On Fri, 1 Jun 2018 14:15:58 +0200
Sebastiano Miano via iovisor-dev <[email protected]> wrote:
> Dear all,
>
> We have noticed that the bpf_redirect_map returns an error when it is
> called after a tail call.
> The xdp_redirect_map program (under sample/bpf) works fine, but if we
> modify it as shown in the following diff, it doesn't work anymore.
> I have debugged it with the xdp_monitor application and the error
> returned is EFAULT.
> Is this a known issue? Am I doing something wrong?
Argh, this is likely an issue/bug due to the check xdp_map_invalid(),
that was introduced in commit 7c3001313396 ("bpf: fix ri->map_owner
pointer on bpf_prog_realloc").
To Daniel, I don't know how to solve this, could you give some advice?
static inline bool xdp_map_invalid(const struct bpf_prog *xdp_prog,
unsigned long aux)
{
return (unsigned long)xdp_prog->aux != aux;
}
static int xdp_do_redirect_map(struct net_device *dev, struct xdp_buff *xdp,
struct bpf_prog *xdp_prog)
{
struct redirect_info *ri = this_cpu_ptr(&redirect_info);
unsigned long map_owner = ri->map_owner;
struct bpf_map *map = ri->map;
u32 index = ri->ifindex;
void *fwd = NULL;
int err;
[...]
if (unlikely(xdp_map_invalid(xdp_prog, map_owner))) {
err = -EFAULT;
map = NULL;
goto err;
}
[...]
> P.S. I have tested the program with the latest bpf-next kernel.
>
> ------------
>
> diff --git a/samples/bpf/xdp_redirect_map_kern.c
> b/samples/bpf/xdp_redirect_map_kern.c
> index 740a529..bf1275a 100644
> --- a/samples/bpf/xdp_redirect_map_kern.c
> +++ b/samples/bpf/xdp_redirect_map_kern.c
> @@ -36,6 +36,13 @@ struct bpf_map_def SEC("maps") rxcnt = {
> .max_entries = 1,
> };
>
> +struct bpf_map_def SEC("maps") prog_table = {
> + .type = BPF_MAP_TYPE_PROG_ARRAY,
> + .key_size = sizeof(int),
> + .value_size = sizeof(int),
> + .max_entries = 32,
> +};
> +
> static void swap_src_dst_mac(void *data)
> {
> unsigned short *p = data;
> @@ -89,4 +96,15 @@ int xdp_redirect_dummy_prog(struct xdp_md *ctx)
> return XDP_PASS;
> }
>
> +/* Entry point */
> +SEC("xdp_redirect_entry_point")
> +int xdp_redirect_entry_point_prog(struct xdp_md *ctx)
> +{
> + //char fmt[] = "xdp_redirect_entry_point\n";
> + //bpf_trace_printk(fmt, sizeof(fmt));
> + bpf_tail_call(ctx, &prog_table, 0);
> + // Tail call failed
> + return XDP_DROP;
> +}
> +
> char _license[] SEC("license") = "GPL";
> diff --git a/samples/bpf/xdp_redirect_map_user.c
> b/samples/bpf/xdp_redirect_map_user.c
> index 4445e76..b2d2059 100644
> --- a/samples/bpf/xdp_redirect_map_user.c
> +++ b/samples/bpf/xdp_redirect_map_user.c
> @@ -120,7 +120,13 @@ int main(int argc, char **argv)
> return 1;
> }
>
> - if (bpf_set_link_xdp_fd(ifindex_in, prog_fd[0], xdp_flags) < 0) {
> + ret = bpf_map_update_elem(map_fd[2], &key, &prog_fd[0], 0);
> + if (ret) {
> + perror("bpf_update_elem");
> + goto out;
> + }
> +
> + if (bpf_set_link_xdp_fd(ifindex_in, prog_fd[2], xdp_flags) < 0) {
> printf("ERROR: link set xdp fd failed on %d\n", ifindex_in);
> return 1;
> }
> _______________________________________________
> iovisor-dev mailing list
> [email protected]
> https://lists.iovisor.org/mailman/listinfo/iovisor-dev
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
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