[PATCH bpf-next] bpf: better availability probing for seg6 helpers

[Mathieu Xhonneux]

bpf_lwt_seg6_* helpers require CONFIG_IPV6_SEG6_BPF, and currently
return -EOPNOTSUPP to indicate unavailability. This patch forces the
BPF verifier to reject programs using these helpers when
!CONFIG_IPV6_SEG6_BPF, allowing users to more easily probe if they are
available or not.

Signed-off-by: Mathieu Xhonneux <m.xhonn...@gmail.com>
---
 net/core/filter.c | 22 ++++++++--------------
 1 file changed, 8 insertions(+), 14 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index b9ec916f4e3a..c910a95e9a7c 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4439,10 +4439,10 @@ static const struct bpf_func_proto 
bpf_lwt_push_encap_proto = {
        .arg4_type      = ARG_CONST_SIZE
 };
 
+#if IS_ENABLED(CONFIG_IPV6_SEG6_BPF)
 BPF_CALL_4(bpf_lwt_seg6_store_bytes, struct sk_buff *, skb, u32, offset,
           const void *, from, u32, len)
 {
-#if IS_ENABLED(CONFIG_IPV6_SEG6_BPF)
        struct seg6_bpf_srh_state *srh_state =
                this_cpu_ptr(&seg6_bpf_srh_states);
        void *srh_tlvs, *srh_end, *ptr;
@@ -4468,9 +4468,6 @@ BPF_CALL_4(bpf_lwt_seg6_store_bytes, struct sk_buff *, 
skb, u32, offset,
 
        memcpy(skb->data + offset, from, len);
        return 0;
-#else /* CONFIG_IPV6_SEG6_BPF */
-       return -EOPNOTSUPP;
-#endif
 }
 
 static const struct bpf_func_proto bpf_lwt_seg6_store_bytes_proto = {
@@ -4486,7 +4483,6 @@ static const struct bpf_func_proto 
bpf_lwt_seg6_store_bytes_proto = {
 BPF_CALL_4(bpf_lwt_seg6_action, struct sk_buff *, skb,
           u32, action, void *, param, u32, param_len)
 {
-#if IS_ENABLED(CONFIG_IPV6_SEG6_BPF)
        struct seg6_bpf_srh_state *srh_state =
                this_cpu_ptr(&seg6_bpf_srh_states);
        struct ipv6_sr_hdr *srh;
@@ -4534,9 +4530,6 @@ BPF_CALL_4(bpf_lwt_seg6_action, struct sk_buff *, skb,
        default:
                return -EINVAL;
        }
-#else /* CONFIG_IPV6_SEG6_BPF */
-       return -EOPNOTSUPP;
-#endif
 }
 
 static const struct bpf_func_proto bpf_lwt_seg6_action_proto = {
@@ -4552,7 +4545,6 @@ static const struct bpf_func_proto 
bpf_lwt_seg6_action_proto = {
 BPF_CALL_3(bpf_lwt_seg6_adjust_srh, struct sk_buff *, skb, u32, offset,
           s32, len)
 {
-#if IS_ENABLED(CONFIG_IPV6_SEG6_BPF)
        struct seg6_bpf_srh_state *srh_state =
                this_cpu_ptr(&seg6_bpf_srh_states);
        void *srh_end, *srh_tlvs, *ptr;
@@ -4596,9 +4588,6 @@ BPF_CALL_3(bpf_lwt_seg6_adjust_srh, struct sk_buff *, 
skb, u32, offset,
        srh_state->hdrlen += len;
        srh_state->valid = 0;
        return 0;
-#else /* CONFIG_IPV6_SEG6_BPF */
-       return -EOPNOTSUPP;
-#endif
 }
 
 static const struct bpf_func_proto bpf_lwt_seg6_adjust_srh_proto = {
@@ -4609,6 +4598,7 @@ static const struct bpf_func_proto 
bpf_lwt_seg6_adjust_srh_proto = {
        .arg2_type      = ARG_ANYTHING,
        .arg3_type      = ARG_ANYTHING,
 };
+#endif /* CONFIG_IPV6_SEG6_BPF */
 
 bool bpf_helper_changes_pkt_data(void *func)
 {
@@ -4627,10 +4617,12 @@ bool bpf_helper_changes_pkt_data(void *func)
            func == bpf_xdp_adjust_meta ||
            func == bpf_msg_pull_data ||
            func == bpf_xdp_adjust_tail ||
-           func == bpf_lwt_push_encap ||
+#if IS_ENABLED(CONFIG_IPV6_SEG6_BPF)
            func == bpf_lwt_seg6_store_bytes ||
            func == bpf_lwt_seg6_adjust_srh ||
-           func == bpf_lwt_seg6_action
+           func == bpf_lwt_seg6_action ||
+#endif
+           func == bpf_lwt_push_encap
            )
                return true;
 
@@ -4967,12 +4959,14 @@ static const struct bpf_func_proto *
 lwt_seg6local_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
        switch (func_id) {
+#if IS_ENABLED(CONFIG_IPV6_SEG6_BPF)
        case BPF_FUNC_lwt_seg6_store_bytes:
                return &bpf_lwt_seg6_store_bytes_proto;
        case BPF_FUNC_lwt_seg6_action:
                return &bpf_lwt_seg6_action_proto;
        case BPF_FUNC_lwt_seg6_adjust_srh:
                return &bpf_lwt_seg6_adjust_srh_proto;
+#endif
        default:
                return lwt_out_func_proto(func_id, prog);
        }
-- 
2.16.1