Expose existing 'bpf_xdp_pointer' as a BPF helper named 'bpf_packet_pointer'
returning a packet pointer with a fixed immutable range. This can be useful to
enable DPA without having to use memcpy (currently the case in
bpf_xdp_load_bytes and bpf_xdp_store_bytes).
The intended usage to read and write data for multi-buff XDP is:
int err = 0;
char buf[N];
off &= 0xffff;
ptr = bpf_packet_pointer(ctx, off, sizeof(buf), &err);
if (unlikely(!ptr)) {
if (err < 0)
return XDP_ABORTED;
err = bpf_xdp_load_bytes(ctx, off, buf, sizeof(buf));
if (err < 0)
return XDP_ABORTED;
ptr = buf;
}
...
// Do some stores and loads in [ptr, ptr + N) region
...
if (unlikely(ptr == buf)) {
err = bpf_xdp_store_bytes(ctx, off, buf, sizeof(buf));
if (err < 0)
return XDP_ABORTED;
}
Note that bpf_packet_pointer returns a PTR_TO_PACKET, not PTR_TO_MEM, because
these pointers need to be invalidated on clear_all_pkt_pointers invocation, and
it is also more meaningful to the user to see return value as R0=pkt.
This series is meant to collect feedback on the approach, next version can
include a bpf_skb_pointer and exposing it as bpf_packet_pointer helper for TC
hooks, and explore not resetting range to zero on r0 += rX, instead check access
like check_mem_region_access (var_off + off < range), since there would be no
data_end to compare against and obtain a new range.
The common name and func_id is supposed to allow writing generic code using
bpf_packet_pointer that works for both XDP and TC programs.
Please see the individual patches for implementation details.
Kumar Kartikeya Dwivedi (5):
bpf: Add ARG_SCALAR and ARG_CONSTANT
bpf: Introduce pkt_uid concept for PTR_TO_PACKET
bpf: Introduce bpf_packet_pointer helper to do DPA
selftests/bpf: Add verifier tests for pkt pointer with pkt_uid
selftests/bpf: Update xdp_adjust_frags to use bpf_packet_pointer
include/linux/bpf.h | 4 +
include/linux/bpf_verifier.h | 9 +-
include/uapi/linux/bpf.h | 12 ++
kernel/bpf/verifier.c | 97 ++++++++++--
net/core/filter.c | 48 +++---
tools/include/uapi/linux/bpf.h | 12 ++
.../bpf/prog_tests/xdp_adjust_frags.c | 46 ++++--
.../bpf/progs/test_xdp_update_frags.c | 46 ++++--
tools/testing/selftests/bpf/verifier/xdp.c | 146 ++++++++++++++++++
9 files changed, 358 insertions(+), 62 deletions(-)
--
2.35.1
