clj-ebpf.net.checksum — org.clojars.pgdad/clj-ebpf 0.6.7

Checksum calculation helpers for eBPF programs.

These helpers use BPF kernel helper functions for efficient checksum updates. Most are designed for TC/SKB programs.

BPF-F-MARK-ENFORCE clj

BPF-F-MARK-MANGLED-0 clj

BPF-F-PSEUDO-HDR clj

BPF-F-RECOMPUTE-CSUM clj

BPF-FUNC-csum-diff clj

BPF-FUNC-csum-update clj

BPF-FUNC-l3-csum-replace clj

BPF-FUNC-l4-csum-replace clj

build-csum-diff clj

(build-csum-diff old-ptr-reg old-size new-ptr-reg new-size seed)

Generate bpf_csum_diff call for computing checksum difference.

Lower-level helper for complex checksum updates (e.g., when replacing multiple fields or entire headers).

Args: old-ptr-reg: Register with pointer to old data (or 0) old-size: Size of old data (or 0) new-ptr-reg: Register with pointer to new data (or 0) new-size: Size of new data (or 0) seed: Initial checksum value (0 for new calculation)

Returns: Vector of instructions, result in r0 (checksum delta)

build-l3-csum-replace clj

Alias for l3-csum-replace-4. Generate incremental IP header checksum update.

Used when modifying IP header fields (e.g., TTL, addresses for NAT).

Args: ctx-reg: Register containing skb pointer csum-off: Byte offset of checksum field in packet old-reg: Register containing old value new-reg: Register containing new value

Returns: Vector of instructions, result in r0 (0 on success)

build-l4-csum-replace clj

(build-l4-csum-replace ctx-reg csum-off old-reg new-reg flags)

Generate incremental L4 (TCP/UDP) checksum update.

Used when modifying IP addresses or L4 ports. For IP address changes, use BPF-F-PSEUDO-HDR flag to account for pseudo-header.

Args: ctx-reg: Register containing skb pointer csum-off: Byte offset of L4 checksum field in packet old-reg: Register containing old value new-reg: Register containing new value flags: BPF_F flags: - 0: Simple value replacement - BPF-F-PSEUDO-HDR (0x10): Account for IP pseudo-header - BPF-F-RECOMPUTE-CSUM (0x01): Recompute full checksum

Returns: Vector of instructions

csum-diff clj

(csum-diff from-ptr-reg from-size to-ptr-reg to-size seed-reg)

Generate instructions to compute checksum difference. Uses bpf_csum_diff kernel helper.

Works in both XDP and TC programs.

from-ptr-reg: Pointer to old data (can be stack or map value) from-size: Size of old data in bytes (must be multiple of 4) to-ptr-reg: Pointer to new data to-size: Size of new data in bytes (must be multiple of 4) seed-reg: Initial checksum value (0 for new calculation)

Returns: Checksum difference in r0

Clobbers: r1-r5, r0

fold-csum-32 clj

(fold-csum-32 csum-reg scratch-reg)

Fold a 32-bit checksum value into 16 bits. Used after accumulating checksum values.

csum-reg: Register containing 32-bit checksum (will be modified to 16-bit)

l3-csum-replace-2 clj

(l3-csum-replace-2 skb-reg csum-offset old-val-reg new-val-reg)

Generate instructions to update L3 checksum for a 2-byte value change.

skb-reg: SKB pointer register csum-offset: Offset to checksum field from packet start old-val-reg: Register with old 2-byte value new-val-reg: Register with new 2-byte value

Clobbers: r1-r5, r0

l3-csum-replace-4 clj

(l3-csum-replace-4 skb-reg csum-offset old-val-reg new-val-reg)

Generate instructions to update L3 (IP) checksum for a 4-byte value change. Uses bpf_l3_csum_replace kernel helper.

For TC programs only (requires SKB).

skb-reg: SKB pointer register (typically :r1 saved to callee-saved reg) csum-offset: Offset to checksum field from packet start old-val-reg: Register with old 4-byte value new-val-reg: Register with new 4-byte value

Clobbers: r1-r5, r0 (return value)

l4-csum-replace-2 clj

(l4-csum-replace-2 skb-reg csum-offset old-val-reg new-val-reg pseudo-hdr?)

Generate instructions to update L4 checksum for a 2-byte value change.

skb-reg: SKB pointer register csum-offset: Offset to checksum field from packet start old-val-reg: Register with old 2-byte value new-val-reg: Register with new 2-byte value pseudo-hdr?: If true, include BPF_F_PSEUDO_HDR flag

Clobbers: r1-r5, r0

l4-csum-replace-4 clj

(l4-csum-replace-4 skb-reg csum-offset old-val-reg new-val-reg pseudo-hdr?)

Generate instructions to update L4 (TCP/UDP) checksum for a 4-byte value change. Uses bpf_l4_csum_replace kernel helper.

For TC programs only (requires SKB).

skb-reg: SKB pointer register csum-offset: Offset to checksum field from packet start old-val-reg: Register with old 4-byte value new-val-reg: Register with new 4-byte value pseudo-hdr?: If true, include BPF_F_PSEUDO_HDR flag (for IP address changes)

Clobbers: r1-r5, r0

negate-csum clj

(negate-csum csum-reg)

Negate checksum (one's complement).

csum-reg: Register containing checksum (will be negated)

update-ip-checksum clj

(update-ip-checksum skb-reg ip-hdr-offset old-val-reg new-val-reg)

Update IP checksum after changing a 4-byte field (e.g., saddr or daddr).

skb-reg: SKB pointer register ip-hdr-offset: Offset to IP header from packet start (typically 14) old-val-reg: Register with old value new-val-reg: Register with new value

Clobbers: r1-r5, r0

update-tcp-checksum-for-ip clj

(update-tcp-checksum-for-ip skb-reg l4-hdr-offset old-ip-reg new-ip-reg)

Update TCP checksum after IP address change. TCP checksum includes pseudo-header with IP addresses.

skb-reg: SKB pointer register l4-hdr-offset: Offset to TCP header from packet start old-ip-reg: Register with old IP address new-ip-reg: Register with new IP address

Clobbers: r1-r5, r0

update-tcp-checksum-for-port clj

(update-tcp-checksum-for-port skb-reg l4-hdr-offset old-port-reg new-port-reg)

Update TCP checksum after port change.

skb-reg: SKB pointer register l4-hdr-offset: Offset to TCP header from packet start old-port-reg: Register with old port (network order) new-port-reg: Register with new port (network order)

Clobbers: r1-r5, r0

update-udp-checksum-for-ip clj

(update-udp-checksum-for-ip skb-reg l4-hdr-offset old-ip-reg new-ip-reg)

Update UDP checksum after IP address change. UDP checksum includes pseudo-header with IP addresses.

skb-reg: SKB pointer register l4-hdr-offset: Offset to UDP header from packet start old-ip-reg: Register with old IP address new-ip-reg: Register with new IP address

Clobbers: r1-r5, r0

update-udp-checksum-for-port clj

(update-udp-checksum-for-port skb-reg l4-hdr-offset old-port-reg new-port-reg)

Update UDP checksum after port change.

skb-reg: SKB pointer register l4-hdr-offset: Offset to UDP header from packet start old-port-reg: Register with old port (network order) new-port-reg: Register with new port (network order)

Clobbers: r1-r5, r0