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bpf: Add xdp dynptrs

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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>
This commit is contained in:
Joanne Koong 2023-03-01 07:49:51 -08:00 • committed by Alexei Starovoitov
parent b5964b968a
commit 05421aecd4
7 changed files with 76 additions and 6 deletions
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8
include/linux/bpf.h
View file

@ -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);