bpf: Add xdp.frame_sz in bpf_prog_test_run_xdp().

Update the memory requirements, when adding xdp.frame_sz in BPF test_run
function bpf_prog_test_run_xdp() which e.g. is used by XDP selftests.

Specifically add the expected reserved tailroom, but also allocated a
larger memory area to reflect that XDP frames usually comes in this
format. Limit the provided packet data size to 4096 minus headroom +
tailroom, as this also reflect a common 3520 bytes MTU limit with XDP.

Note that bpf_test_init already use a memory allocation method that clears
memory.  Thus, this already guards against leaking uninit kernel memory.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/158945349549.97035.15316291762482444006.stgit@firesoul

net/bpf/test_run.c

@@ -470,25 +470,34 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
 int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
 			  union bpf_attr __user *uattr)
 {
+	u32 tailroom = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+	u32 headroom = XDP_PACKET_HEADROOM;
 	u32 size = kattr->test.data_size_in;
 	u32 repeat = kattr->test.repeat;
 	struct netdev_rx_queue *rxqueue;
 	struct xdp_buff xdp = {};
 	u32 retval, duration;
+	u32 max_data_sz;
 	void *data;
 	int ret;
 
 	if (kattr->test.ctx_in || kattr->test.ctx_out)
 		return -EINVAL;
 
-	data = bpf_test_init(kattr, size, XDP_PACKET_HEADROOM + NET_IP_ALIGN, 0);
+	/* XDP have extra tailroom as (most) drivers use full page */
+	max_data_sz = 4096 - headroom - tailroom;
+	if (size > max_data_sz)
+		return -EINVAL;
+
+	data = bpf_test_init(kattr, max_data_sz, headroom, tailroom);
 	if (IS_ERR(data))
 		return PTR_ERR(data);
 
 	xdp.data_hard_start = data;
-	xdp.data = data + XDP_PACKET_HEADROOM + NET_IP_ALIGN;
+	xdp.data = data + headroom;
 	xdp.data_meta = xdp.data;
 	xdp.data_end = xdp.data + size;
+	xdp.frame_sz = headroom + max_data_sz + tailroom;
 
 	rxqueue = __netif_get_rx_queue(current->nsproxy->net_ns->loopback_dev, 0);
 	xdp.rxq = &rxqueue->xdp_rxq;
@@ -496,8 +505,7 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
 	ret = bpf_test_run(prog, &xdp, repeat, &retval, &duration, true);
 	if (ret)
 		goto out;
-	if (xdp.data != data + XDP_PACKET_HEADROOM + NET_IP_ALIGN ||
-	    xdp.data_end != xdp.data + size)
+	if (xdp.data != data + headroom || xdp.data_end != xdp.data + size)
 		size = xdp.data_end - xdp.data;
 	ret = bpf_test_finish(kattr, uattr, xdp.data, size, retval, duration);
 out: