hyp/hypd/server/hyp_bpf.c

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/*
Copyright © 2024 Steven Polley <himself@stevenpolley.net>
*/
//go:build ignore
#include "vmlinux.h"
#include "bpf_endian.h"
#include <bpf/bpf_helpers.h>
char __license[] SEC("license") = "BSD";
// representation of knock data that gets sent to userspace
struct knock_data {
__u32 srcip; // 4 bytes
__u16 dstport; // 2 bytes
__u16 pad; // required padding - struct must be multiple of 4 bytes
};
// ring buffer used to send data to userspace
struct {
__uint(type, BPF_MAP_TYPE_RINGBUF);
__uint(max_entries, 1 << 24);
} rb SEC(".maps");
// force emitting struct event into the ELF
const struct knock_data *unused __attribute__((unused));
// hook into xpress data path attach point
SEC("xdp")
int xdp_prog_func(struct xdp_md *ctx) {
// xdp gives us the raw frame with no structures, it must be parsed
void *data = (void *)(long)ctx->data;
void *data_end = (void *)(long)ctx->data_end;
// A knock should not contain any data
if (data_end - data > 60) {
goto done;
}
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// parse ethernet header
struct ethhdr *eth = data;
if ((void *)eth + sizeof(*eth) <= data_end) {
// parse IP header
struct iphdr *ip = data + sizeof(*eth);
if ((void *)ip + sizeof(*ip) <= data_end) {
if (ip->protocol == IPPROTO_UDP) {
// parse UDP header
struct udphdr *udp = (void *)ip + sizeof(*ip);
if ((void *)udp + sizeof(*udp) <= data_end)
{
// pack into knock structure and send to userspace
struct knock_data knock = {
.srcip = bpf_ntohl(ip->saddr),
.dstport = bpf_htons(udp->dest),
.pad = 0
};
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bpf_ringbuf_output(&rb, &knock, sizeof(knock), BPF_RB_FORCE_WAKEUP);
}
}
}
}
done:
// We send everything to XDP_PASS
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return XDP_PASS;
}