[PATCH v15 bpf-next 17/18] net: xdp: introduce bpf_xdp_pointer utility routine

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Similar to skb_header_pointer, introduce bpf_xdp_pointer utility routine
to return a pointer to a given position in the xdp_buff if the requested
area (offset + len) is contained in a contiguous memory area otherwise it
will be copied in a bounce buffer provided by the caller.
Similar to the tc counterpart, introduce the two following xdp helpers:
- bpf_xdp_load_bytes
- bpf_xdp_store_bytes

Signed-off-by: Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
---
 include/uapi/linux/bpf.h       |  18 +++++
 net/core/filter.c              | 127 +++++++++++++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h |  18 +++++
 3 files changed, 163 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index a9946d860740..0a56e7e0700b 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4915,6 +4915,22 @@ union bpf_attr {
  *		Get the total size of a given xdp buff (linear and paged area)
  *	Return
  *		The total size of a given xdp buffer.
+ *
+ * long bpf_xdp_load_bytes(struct xdp_buff *xdp_md, u32 offset, void *buf, u32 len)
+ *	Description
+ *		This helper is provided as an easy way to load data from a
+ *		xdp buffer. It can be used to load *len* bytes from *offset* from
+ *		the frame associated to *xdp_md*, into the buffer pointed by
+ *		*buf*.
+ *	Return
+ *		0 on success, or a negative error in case of failure.
+ *
+ * long bpf_xdp_store_bytes(struct xdp_buff *xdp_md, u32 offset, void *buf, u32 len)
+ *	Description
+ *		Store *len* bytes from buffer *buf* into the frame
+ *		associated to *xdp_md*, at *offset*.
+ *	Return
+ *		0 on success, or a negative error in case of failure.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -5096,6 +5112,8 @@ union bpf_attr {
 	FN(get_branch_snapshot),	\
 	FN(trace_vprintk),		\
 	FN(xdp_get_buff_len),		\
+	FN(xdp_load_bytes),		\
+	FN(xdp_store_bytes),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/net/core/filter.c b/net/core/filter.c
index 79c2b71b96e0..07d8fb680991 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3848,6 +3848,129 @@ static const struct bpf_func_proto bpf_xdp_adjust_head_proto = {
 	.arg2_type	= ARG_ANYTHING,
 };
 
+static void bpf_xdp_copy_buf(struct xdp_buff *xdp, u32 offset,
+			     u32 len, void *buf, bool flush)
+{
+	struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
+	u32 headsize = xdp->data_end - xdp->data;
+	u32 count = 0, frame_offset = headsize;
+	int i = 0;
+
+	if (offset < headsize) {
+		int size = min_t(int, headsize - offset, len);
+		void *src = flush ? buf : xdp->data + offset;
+		void *dst = flush ? xdp->data + offset : buf;
+
+		memcpy(dst, src, size);
+		count = size;
+		offset = 0;
+	}
+
+	while (count < len && i < sinfo->nr_frags) {
+		skb_frag_t *frag = &sinfo->frags[i++];
+		u32 frag_size = skb_frag_size(frag);
+
+		if  (offset < frame_offset + frag_size) {
+			int size = min_t(int, frag_size - offset, len - count);
+			void *addr = skb_frag_address(frag);
+			void *src = flush ? buf + count : addr + offset;
+			void *dst = flush ? addr + offset : buf + count;
+
+			memcpy(dst, src, size);
+			count += size;
+			offset = 0;
+		}
+		frame_offset += frag_size;
+	}
+}
+
+static void *bpf_xdp_pointer(struct xdp_buff *xdp, u32 offset,
+			     u32 len, void *buf)
+{
+	struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
+	u32 size = xdp->data_end - xdp->data;
+	void *addr = xdp->data;
+	int i;
+
+	if (offset < size) /* linear area */
+		goto out;
+
+	offset -= size;
+	for (i = 0; i < sinfo->nr_frags; i++) { /* paged area */
+		u32 frag_size = skb_frag_size(&sinfo->frags[i]);
+
+		if  (offset < frag_size) {
+			addr = skb_frag_address(&sinfo->frags[i]);
+			size = frag_size;
+			break;
+		}
+		offset -= frag_size;
+	}
+
+out:
+	if (offset + len < size)
+		return addr + offset; /* fast path - no need to copy */
+
+	if (!buf) /* no copy to the bounce buffer */
+		return NULL;
+
+	/* slow path - we need to copy data into the bounce buffer */
+	bpf_xdp_copy_buf(xdp, offset, len, buf, false);
+	return buf;
+}
+
+BPF_CALL_4(bpf_xdp_load_bytes, struct xdp_buff *, xdp, u32, offset,
+	   void *, buf, u32, len)
+{
+	void *ptr;
+
+	if (!buf)
+		return -EINVAL;
+
+	ptr = bpf_xdp_pointer(xdp, offset, len, buf);
+	if (ptr != buf)
+		memcpy(buf, ptr, len);
+
+	return 0;
+}
+
+static const struct bpf_func_proto bpf_xdp_load_bytes_proto = {
+	.func		= bpf_xdp_load_bytes,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_CTX,
+	.arg2_type	= ARG_ANYTHING,
+	.arg3_type	= ARG_PTR_TO_UNINIT_MEM,
+	.arg4_type	= ARG_CONST_SIZE,
+};
+
+BPF_CALL_4(bpf_xdp_store_bytes, struct xdp_buff *, xdp, u32, offset,
+	   void *, buf, u32, len)
+{
+	void *ptr;
+
+	if (!buf)
+		return -EINVAL;
+
+	ptr = bpf_xdp_pointer(xdp, offset, len, NULL);
+	if (!ptr)
+		bpf_xdp_copy_buf(xdp, offset, len, buf, true);
+	else
+		memcpy(ptr, buf, len);
+
+	return 0;
+}
+
+static const struct bpf_func_proto bpf_xdp_store_bytes_proto = {
+	.func		= bpf_xdp_store_bytes,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_CTX,
+	.arg2_type	= ARG_ANYTHING,
+	.arg3_type	= ARG_PTR_TO_UNINIT_MEM,
+	.arg4_type	= ARG_CONST_SIZE,
+};
+
 static int bpf_xdp_mb_increase_tail(struct xdp_buff *xdp, int offset)
 {
 	struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
@@ -7619,6 +7742,10 @@ xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_xdp_adjust_tail_proto;
 	case BPF_FUNC_xdp_get_buff_len:
 		return &bpf_xdp_get_buff_len_proto;
+	case BPF_FUNC_xdp_load_bytes:
+		return &bpf_xdp_load_bytes_proto;
+	case BPF_FUNC_xdp_store_bytes:
+		return &bpf_xdp_store_bytes_proto;
 	case BPF_FUNC_fib_lookup:
 		return &bpf_xdp_fib_lookup_proto;
 	case BPF_FUNC_check_mtu:
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index a9946d860740..0a56e7e0700b 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4915,6 +4915,22 @@ union bpf_attr {
  *		Get the total size of a given xdp buff (linear and paged area)
  *	Return
  *		The total size of a given xdp buffer.
+ *
+ * long bpf_xdp_load_bytes(struct xdp_buff *xdp_md, u32 offset, void *buf, u32 len)
+ *	Description
+ *		This helper is provided as an easy way to load data from a
+ *		xdp buffer. It can be used to load *len* bytes from *offset* from
+ *		the frame associated to *xdp_md*, into the buffer pointed by
+ *		*buf*.
+ *	Return
+ *		0 on success, or a negative error in case of failure.
+ *
+ * long bpf_xdp_store_bytes(struct xdp_buff *xdp_md, u32 offset, void *buf, u32 len)
+ *	Description
+ *		Store *len* bytes from buffer *buf* into the frame
+ *		associated to *xdp_md*, at *offset*.
+ *	Return
+ *		0 on success, or a negative error in case of failure.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -5096,6 +5112,8 @@ union bpf_attr {
 	FN(get_branch_snapshot),	\
 	FN(trace_vprintk),		\
 	FN(xdp_get_buff_len),		\
+	FN(xdp_load_bytes),		\
+	FN(xdp_store_bytes),		\
 	/* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
-- 
2.31.1




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