bpf: Add xdp dynptrs

Add xdp dynptrs, which are dynptrs whose underlying pointer points
to a xdp_buff. The dynptr acts on xdp data. xdp dynptrs have two main
benefits. One is that they allow operations on sizes that are not
statically known at compile-time (eg variable-sized accesses).
Another is that parsing the packet data through dynptrs (instead of
through direct access of xdp->data and xdp->data_end) can be more
ergonomic and less brittle (eg does not need manual if checking for
being within bounds of data_end).

For reads and writes on the dynptr, this includes reading/writing
from/to and across fragments. Data slices through the bpf_dynptr_data
API are not supported; instead bpf_dynptr_slice() and
bpf_dynptr_slice_rdwr() should be used.

For examples of how xdp dynptrs can be used, please see the attached
selftests.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Link: https://lore.kernel.org/r/20230301154953.641654-9-joannelkoong@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

3 files changed, 22 insertions, 2 deletions

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index e7436d7615b0..23ec684e660d 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -610,11 +610,15 @@ enum bpf_type_flag {
 	/* DYNPTR points to sk_buff */
 	DYNPTR_TYPE_SKB		= BIT(15 + BPF_BASE_TYPE_BITS),
 
+	/* DYNPTR points to xdp_buff */
+	DYNPTR_TYPE_XDP		= BIT(16 + BPF_BASE_TYPE_BITS),
+
 	__BPF_TYPE_FLAG_MAX,
 	__BPF_TYPE_LAST_FLAG	= __BPF_TYPE_FLAG_MAX - 1,
 };
 
-#define DYNPTR_TYPE_FLAG_MASK	(DYNPTR_TYPE_LOCAL | DYNPTR_TYPE_RINGBUF | DYNPTR_TYPE_SKB)
+#define DYNPTR_TYPE_FLAG_MASK	(DYNPTR_TYPE_LOCAL | DYNPTR_TYPE_RINGBUF | DYNPTR_TYPE_SKB \
+				 | DYNPTR_TYPE_XDP)
 
 /* Max number of base types. */
 #define BPF_BASE_TYPE_LIMIT	(1UL << BPF_BASE_TYPE_BITS)
@@ -1151,6 +1155,8 @@ enum bpf_dynptr_type {
 	BPF_DYNPTR_TYPE_RINGBUF,
 	/* Underlying data is a sk_buff */
 	BPF_DYNPTR_TYPE_SKB,
+	/* Underlying data is a xdp_buff */
+	BPF_DYNPTR_TYPE_XDP,
 };
 
 int bpf_dynptr_check_size(u32 size);
diff --git a/include/linux/filter.h b/include/linux/filter.h
index de18e844d15e..3f6992261ec5 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1546,6 +1546,8 @@ static __always_inline int __bpf_xdp_redirect_map(struct bpf_map *map, u64 index
 int __bpf_skb_load_bytes(const struct sk_buff *skb, u32 offset, void *to, u32 len);
 int __bpf_skb_store_bytes(struct sk_buff *skb, u32 offset, const void *from,
 			  u32 len, u64 flags);
+int __bpf_xdp_load_bytes(struct xdp_buff *xdp, u32 offset, void *buf, u32 len);
+int __bpf_xdp_store_bytes(struct xdp_buff *xdp, u32 offset, void *buf, u32 len);
 #else /* CONFIG_NET */
 static inline int __bpf_skb_load_bytes(const struct sk_buff *skb, u32 offset,
 				       void *to, u32 len)
@@ -1558,6 +1560,18 @@ static inline int __bpf_skb_store_bytes(struct sk_buff *skb, u32 offset,
 {
 	return -EOPNOTSUPP;
 }
+
+static inline int __bpf_xdp_load_bytes(struct xdp_buff *xdp, u32 offset,
+				       void *buf, u32 len)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline int __bpf_xdp_store_bytes(struct xdp_buff *xdp, u32 offset,
+					void *buf, u32 len)
+{
+	return -EOPNOTSUPP;
+}
 #endif /* CONFIG_NET */
 
 #endif /* __LINUX_FILTER_H__ */
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index d0351d30e551..faa304c926cf 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5344,7 +5344,7 @@ union bpf_attr {
  *		*len* must be a statically known value. The returned data slice
  *		is invalidated whenever the dynptr is invalidated.
  *
- *		skb type dynptrs may not use bpf_dynptr_data. They should
+ *		skb and xdp type dynptrs may not use bpf_dynptr_data. They should
  *		instead use bpf_dynptr_slice and bpf_dynptr_slice_rdwr.
  *	Return
  *		Pointer to the underlying dynptr data, NULL if the dynptr is