@@ -57,28 +58,41 @@ struct trace_kfree_skb {
 	void *location;
 };
 
+struct meta {
+	int ifindex;
+	__u32 cb32_0;
+	__u8 cb8_0;
+};
+
 SEC("tp_btf/kfree_skb")
 int trace_kfree_skb(struct trace_kfree_skb *ctx)
 {
 	struct sk_buff *skb = ctx->skb;
 	struct net_device *dev;
-	int ifindex;
 	struct callback_head *ptr;
 	void *func;
 	int users;
 	unsigned char *data;
 	unsigned short pkt_data;
+	struct meta meta = {};
 	char pkt_type;
+	__u32 *cb32;
+	__u8 *cb8;
 
 	__builtin_preserve_access_index(({
 		users = skb->users.refs.counter;
 		data = skb->data;
 		dev = skb->dev;
-		ifindex = dev->ifindex;
 		ptr = dev->ifalias->rcuhead.next;
 		func = ptr->func;
+		cb8 = (__u8 *)&skb->cb;
+		cb32 = (__u32 *)&skb->cb;
 	}));
 
+	meta.ifindex = _(dev->ifindex);
+	meta.cb8_0 = cb8[8];
+	meta.cb32_0 = cb32[2];
+
 	bpf_probe_read_kernel(&pkt_type, sizeof(pkt_type), _(&skb->__pkt_type_offset));
 	pkt_type &= 7;
 
@@ -90,14 +104,15 @@ int trace_kfree_skb(struct trace_kfree_skb *ctx)
 		   _(skb->len), users, pkt_type);
 	bpf_printk("skb->queue_mapping %d\n", _(skb->queue_mapping));
 	bpf_printk("dev->ifindex %d data %llx pkt_data %x\n",
-		   ifindex, data, pkt_data);
+		   meta.ifindex, data, pkt_data);
+	bpf_printk("cb8_0:%x cb32_0:%x\n", meta.cb8_0, meta.cb32_0);
 
-	if (users != 1 || pkt_data != bpf_htons(0x86dd) || ifindex != 1)
+	if (users != 1 || pkt_data != bpf_htons(0x86dd) || meta.ifindex != 1)
 		/* raw tp ignores return value */
 		return 0;
 
 	/* send first 72 byte of the packet to user space */
 	bpf_skb_output(skb, &perf_buf_map, (72ull << 32) | BPF_F_CURRENT_CPU,
-		       &ifindex, sizeof(ifindex));
+		       &meta, sizeof(meta));
 	return 0;
 }