unstable xdp tests. Was: [PATCH net-next v4 31/33] 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 <redacted>
---
 net/bpf/test_run.c |   16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index 29dbdd4c29f6..30ba7d38941d 100644
--- a/net/bpf/test_run.c
+++ b/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);