On 11/3/22 8:25 PM, Stanislav Fomichev wrote:
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 59c9fd55699d..dba857f212d7 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -4217,9 +4217,13 @@ static inline bool skb_metadata_differs(const struct sk_buff *skb_a,
true : __skb_metadata_differs(skb_a, skb_b, len_a);
}
+void skb_metadata_import_from_xdp(struct sk_buff *skb, size_t len);
+
static inline void skb_metadata_set(struct sk_buff *skb, u8 meta_len)
{
skb_shinfo(skb)->meta_len = meta_len;
+ if (meta_len)
+ skb_metadata_import_from_xdp(skb, meta_len);
}
[ ... ]
+struct xdp_to_skb_metadata {
+ u32 magic; /* xdp_metadata_magic */
+ u64 rx_timestamp;
+} __randomize_layout;
+
+struct bpf_patch;
+
[ ... ]
+void skb_metadata_import_from_xdp(struct sk_buff *skb, size_t len)
+{
+ struct xdp_to_skb_metadata *meta = (void *)(skb_mac_header(skb) - len);
+
+ /* Optional SKB info, currently missing:
+ * - HW checksum info (skb->ip_summed)
+ * - HW RX hash (skb_set_hash)
+ * - RX ring dev queue index (skb_record_rx_queue)
+ */
+
+ if (len != sizeof(struct xdp_to_skb_metadata))
+ return;
+
+ if (meta->magic != xdp_metadata_magic)
+ return;
+
+ if (meta->rx_timestamp) {
+ *skb_hwtstamps(skb) = (struct skb_shared_hwtstamps){
+ .hwtstamp = ns_to_ktime(meta->rx_timestamp),
+ };
+ }
+}
Considering the metadata will affect the gro, should the meta be cleared after
importing to the skb?
[ ... ]
+/* Since we're not actually doing a call but instead rewriting
+ * in place, we can only afford to use R0-R5 scratch registers.
+ *
+ * We reserve R1 for bpf_xdp_metadata_export_to_skb and let individual
+ * metadata kfuncs use only R0,R4-R5.
+ *
+ * The above also means we _cannot_ easily call any other helper/kfunc
+ * because there is no place for us to preserve our R1 argument;
+ * existing R6-R9 belong to the callee.
+ */
+void xdp_metadata_export_to_skb(const struct bpf_prog *prog, struct bpf_patch *patch)
+{
+ u32 func_id;
+
+ /*
+ * The code below generates the following:
+ *
+ * void bpf_xdp_metadata_export_to_skb(struct xdp_md *ctx)
+ * {
+ * struct xdp_to_skb_metadata *meta;
+ * int ret;
+ *
+ * ret = bpf_xdp_adjust_meta(ctx, -sizeof(*meta));
+ * if (!ret)
+ * return;
+ *
+ * meta = ctx->data_meta;
+ * meta->magic = xdp_metadata_magic;
+ * meta->rx_timestamp = bpf_xdp_metadata_rx_timestamp(ctx);
+ * }
+ *
+ */
+
+ bpf_patch_append(patch,
+ /* r2 = ((struct xdp_buff *)r1)->data_meta; */
+ BPF_LDX_MEM(BPF_DW, BPF_REG_2, BPF_REG_1,
+ offsetof(struct xdp_buff, data_meta)),
+ /* r3 = ((struct xdp_buff *)r1)->data; */
+ BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_1,
+ offsetof(struct xdp_buff, data)),
+ /* if (data_meta != data) return;
+ *
+ * data_meta > data: xdp_data_meta_unsupported()
+ * data_meta < data: already used, no need to touch
+ */
+ BPF_JMP_REG(BPF_JNE, BPF_REG_2, BPF_REG_3, S16_MAX),
+
+ /* r2 -= sizeof(struct xdp_to_skb_metadata); */
+ BPF_ALU64_IMM(BPF_SUB, BPF_REG_2,
+ sizeof(struct xdp_to_skb_metadata)),
+ /* r3 = ((struct xdp_buff *)r1)->data_hard_start; */
+ BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_1,
+ offsetof(struct xdp_buff, data_hard_start)),
+ /* r3 += sizeof(struct xdp_frame) */
+ BPF_ALU64_IMM(BPF_ADD, BPF_REG_3,
+ sizeof(struct xdp_frame)),
+ /* if (data-sizeof(struct xdp_to_skb_metadata) < data_hard_start+sizeof(struct xdp_frame)) return; */
+ BPF_JMP_REG(BPF_JLT, BPF_REG_2, BPF_REG_3, S16_MAX),
+
+ /* ((struct xdp_buff *)r1)->data_meta = r2; */
+ BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_2,
+ offsetof(struct xdp_buff, data_meta)),
+
+ /* *((struct xdp_to_skb_metadata *)r2)->magic = xdp_metadata_magic; */
+ BPF_ST_MEM(BPF_W, BPF_REG_2,
+ offsetof(struct xdp_to_skb_metadata, magic),
+ xdp_metadata_magic),
+ );
+
+ /* r0 = bpf_xdp_metadata_rx_timestamp(ctx); */
+ func_id = xdp_metadata_kfunc_id(XDP_METADATA_KFUNC_RX_TIMESTAMP);
+ prog->aux->xdp_kfunc_ndo->ndo_unroll_kfunc(prog, func_id, patch);
+
+ bpf_patch_append(patch,
+ /* r2 = ((struct xdp_buff *)r1)->data_meta; */
+ BPF_LDX_MEM(BPF_DW, BPF_REG_2, BPF_REG_1,
+ offsetof(struct xdp_buff, data_meta)),
+ /* *((struct xdp_to_skb_metadata *)r2)->rx_timestamp = r0; */
+ BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_0,
+ offsetof(struct xdp_to_skb_metadata, rx_timestamp)),
Can the xdp prog still change the metadata through xdp->data_meta? tbh, I am not
sure it is solid enough by asking the xdp prog not to use the same random number
in its own metadata + not to change the metadata through xdp->data_meta after
calling bpf_xdp_metadata_export_to_skb().
Does xdp_to_skb_metadata have a use case for XDP_PASS (like patch 7) or the
xdp_to_skb_metadata can be limited to XDP_REDIRECT only?
+ );
+
+ bpf_patch_resolve_jmp(patch);
+}
+
static int __init xdp_metadata_init(void)
{
+ xdp_metadata_magic = get_random_u32() | 1;
return register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP, &xdp_metadata_kfunc_set);
}
late_initcall(xdp_metadata_init);
