[PATCH v12 bpf-next 08/10] bpf: Add xdp dynptrs

Joanne Koong
2023-02-26T08:52:31Z

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>
---
include/linux/bpf.h | 8 +++++++-
include/linux/filter.h | 14 +++++++++++++
include/uapi/linux/bpf.h | 2 +-
kernel/bpf/helpers.c | 9 ++++++++-
kernel/bpf/verifier.c | 10 +++++++++
net/core/filter.c | 37 ++++++++++++++++++++++++++++++++--
tools/include/uapi/linux/bpf.h | 2 +-
7 files changed, 76 insertions(+), 6 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
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 1863bea0a21f..78fad0e84ca4 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1530,6 +1530,8 @@ BPF_CALL_5(bpf_dynptr_read, void *, dst, u32, len, const struct bpf_dynptr_kern
return 0;
case BPF_DYNPTR_TYPE_SKB:
return __bpf_skb_load_bytes(src->data, src->offset + offset, dst, len);
+ case BPF_DYNPTR_TYPE_XDP:
+ return __bpf_xdp_load_bytes(src->data, src->offset + offset, dst, len);
default:
WARN_ONCE(true, "bpf_dynptr_read: unknown dynptr type %d\n", type);
return -EFAULT;
@@ -1576,6 +1578,10 @@ BPF_CALL_5(bpf_dynptr_write, const struct bpf_dynptr_kern *, dst, u32, offset, v
case BPF_DYNPTR_TYPE_SKB:
return __bpf_skb_store_bytes(dst->data, dst->offset + offset, src, len,
flags);
+ case BPF_DYNPTR_TYPE_XDP:
+ if (flags)
+ return -EINVAL;
+ return __bpf_xdp_store_bytes(dst->data, dst->offset + offset, src, len);
default:
WARN_ONCE(true, "bpf_dynptr_write: unknown dynptr type %d\n", type);
return -EFAULT;
@@ -1615,7 +1621,8 @@ BPF_CALL_3(bpf_dynptr_data, const struct bpf_dynptr_kern *, ptr, u32, offset, u3
case BPF_DYNPTR_TYPE_RINGBUF:
return (unsigned long)(ptr->data + ptr->offset + offset);
case BPF_DYNPTR_TYPE_SKB:
- /* skb dynptrs should use bpf_dynptr_slice / bpf_dynptr_slice_rdwr */
+ case BPF_DYNPTR_TYPE_XDP:
+ /* skb and xdp dynptrs should use bpf_dynptr_slice / bpf_dynptr_slice_rdwr */
return 0;
default:
WARN_ONCE(true, "bpf_dynptr_data: unknown dynptr type %d\n", type);
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ef38ec52569a..cbb8c0178372 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -752,6 +752,8 @@ static enum bpf_dynptr_type arg_to_dynptr_type(enum bpf_arg_type arg_type)
return BPF_DYNPTR_TYPE_RINGBUF;
case DYNPTR_TYPE_SKB:
return BPF_DYNPTR_TYPE_SKB;
+ case DYNPTR_TYPE_XDP:
+ return BPF_DYNPTR_TYPE_XDP;
default:
return BPF_DYNPTR_TYPE_INVALID;
}
@@ -6300,6 +6302,9 @@ int process_dynptr_func(struct bpf_verifier_env *env, int regno, int insn_idx,
case DYNPTR_TYPE_SKB:
err_extra = "skb ";
break;
+ case DYNPTR_TYPE_XDP:
+ err_extra = "xdp ";
+ break;
default:
err_extra = "<unknown>";
break;
@@ -8943,6 +8948,7 @@ enum special_kfunc_type {
KF_bpf_rbtree_add,
KF_bpf_rbtree_first,
KF_bpf_dynptr_from_skb,
+ KF_bpf_dynptr_from_xdp,
};

BTF_SET_START(special_kfunc_set)
@@ -8958,6 +8964,7 @@ BTF_ID(func, bpf_rbtree_remove)
BTF_ID(func, bpf_rbtree_add)
BTF_ID(func, bpf_rbtree_first)
BTF_ID(func, bpf_dynptr_from_skb)
+BTF_ID(func, bpf_dynptr_from_xdp)
BTF_SET_END(special_kfunc_set)

BTF_ID_LIST(special_kfunc_list)
@@ -8975,6 +8982,7 @@ BTF_ID(func, bpf_rbtree_remove)
BTF_ID(func, bpf_rbtree_add)
BTF_ID(func, bpf_rbtree_first)
BTF_ID(func, bpf_dynptr_from_skb)
+BTF_ID(func, bpf_dynptr_from_xdp)

static bool is_kfunc_bpf_rcu_read_lock(struct bpf_kfunc_call_arg_meta *meta)
{
@@ -9731,6 +9739,8 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_

if (meta->func_id == special_kfunc_list[KF_bpf_dynptr_from_skb])
dynptr_arg_type |= DYNPTR_TYPE_SKB;
+ else if (meta->func_id == special_kfunc_list[KF_bpf_dynptr_from_xdp])
+ dynptr_arg_type |= DYNPTR_TYPE_XDP;

ret = process_dynptr_func(env, regno, insn_idx, dynptr_arg_type);
if (ret < 0)
diff --git a/net/core/filter.c b/net/core/filter.c
index f3afa31a9b10..c692046fa7f6 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3839,7 +3839,7 @@ static const struct bpf_func_proto sk_skb_change_head_proto = {
.arg3_type = ARG_ANYTHING,
};

-BPF_CALL_1(bpf_xdp_get_buff_len, struct xdp_buff*, xdp)
+BPF_CALL_1(bpf_xdp_get_buff_len, struct xdp_buff*, xdp)
{
return xdp_get_buff_len(xdp);
}
@@ -3999,6 +3999,11 @@ static const struct bpf_func_proto bpf_xdp_load_bytes_proto = {
.arg4_type = ARG_CONST_SIZE,
};

+int __bpf_xdp_load_bytes(struct xdp_buff *xdp, u32 offset, void *buf, u32 len)
+{
+ return ____bpf_xdp_load_bytes(xdp, offset, buf, len);
+}
+
BPF_CALL_4(bpf_xdp_store_bytes, struct xdp_buff *, xdp, u32, offset,
void *, buf, u32, len)
{
@@ -4026,6 +4031,11 @@ static const struct bpf_func_proto bpf_xdp_store_bytes_proto = {
.arg4_type = ARG_CONST_SIZE,
};

+int __bpf_xdp_store_bytes(struct xdp_buff *xdp, u32 offset, void *buf, u32 len)
+{
+ return ____bpf_xdp_store_bytes(xdp, offset, buf, len);
+}
+
static int bpf_xdp_frags_increase_tail(struct xdp_buff *xdp, int offset)
{
struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
@@ -11648,6 +11658,19 @@ __bpf_kfunc int bpf_dynptr_from_skb(struct sk_buff *skb, u64 flags,

return 0;
}
+
+__bpf_kfunc int bpf_dynptr_from_xdp(struct xdp_buff *xdp, u64 flags,
+ struct bpf_dynptr_kern *ptr__uninit)
+{
+ if (flags) {
+ bpf_dynptr_set_null(ptr__uninit);
+ return -EINVAL;
+ }
+
+ bpf_dynptr_init(ptr__uninit, xdp, BPF_DYNPTR_TYPE_XDP, 0, xdp_get_buff_len(xdp));
+
+ return 0;
+}
__diag_pop();

int bpf_dynptr_from_skb_rdonly(struct sk_buff *skb, u64 flags,
@@ -11668,11 +11691,20 @@ BTF_SET8_START(bpf_kfunc_check_set_skb)
BTF_ID_FLAGS(func, bpf_dynptr_from_skb)
BTF_SET8_END(bpf_kfunc_check_set_skb)

+BTF_SET8_START(bpf_kfunc_check_set_xdp)
+BTF_ID_FLAGS(func, bpf_dynptr_from_xdp)
+BTF_SET8_END(bpf_kfunc_check_set_xdp)
+
static const struct btf_kfunc_id_set bpf_kfunc_set_skb = {
.owner = THIS_MODULE,
.set = &bpf_kfunc_check_set_skb,
};

+static const struct btf_kfunc_id_set bpf_kfunc_set_xdp = {
+ .owner = THIS_MODULE,
+ .set = &bpf_kfunc_check_set_xdp,
+};
+
static int __init bpf_kfunc_init(void)
{
int ret;
@@ -11685,6 +11717,7 @@ static int __init bpf_kfunc_init(void)
ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_LWT_OUT, &bpf_kfunc_set_skb);
ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_LWT_IN, &bpf_kfunc_set_skb);
ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_LWT_XMIT, &bpf_kfunc_set_skb);
- return ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_LWT_SEG6LOCAL, &bpf_kfunc_set_skb);
+ ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_LWT_SEG6LOCAL, &bpf_kfunc_set_skb);
+ return ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP, &bpf_kfunc_set_xdp);
}
late_initcall(bpf_kfunc_init);
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index d0351d30e551..faa304c926cf 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/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
--
2.34.1