[PATCH 4/5] io_uring: bpf: add buffer support for IORING_OP_BPF

[Ming Lei <ming.lei@redhat.com>]

Add support for passing 0-2 buffers to BPF operations through
IORING_OP_BPF. Buffer types are encoded in sqe->bpf_op_flags
using dedicated 3-bit fields for each buffer.

Buffer 1 can be:
- None (no buffer)
- Plain user buffer (addr=sqe->addr, len=sqe->len)
- Fixed/registered buffer (index=sqe->buf_index, offset=sqe->addr,
  len=sqe->len)

Buffer 2 can be:
- None (no buffer)
- Plain user buffer (addr=sqe->addr3, len=sqe->optlen)

The sqe->bpf_op_flags layout (32 bits):
  Bits 31-24: BPF operation ID (8 bits)
  Bits 23-21: Buffer 1 type (3 bits)
  Bits 20-18: Buffer 2 type (3 bits)
  Bits 17-0:  Custom BPF flags (18 bits)

Using 3-bit encoding for each buffer type allows for future
expansion to 8 types (0-7). Currently types 0-2 are defined
(none/plain/fixed) and 3-7 are reserved for future use.

Buffer 2 currently only supports none/plain types because the
io_uring framework can only handle one fixed buffer per request
(via req->buf_index). The 3-bit encoding provides room for
future enhancements.

Buffer metadata (addresses, lengths) is stored in the extended
uring_bpf_data structure and is accessible to BPF programs with
readonly permissions. Buffer types can be extracted from the opf
field using IORING_BPF_BUF1_TYPE() and IORING_BPF_BUF2_TYPE()
macros.

Valid buffer combinations:
- 0 buffers
- 1 plain buffer
- 1 fixed buffer
- 2 plain buffers
- 1 fixed buffer + 1 plain buffer

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 include/uapi/linux/io_uring.h | 45 +++++++++++++++++++++++--
 io_uring/bpf.c                | 63 ++++++++++++++++++++++++++++++++++-
 io_uring/uring_bpf.h          | 12 ++++++-
 3 files changed, 116 insertions(+), 4 deletions(-)

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 94d2050131ac..950f4cfbbf86 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -429,12 +429,53 @@ enum io_uring_op {
 #define IORING_SEND_VECTORIZED		(1U << 5)
 
 /*
- * sqe->bpf_op_flags		top 8bits is for storing bpf op
- *				The other 24bits are used for bpf prog
+ * sqe->bpf_op_flags layout (32 bits total):
+ *   Bits 31-24: BPF operation ID (8 bits, 256 possible operations)
+ *   Bits 23-21: Buffer 1 type (3 bits: none/plain/fixed/reserved)
+ *   Bits 20-18: Buffer 2 type (3 bits: none/plain/reserved)
+ *   Bits 17-0:  Custom BPF flags (18 bits, available for BPF programs)
+ *
+ * For IORING_OP_BPF, buffers are specified as follows:
+ *   Buffer 1 (plain):  addr=sqe->addr, len=sqe->len
+ *   Buffer 1 (fixed):  index=sqe->buf_index, offset=sqe->addr, len=sqe->len
+ *   Buffer 2 (plain):  addr=sqe->addr3, len=sqe->optlen
+ *
+ * Note: Buffer 1 can be none/plain/fixed. Buffer 2 can only be none/plain.
+ *       3-bit encoding for each buffer allows for future expansion to 8 types (0-7).
+ *       Currently only one fixed buffer per request is supported (buffer 1).
+ *       Valid combinations: 0 buffers, 1 plain, 1 fixed, 2 plain, 1 fixed + 1 plain.
  */
 #define IORING_BPF_OP_BITS	(8)
 #define IORING_BPF_OP_SHIFT	(24)
 
+/* Buffer type encoding in sqe->bpf_op_flags */
+#define IORING_BPF_BUF1_TYPE_SHIFT	(21)
+#define IORING_BPF_BUF2_TYPE_SHIFT	(18)
+#define IORING_BPF_BUF_TYPE_NONE	(0)	/* No buffer */
+#define IORING_BPF_BUF_TYPE_PLAIN	(1)	/* Plain user buffer */
+#define IORING_BPF_BUF_TYPE_FIXED	(2)	/* Fixed/registered buffer */
+#define IORING_BPF_BUF_TYPE_MASK	(7)	/* 3-bit mask */
+
+/* Helper macros to encode/decode buffer types */
+#define IORING_BPF_BUF1_TYPE(flags) \
+	(((flags) >> IORING_BPF_BUF1_TYPE_SHIFT) & IORING_BPF_BUF_TYPE_MASK)
+#define IORING_BPF_BUF2_TYPE(flags) \
+	(((flags) >> IORING_BPF_BUF2_TYPE_SHIFT) & IORING_BPF_BUF_TYPE_MASK)
+#define IORING_BPF_SET_BUF1_TYPE(type) \
+	(((type) & IORING_BPF_BUF_TYPE_MASK) << IORING_BPF_BUF1_TYPE_SHIFT)
+#define IORING_BPF_SET_BUF2_TYPE(type) \
+	(((type) & IORING_BPF_BUF_TYPE_MASK) << IORING_BPF_BUF2_TYPE_SHIFT)
+
+/* Custom BPF flags mask (18 bits available, bits 17-0) */
+#define IORING_BPF_CUSTOM_FLAGS_MASK	((1U << 18) - 1)
+
+/* Encode all components into sqe->bpf_op_flags */
+#define IORING_BPF_OP_FLAGS(op, buf1_type, buf2_type, flags) \
+	(((op) << IORING_BPF_OP_SHIFT) | \
+	 IORING_BPF_SET_BUF1_TYPE(buf1_type) | \
+	 IORING_BPF_SET_BUF2_TYPE(buf2_type) | \
+	 ((flags) & IORING_BPF_CUSTOM_FLAGS_MASK))
+
 /*
  * cqe.res for IORING_CQE_F_NOTIF if
  * IORING_SEND_ZC_REPORT_USAGE was requested
diff --git a/io_uring/bpf.c b/io_uring/bpf.c
index 8227be6d5a10..e837c3d57b96 100644
--- a/io_uring/bpf.c
+++ b/io_uring/bpf.c
@@ -11,8 +11,10 @@
 #include <linux/btf.h>
 #include <linux/btf_ids.h>
 #include <linux/filter.h>
+#include <linux/uio.h>
 #include "io_uring.h"
 #include "uring_bpf.h"
+#include "rsrc.h"
 
 #define MAX_BPF_OPS_COUNT	(1 << IORING_BPF_OP_BITS)
 
@@ -28,7 +30,7 @@ static inline unsigned char uring_bpf_get_op(unsigned int op_flags)
 
 static inline unsigned int uring_bpf_get_flags(unsigned int op_flags)
 {
-	return op_flags & ((1U << IORING_BPF_OP_SHIFT) - 1);
+	return op_flags & IORING_BPF_CUSTOM_FLAGS_MASK;
 }
 
 static inline struct uring_bpf_ops *uring_bpf_get_ops(struct uring_bpf_data *data)
@@ -36,18 +38,77 @@ static inline struct uring_bpf_ops *uring_bpf_get_ops(struct uring_bpf_data *dat
 	return &bpf_ops[uring_bpf_get_op(data->opf)];
 }
 
+static int io_bpf_prep_buffers(struct io_kiocb *req,
+			       const struct io_uring_sqe *sqe,
+			       struct uring_bpf_data *data,
+			       unsigned int op_flags)
+{
+	u8 buf1_type, buf2_type;
+
+	/* Extract buffer configuration from bpf_op_flags */
+	buf1_type = IORING_BPF_BUF1_TYPE(op_flags);
+	buf2_type = IORING_BPF_BUF2_TYPE(op_flags);
+
+	/* Prepare buffer 1 */
+	if (buf1_type == IORING_BPF_BUF_TYPE_PLAIN) {
+		/* Plain user buffer: addr=sqe->addr, len=sqe->len */
+		data->buf1_addr = READ_ONCE(sqe->addr);
+		data->buf1_len = READ_ONCE(sqe->len);
+	} else if (buf1_type == IORING_BPF_BUF_TYPE_FIXED) {
+		/* Fixed buffer: index=sqe->buf_index, offset=sqe->addr, len=sqe->len */
+		req->buf_index = READ_ONCE(sqe->buf_index);
+		data->buf1_addr = READ_ONCE(sqe->addr);  /* offset within fixed buffer */
+		data->buf1_len = READ_ONCE(sqe->len);
+
+		/* Validate buffer index */
+		if (unlikely(!req->ctx->buf_table.nr))
+			return -EFAULT;
+		if (unlikely(req->buf_index >= req->ctx->buf_table.nr))
+			return -EINVAL;
+	} else if (buf1_type == IORING_BPF_BUF_TYPE_NONE) {
+		data->buf1_addr = 0;
+		data->buf1_len = 0;
+	} else {
+		return -EINVAL;
+	}
+
+	/* Prepare buffer 2 (plain only - io_uring only supports one fixed buffer) */
+	if (buf2_type == IORING_BPF_BUF_TYPE_PLAIN) {
+		/* Plain user buffer: addr=sqe->addr3, len=sqe->optlen */
+		data->buf2_addr = READ_ONCE(sqe->addr3);
+		data->buf2_len = READ_ONCE(sqe->optlen);
+	} else if (buf2_type == IORING_BPF_BUF_TYPE_NONE) {
+		data->buf2_addr = 0;
+		data->buf2_len = 0;
+	} else {
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+
 int io_uring_bpf_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
 	struct uring_bpf_data *data = io_kiocb_to_cmd(req, struct uring_bpf_data);
 	unsigned int op_flags = READ_ONCE(sqe->bpf_op_flags);
 	struct uring_bpf_ops *ops;
+	int ret;
 
 	if (!(req->ctx->flags & IORING_SETUP_BPF))
 		return -EACCES;
 
+	if (uring_bpf_get_flags(op_flags))
+		return -EINVAL;
+
 	data->opf = op_flags;
 	ops = &bpf_ops[uring_bpf_get_op(data->opf)];
 
+	/* Prepare buffers based on buffer type flags */
+	ret = io_bpf_prep_buffers(req, sqe, data, op_flags);
+	if (ret)
+		return ret;
+
 	if (ops->prep_fn)
 		return ops->prep_fn(data, sqe);
 	return -EOPNOTSUPP;
diff --git a/io_uring/uring_bpf.h b/io_uring/uring_bpf.h
index c76eba887d22..c919931cb4b0 100644
--- a/io_uring/uring_bpf.h
+++ b/io_uring/uring_bpf.h
@@ -7,8 +7,18 @@ struct uring_bpf_data {
 	struct file     *file;
 	u32		opf;
 
+	/* Buffer 1 metadata - readable for bpf prog */
+	u32		buf1_len;		/* buffer 1 length, bytes 12-15 */
+	u64		buf1_addr;		/* buffer 1 address or offset, bytes 16-23 */
+
+	/* Buffer 2 metadata - readable for bpf prog (plain only) */
+	u64		buf2_addr;		/* buffer 2 address, bytes 24-31 */
+	u32		buf2_len;		/* buffer 2 length, bytes 32-35 */
+	u32		__pad;			/* padding, bytes 36-39 */
+
 	/* writeable for bpf prog */
-	u8              pdu[64 - sizeof(struct file *) - sizeof(u32)];
+	u8              pdu[64 - sizeof(struct file *) - 4 * sizeof(u32) -
+		2 * sizeof(u64)];
 };
 
 typedef int (*uring_io_prep_t)(struct uring_bpf_data *data,
-- 
2.47.0