bpf_helpers.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __BPF_HELPERS_H
#define __BPF_HELPERS_H

/* helper macro to place programs, maps, license in
 * different sections in elf_bpf file. Section names
 * are interpreted by elf_bpf loader
 */
#define SEC(NAME) __attribute__((section(NAME), used))

/* helper functions called from eBPF programs written in C */
static void *(*bpf_map_lookup_elem)(void *map, void *key) =
        (void *) BPF_FUNC_map_lookup_elem;
static int (*bpf_map_update_elem)(void *map, void *key, void *value,
                                  unsigned long long flags) =
        (void *) BPF_FUNC_map_update_elem;
static int (*bpf_map_delete_elem)(void *map, void *key) =
        (void *) BPF_FUNC_map_delete_elem;
static int (*bpf_probe_read)(void *dst, int size, void *unsafe_ptr) =
        (void *) BPF_FUNC_probe_read;
static unsigned long long (*bpf_ktime_get_ns)(void) =
        (void *) BPF_FUNC_ktime_get_ns;
static int (*bpf_trace_printk)(const char *fmt, int fmt_size, ...) =
        (void *) BPF_FUNC_trace_printk;
static void (*bpf_tail_call)(void *ctx, void *map, int index) =
        (void *) BPF_FUNC_tail_call;
static unsigned long long (*bpf_get_smp_processor_id)(void) =
        (void *) BPF_FUNC_get_smp_processor_id;
static unsigned long long (*bpf_get_current_pid_tgid)(void) =
        (void *) BPF_FUNC_get_current_pid_tgid;
static unsigned long long (*bpf_get_current_uid_gid)(void) =
        (void *) BPF_FUNC_get_current_uid_gid;
static int (*bpf_get_current_comm)(void *buf, int buf_size) =
        (void *) BPF_FUNC_get_current_comm;
static unsigned long long (*bpf_perf_event_read)(void *map,
                                                 unsigned long long flags) =
        (void *) BPF_FUNC_perf_event_read;
static int (*bpf_clone_redirect)(void *ctx, int ifindex, int flags) =
        (void *) BPF_FUNC_clone_redirect;
static int (*bpf_redirect)(int ifindex, int flags) =
        (void *) BPF_FUNC_redirect;
// static int (*bpf_redirect_map)(void *map, int key, int flags) =
//      (void *) BPF_FUNC_redirect_map;
static int (*bpf_perf_event_output)(void *ctx, void *map,
                                    unsigned long long flags, void *data,
                                    int size) =
        (void *) BPF_FUNC_perf_event_output;
static int (*bpf_get_stackid)(void *ctx, void *map, int flags) =
        (void *) BPF_FUNC_get_stackid;
static int (*bpf_probe_write_user)(void *dst, void *src, int size) =
        (void *) BPF_FUNC_probe_write_user;
static int (*bpf_current_task_under_cgroup)(void *map, int index) =
        (void *) BPF_FUNC_current_task_under_cgroup;
static int (*bpf_skb_get_tunnel_key)(void *ctx, void *key, int size, int flags) =
        (void *) BPF_FUNC_skb_get_tunnel_key;
static int (*bpf_skb_set_tunnel_key)(void *ctx, void *key, int size, int flags) =
        (void *) BPF_FUNC_skb_set_tunnel_key;
static int (*bpf_skb_get_tunnel_opt)(void *ctx, void *md, int size) =
        (void *) BPF_FUNC_skb_get_tunnel_opt;
static int (*bpf_skb_set_tunnel_opt)(void *ctx, void *md, int size) =
        (void *) BPF_FUNC_skb_set_tunnel_opt;
static unsigned long long (*bpf_get_prandom_u32)(void) =
        (void *) BPF_FUNC_get_prandom_u32;
// static int (*bpf_xdp_adjust_head)(void *ctx, int offset) =
//      (void *) BPF_FUNC_xdp_adjust_head;
// static int (*bpf_xdp_adjust_meta)(void *ctx, int offset) =
//      (void *) BPF_FUNC_xdp_adjust_meta;
// static int (*bpf_setsockopt)(void *ctx, int level, int optname, void *optval,
//                           int optlen) =
//      (void *) BPF_FUNC_setsockopt;
// static int (*bpf_getsockopt)(void *ctx, int level, int optname, void *optval,
//                           int optlen) =
//      (void *) BPF_FUNC_getsockopt;
// static int (*bpf_sock_ops_cb_flags_set)(void *ctx, int flags) =
//      (void *) BPF_FUNC_sock_ops_cb_flags_set;
// static int (*bpf_sk_redirect_map)(void *ctx, void *map, int key, int flags) =
//      (void *) BPF_FUNC_sk_redirect_map;
// static int (*bpf_sk_redirect_hash)(void *ctx, void *map, void *key, int flags) =
//      (void *) BPF_FUNC_sk_redirect_hash;
// static int (*bpf_sock_map_update)(void *map, void *key, void *value,
//                                unsigned long long flags) =
//      (void *) BPF_FUNC_sock_map_update;
// static int (*bpf_sock_hash_update)(void *map, void *key, void *value,
//                                 unsigned long long flags) =
//      (void *) BPF_FUNC_sock_hash_update;
// static int (*bpf_perf_event_read_value)(void *map, unsigned long long flags,
//                                      void *buf, unsigned int buf_size) =
//      (void *) BPF_FUNC_perf_event_read_value;
// static int (*bpf_perf_prog_read_value)(void *ctx, void *buf,
//                                     unsigned int buf_size) =
//      (void *) BPF_FUNC_perf_prog_read_value;
// static int (*bpf_override_return)(void *ctx, unsigned long rc) =
//      (void *) BPF_FUNC_override_return;
// static int (*bpf_msg_redirect_map)(void *ctx, void *map, int key, int flags) =
//      (void *) BPF_FUNC_msg_redirect_map;
// static int (*bpf_msg_redirect_hash)(void *ctx,
//                                  void *map, void *key, int flags) =
//      (void *) BPF_FUNC_msg_redirect_hash;
// static int (*bpf_msg_apply_bytes)(void *ctx, int len) =
//      (void *) BPF_FUNC_msg_apply_bytes;
// static int (*bpf_msg_cork_bytes)(void *ctx, int len) =
//      (void *) BPF_FUNC_msg_cork_bytes;
// static int (*bpf_msg_pull_data)(void *ctx, int start, int end, int flags) =
//      (void *) BPF_FUNC_msg_pull_data;
// static int (*bpf_bind)(void *ctx, void *addr, int addr_len) =
//      (void *) BPF_FUNC_bind;
// static int (*bpf_xdp_adjust_tail)(void *ctx, int offset) =
//      (void *) BPF_FUNC_xdp_adjust_tail;
// static int (*bpf_skb_get_xfrm_state)(void *ctx, int index, void *state,
//                                   int size, int flags) =
//      (void *) BPF_FUNC_skb_get_xfrm_state;
// static int (*bpf_get_stack)(void *ctx, void *buf, int size, int flags) =
//      (void *) BPF_FUNC_get_stack;
// static int (*bpf_fib_lookup)(void *ctx, struct bpf_fib_lookup *params,
//                           int plen, __u32 flags) =
//      (void *) BPF_FUNC_fib_lookup;
// static int (*bpf_lwt_push_encap)(void *ctx, unsigned int type, void *hdr,
//                               unsigned int len) =
//      (void *) BPF_FUNC_lwt_push_encap;
// static int (*bpf_lwt_seg6_store_bytes)(void *ctx, unsigned int offset,
//                                     void *from, unsigned int len) =
//      (void *) BPF_FUNC_lwt_seg6_store_bytes;
// static int (*bpf_lwt_seg6_action)(void *ctx, unsigned int action, void *param,
//                                unsigned int param_len) =
//      (void *) BPF_FUNC_lwt_seg6_action;
// static int (*bpf_lwt_seg6_adjust_srh)(void *ctx, unsigned int offset,
//                                    unsigned int len) =
//      (void *) BPF_FUNC_lwt_seg6_adjust_srh;
// static int (*bpf_rc_repeat)(void *ctx) =
//      (void *) BPF_FUNC_rc_repeat;
// static int (*bpf_rc_keydown)(void *ctx, unsigned int protocol,
//                           unsigned long long scancode, unsigned int toggle) =
//      (void *) BPF_FUNC_rc_keydown;
// static unsigned long long (*bpf_get_current_cgroup_id)(void) =
//      (void *) BPF_FUNC_get_current_cgroup_id;

/* llvm builtin functions that eBPF C program may use to
 * emit BPF_LD_ABS and BPF_LD_IND instructions
 */
struct sk_buff;
unsigned long long load_byte(void *skb,
                             unsigned long long off) asm("llvm.bpf.load.byte");
unsigned long long load_half(void *skb,
                             unsigned long long off) asm("llvm.bpf.load.half");
unsigned long long load_word(void *skb,
                             unsigned long long off) asm("llvm.bpf.load.word");

/* a helper structure used by eBPF C program
 * to describe map attributes to elf_bpf loader
 */
struct bpf_map_def {
        unsigned int type;
        unsigned int key_size;
        unsigned int value_size;
        unsigned int max_entries;
        unsigned int map_flags;
        unsigned int inner_map_idx;
        unsigned int numa_node;
};

#define BPF_ANNOTATE_KV_PAIR(name, type_key, type_val)          \
        struct ____btf_map_##name {                             \
                type_key key;                                   \
                type_val value;                                 \
        };                                                      \
        struct ____btf_map_##name                               \
        __attribute__ ((section(".maps." #name), used))         \
                ____btf_map_##name = { }

static int (*bpf_skb_load_bytes)(void *ctx, int off, void *to, int len) =
        (void *) BPF_FUNC_skb_load_bytes;
static int (*bpf_skb_store_bytes)(void *ctx, int off, void *from, int len, int flags) =
        (void *) BPF_FUNC_skb_store_bytes;
static int (*bpf_l3_csum_replace)(void *ctx, int off, int from, int to, int flags) =
        (void *) BPF_FUNC_l3_csum_replace;
static int (*bpf_l4_csum_replace)(void *ctx, int off, int from, int to, int flags) =
        (void *) BPF_FUNC_l4_csum_replace;
static int (*bpf_csum_diff)(void *from, int from_size, void *to, int to_size, int seed) =
        (void *) BPF_FUNC_csum_diff;
static int (*bpf_skb_under_cgroup)(void *ctx, void *map, int index) =
        (void *) BPF_FUNC_skb_under_cgroup;
// static int (*bpf_skb_change_head)(void *, int len, int flags) =
//      (void *) BPF_FUNC_skb_change_head;
static int (*bpf_skb_pull_data)(void *, int len) =
        (void *) BPF_FUNC_skb_pull_data;

/* Scan the ARCH passed in from ARCH env variable (see Makefile) */
#if defined(__TARGET_ARCH_x86)
        #define bpf_target_x86
        #define bpf_target_defined
#elif defined(__TARGET_ARCH_s930x)
        #define bpf_target_s930x
        #define bpf_target_defined
#elif defined(__TARGET_ARCH_arm64)
        #define bpf_target_arm64
        #define bpf_target_defined
#elif defined(__TARGET_ARCH_mips)
        #define bpf_target_mips
        #define bpf_target_defined
#elif defined(__TARGET_ARCH_powerpc)
        #define bpf_target_powerpc
        #define bpf_target_defined
#elif defined(__TARGET_ARCH_sparc)
        #define bpf_target_sparc
        #define bpf_target_defined
#else
        #undef bpf_target_defined
#endif

/* Fall back to what the compiler says */
#ifndef bpf_target_defined
#if defined(__x86_64__)
        #define bpf_target_x86
#elif defined(__s390x__)
        #define bpf_target_s930x
#elif defined(__aarch64__)
        #define bpf_target_arm64
#elif defined(__mips__)
        #define bpf_target_mips
#elif defined(__powerpc__)
        #define bpf_target_powerpc
#elif defined(__sparc__)
        #define bpf_target_sparc
#endif
#endif

#if defined(bpf_target_x86)

#define PT_REGS_PARM1(x) ((x)->di)
#define PT_REGS_PARM2(x) ((x)->si)
#define PT_REGS_PARM3(x) ((x)->dx)
#define PT_REGS_PARM4(x) ((x)->cx)
#define PT_REGS_PARM5(x) ((x)->r8)
#define PT_REGS_RET(x) ((x)->sp)
#define PT_REGS_FP(x) ((x)->bp)
#define PT_REGS_RC(x) ((x)->ax)
#define PT_REGS_SP(x) ((x)->sp)
#define PT_REGS_IP(x) ((x)->ip)

#elif defined(bpf_target_s390x)

#define PT_REGS_PARM1(x) ((x)->gprs[2])
#define PT_REGS_PARM2(x) ((x)->gprs[3])
#define PT_REGS_PARM3(x) ((x)->gprs[4])
#define PT_REGS_PARM4(x) ((x)->gprs[5])
#define PT_REGS_PARM5(x) ((x)->gprs[6])
#define PT_REGS_RET(x) ((x)->gprs[14])
#define PT_REGS_FP(x) ((x)->gprs[11]) /* Works only with CONFIG_FRAME_POINTER */
#define PT_REGS_RC(x) ((x)->gprs[2])
#define PT_REGS_SP(x) ((x)->gprs[15])
#define PT_REGS_IP(x) ((x)->psw.addr)

#elif defined(bpf_target_arm64)

#define PT_REGS_PARM1(x) ((x)->regs[0])
#define PT_REGS_PARM2(x) ((x)->regs[1])
#define PT_REGS_PARM3(x) ((x)->regs[2])
#define PT_REGS_PARM4(x) ((x)->regs[3])
#define PT_REGS_PARM5(x) ((x)->regs[4])
#define PT_REGS_RET(x) ((x)->regs[30])
#define PT_REGS_FP(x) ((x)->regs[29]) /* Works only with CONFIG_FRAME_POINTER */
#define PT_REGS_RC(x) ((x)->regs[0])
#define PT_REGS_SP(x) ((x)->sp)
#define PT_REGS_IP(x) ((x)->pc)

#elif defined(bpf_target_mips)

#define PT_REGS_PARM1(x) ((x)->regs[4])
#define PT_REGS_PARM2(x) ((x)->regs[5])
#define PT_REGS_PARM3(x) ((x)->regs[6])
#define PT_REGS_PARM4(x) ((x)->regs[7])
#define PT_REGS_PARM5(x) ((x)->regs[8])
#define PT_REGS_RET(x) ((x)->regs[31])
#define PT_REGS_FP(x) ((x)->regs[30]) /* Works only with CONFIG_FRAME_POINTER */
#define PT_REGS_RC(x) ((x)->regs[1])
#define PT_REGS_SP(x) ((x)->regs[29])
#define PT_REGS_IP(x) ((x)->cp0_epc)

#elif defined(bpf_target_powerpc)

#define PT_REGS_PARM1(x) ((x)->gpr[3])
#define PT_REGS_PARM2(x) ((x)->gpr[4])
#define PT_REGS_PARM3(x) ((x)->gpr[5])
#define PT_REGS_PARM4(x) ((x)->gpr[6])
#define PT_REGS_PARM5(x) ((x)->gpr[7])
#define PT_REGS_RC(x) ((x)->gpr[3])
#define PT_REGS_SP(x) ((x)->sp)
#define PT_REGS_IP(x) ((x)->nip)

#elif defined(bpf_target_sparc)

#define PT_REGS_PARM1(x) ((x)->u_regs[UREG_I0])
#define PT_REGS_PARM2(x) ((x)->u_regs[UREG_I1])
#define PT_REGS_PARM3(x) ((x)->u_regs[UREG_I2])
#define PT_REGS_PARM4(x) ((x)->u_regs[UREG_I3])
#define PT_REGS_PARM5(x) ((x)->u_regs[UREG_I4])
#define PT_REGS_RET(x) ((x)->u_regs[UREG_I7])
#define PT_REGS_RC(x) ((x)->u_regs[UREG_I0])
#define PT_REGS_SP(x) ((x)->u_regs[UREG_FP])

/* Should this also be a bpf_target check for the sparc case? */
#if defined(__arch64__)
#define PT_REGS_IP(x) ((x)->tpc)
#else
#define PT_REGS_IP(x) ((x)->pc)
#endif

#endif

#ifdef bpf_target_powerpc
#define BPF_KPROBE_READ_RET_IP(ip, ctx)         ({ (ip) = (ctx)->link; })
#define BPF_KRETPROBE_READ_RET_IP               BPF_KPROBE_READ_RET_IP
#elif bpf_target_sparc
#define BPF_KPROBE_READ_RET_IP(ip, ctx)         ({ (ip) = PT_REGS_RET(ctx); })
#define BPF_KRETPROBE_READ_RET_IP               BPF_KPROBE_READ_RET_IP
#else
#define BPF_KPROBE_READ_RET_IP(ip, ctx)         ({                              \
                bpf_probe_read(&(ip), sizeof(ip), (void *)PT_REGS_RET(ctx)); })
#define BPF_KRETPROBE_READ_RET_IP(ip, ctx)      ({                              \
                bpf_probe_read(&(ip), sizeof(ip),                               \
                                (void *)(PT_REGS_FP(ctx) + sizeof(ip))); })
#endif

#endif

ebpf_esp_proto.c

//clang -O2 -target bpf -c ebpf_esp_proto.c -o ebpf_esp_proto.o -I/usr/include/x86_64-linux-gnu/
#include <stddef.h>
#include <linux/bpf.h>
#include <linux/in.h>
#include <linux/ipv6.h>

/* https://github.com/torvalds/linux/blob/master/tools/testing/selftests/bpf/bpf_helpers.h */
#include "bpf_helpers.h"

SEC("nexthdr")
int do_nexthdr(struct __sk_buff *skb)
{
    __u8 src=50, dst=53;
    struct ipv6hdr *ip6h  = (void *)(long)skb->data;

    if (skb->data + sizeof(struct ipv6hdr) > skb->data_end)
        return 0; //BPF_OK;

    if (ip6h->nexthdr == src)
        bpf_skb_store_bytes(skb, offsetof(struct ipv6hdr, nexthdr), &dst, 1, 0);
    else if (ip6h->nexthdr == dst)
        bpf_skb_store_bytes(skb, offsetof(struct ipv6hdr, nexthdr), &src, 1, 0);

    return 0; //BPF_OK;
}

char __license[] SEC("license") = "GPL";