bpf_load.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <libelf.h>
#include <gelf.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <stdbool.h>
#include <stdlib.h>
#include <linux/bpf.h>
#include <linux/filter.h>
#include <linux/perf_event.h>
#include <sys/syscall.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <poll.h>
#include <ctype.h>
#include "libbpf.h"
#include "bpf_helpers.h"
#include "bpf_load.h"

#define DEBUGFS "/sys/kernel/debug/tracing/"

static char license[128];
static int kern_version;
static bool processed_sec[128];
int map_fd[MAX_MAPS];
int prog_fd[MAX_PROGS];
int event_fd[MAX_PROGS];
int prog_cnt;
int prog_array_fd = -1;

static int populate_prog_array(const char *event, int prog_fd)
{
    int ind = atoi(event), err;

    err = bpf_update_elem(prog_array_fd, &ind, &prog_fd, BPF_ANY);
    if (err < 0) {
        printf("failed to store prog_fd in prog_array\n");
        return -1;
    }
    return 0;
}

static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
{
    bool is_socket = strncmp(event, "socket", 6) == 0;
    bool is_kprobe = strncmp(event, "kprobe/", 7) == 0;
    bool is_kretprobe = strncmp(event, "kretprobe/", 10) == 0;
    bool is_tracepoint = strncmp(event, "tracepoint/", 11) == 0;
    bool is_xdp = strncmp(event, "xdp", 3) == 0;
    bool is_perf_event = strncmp(event, "perf_event", 10) == 0;
    enum bpf_prog_type prog_type;
    char buf[256];
    int fd, efd, err, id;
    struct perf_event_attr attr = {};

    attr.type = PERF_TYPE_TRACEPOINT;
    attr.sample_type = PERF_SAMPLE_RAW;
    attr.sample_period = 1;
    attr.wakeup_events = 1;

    if (is_socket) {
        prog_type = BPF_PROG_TYPE_SOCKET_FILTER;
    } else if (is_kprobe || is_kretprobe) {
        prog_type = BPF_PROG_TYPE_KPROBE;
    } else if (is_tracepoint) {
        prog_type = BPF_PROG_TYPE_TRACEPOINT;
    } else if (is_xdp) {
        prog_type = BPF_PROG_TYPE_XDP;
    } else if (is_perf_event) {
        prog_type = BPF_PROG_TYPE_PERF_EVENT;
    } else {
        printf("Unknown event '%s'\n", event);
        return -1;
    }

    fd = bpf_prog_load(prog_type, prog, size, license, kern_version);
    if (fd < 0) {
        printf("bpf_prog_load() err=%d\n%s", errno, bpf_log_buf);
        return -1;
    }

    prog_fd[prog_cnt++] = fd;

    if (is_xdp || is_perf_event)
        return 0;

    if (is_socket) {
        event += 6;
        if (*event != '/')
            return 0;
        event++;
        if (!isdigit(*event)) {
            printf("invalid prog number\n");
            return -1;
        }
        return populate_prog_array(event, fd);
    }

    if (is_kprobe || is_kretprobe) {
        if (is_kprobe)
            event += 7;
        else
            event += 10;

        if (*event == 0) {
            printf("event name cannot be empty\n");
            return -1;
        }

        if (isdigit(*event))
            return populate_prog_array(event, fd);

        snprintf(buf, sizeof(buf),
             "echo '%c:%s %s' >> /sys/kernel/debug/tracing/kprobe_events",
             is_kprobe ? 'p' : 'r', event, event);
        err = system(buf);
        if (err < 0) {
            printf("failed to create kprobe '%s' error '%s'\n",
                   event, strerror(errno));
            return -1;
        }

        strcpy(buf, DEBUGFS);
        strcat(buf, "events/kprobes/");
        strcat(buf, event);
        strcat(buf, "/id");
    } else if (is_tracepoint) {
        event += 11;

        if (*event == 0) {
            printf("event name cannot be empty\n");
            return -1;
        }
        strcpy(buf, DEBUGFS);
        strcat(buf, "events/");
        strcat(buf, event);
        strcat(buf, "/id");
    }

    efd = open(buf, O_RDONLY, 0);
    if (efd < 0) {
        printf("failed to open event %s\n", event);
        return -1;
    }

    err = read(efd, buf, sizeof(buf));
    if (err < 0 || err >= sizeof(buf)) {
        printf("read from '%s' failed '%s'\n", event, strerror(errno));
        return -1;
    }

    close(efd);

    buf[err] = 0;
    id = atoi(buf);
    attr.config = id;

    efd = perf_event_open(&attr, -1/*pid*/, 0/*cpu*/, -1/*group_fd*/, 0);
    if (efd < 0) {
        printf("event %d fd %d err %s\n", id, efd, strerror(errno));
        return -1;
    }
    event_fd[prog_cnt - 1] = efd;
    ioctl(efd, PERF_EVENT_IOC_ENABLE, 0);
    ioctl(efd, PERF_EVENT_IOC_SET_BPF, fd);

    return 0;
}

static int load_maps(struct bpf_map_def *maps, int len)
{
    int i;

    for (i = 0; i < len / sizeof(struct bpf_map_def); i++) {

        map_fd[i] = bpf_create_map(maps[i].type,
                       maps[i].key_size,
                       maps[i].value_size,
                       maps[i].max_entries,
                       maps[i].map_flags);
        if (map_fd[i] < 0) {
            printf("failed to create a map: %d %s\n",
                   errno, strerror(errno));
            return 1;
        }

        if (maps[i].type == BPF_MAP_TYPE_PROG_ARRAY)
            prog_array_fd = map_fd[i];
        printf("New map %d: k %d v %d e %d f %d\n", i, maps[i].key_size, maps[i].value_size, maps[i].max_entries, maps[i].map_flags);
    }
    return 0;
}

static int get_sec(Elf *elf, int i, GElf_Ehdr *ehdr, char **shname,
           GElf_Shdr *shdr, Elf_Data **data)
{
    Elf_Scn *scn;

    scn = elf_getscn(elf, i);
    if (!scn)
        return 1;

    if (gelf_getshdr(scn, shdr) != shdr)
        return 2;

    *shname = elf_strptr(elf, ehdr->e_shstrndx, shdr->sh_name);
    if (!*shname || !shdr->sh_size)
        return 3;

    *data = elf_getdata(scn, 0);
    if (!*data || elf_getdata(scn, *data) != NULL)
        return 4;

    return 0;
}

static int parse_relo_and_apply(Elf_Data *data, Elf_Data *symbols,
                GElf_Shdr *shdr, struct bpf_insn *insn)
{
    int i, nrels;

    nrels = shdr->sh_size / shdr->sh_entsize;

    for (i = 0; i < nrels; i++) {
        GElf_Sym sym;
        GElf_Rel rel;
        unsigned int insn_idx;

        gelf_getrel(data, i, &rel);

        insn_idx = rel.r_offset / sizeof(struct bpf_insn);

        gelf_getsym(symbols, GELF_R_SYM(rel.r_info), &sym);

        if (insn[insn_idx].code != (BPF_LD | BPF_IMM | BPF_DW)) {
            printf("invalid relo for insn[%d].code 0x%x\n",
                   insn_idx, insn[insn_idx].code);
            return 1;
        }
        insn[insn_idx].src_reg = BPF_PSEUDO_MAP_FD;
        insn[insn_idx].imm = map_fd[sym.st_value / sizeof(struct bpf_map_def)];
    }

    return 0;
}

int load_bpf_file(char *path)
{
    int fd, i;
    Elf *elf;
    GElf_Ehdr ehdr;
    GElf_Shdr shdr, shdr_prog;
    Elf_Data *data, *data_prog, *symbols = NULL;
    char *shname, *shname_prog;

    if (elf_version(EV_CURRENT) == EV_NONE)
        return 1;

    fd = open(path, O_RDONLY, 0);
    if (fd < 0)
        return 1;

    elf = elf_begin(fd, ELF_C_READ, NULL);

    if (!elf)
        return 1;

    if (gelf_getehdr(elf, &ehdr) != &ehdr)
        return 1;

    /* clear all kprobes */
    i = system("echo \"\" > /sys/kernel/debug/tracing/kprobe_events");

    /* scan over all elf sections to get license and map info */
    for (i = 1; i < ehdr.e_shnum; i++) {

        if (get_sec(elf, i, &ehdr, &shname, &shdr, &data))
            continue;

        if (1) /* helpful for llvm debugging */
            printf("section %d:%s data %p size %zd link %d flags %d\n",
                   i, shname, data->d_buf, data->d_size,
                   shdr.sh_link, (int) shdr.sh_flags);

        if (strcmp(shname, "license") == 0) {
            processed_sec[i] = true;
            memcpy(license, data->d_buf, data->d_size);
        } else if (strcmp(shname, "version") == 0) {
            processed_sec[i] = true;
            if (data->d_size != sizeof(int)) {
                printf("invalid size of version section %zd\n",
                       data->d_size);
                return 1;
            }
            memcpy(&kern_version, data->d_buf, sizeof(int));
        } else if (strcmp(shname, "maps") == 0) {
            processed_sec[i] = true;
            if (load_maps(data->d_buf, data->d_size))
                return 1;
        } else if (shdr.sh_type == SHT_SYMTAB) {
            symbols = data;
        }
    }

    /* load programs that need map fixup (relocations) */
    for (i = 1; i < ehdr.e_shnum; i++) {

        if (get_sec(elf, i, &ehdr, &shname, &shdr, &data))
            continue;
        if (shdr.sh_type == SHT_REL) {
            struct bpf_insn *insns;

            if (get_sec(elf, shdr.sh_info, &ehdr, &shname_prog,
                    &shdr_prog, &data_prog))
                continue;

            insns = (struct bpf_insn *) data_prog->d_buf;

            processed_sec[shdr.sh_info] = true;
            processed_sec[i] = true;

            if (parse_relo_and_apply(data, symbols, &shdr, insns)) {
                printf("reloc %s\n", shname_prog);
                continue;
            }

            if (memcmp(shname_prog, "kprobe/", 7) == 0 ||
                memcmp(shname_prog, "kretprobe/", 10) == 0 ||
                memcmp(shname_prog, "tracepoint/", 11) == 0 ||
                memcmp(shname_prog, "xdp", 3) == 0 ||
                memcmp(shname_prog, "perf_event", 10) == 0 ||
                memcmp(shname_prog, "socket", 6) == 0)
                load_and_attach(shname_prog, insns, data_prog->d_size);
        }
    }

    /* load programs that don't use maps */
    for (i = 1; i < ehdr.e_shnum; i++) {

        if (processed_sec[i])
            continue;

        if (get_sec(elf, i, &ehdr, &shname, &shdr, &data))
            continue;

        if (memcmp(shname, "kprobe/", 7) == 0 ||
            memcmp(shname, "kretprobe/", 10) == 0 ||
            memcmp(shname, "tracepoint/", 11) == 0 ||
            memcmp(shname, "xdp", 3) == 0 ||
            memcmp(shname, "perf_event", 10) == 0 ||
            memcmp(shname, "socket", 6) == 0)
            load_and_attach(shname, data->d_buf, data->d_size);
    }

    close(fd);
    return 0;
}

void read_trace_pipe(void)
{
    int trace_fd;

    trace_fd = open(DEBUGFS "trace_pipe", O_RDONLY, 0);
    if (trace_fd < 0)
        return;

    while (1) {
        static char buf[4096];
        ssize_t sz;

        sz = read(trace_fd, buf, sizeof(buf));
        if (sz > 0) {
            buf[sz] = 0;
            puts(buf);
        }
    }
}

#define MAX_SYMS 300000
static struct ksym syms[MAX_SYMS];
static int sym_cnt;

static int ksym_cmp(const void *p1, const void *p2)
{
    return ((struct ksym *)p1)->addr - ((struct ksym *)p2)->addr;
}

int load_kallsyms(void)
{
    FILE *f = fopen("/proc/kallsyms", "r");
    char func[256], buf[256];
    char symbol;
    void *addr;
    int i = 0;

    if (!f)
        return -ENOENT;

    while (!feof(f)) {
        if (!fgets(buf, sizeof(buf), f))
            break;
        if (sscanf(buf, "%p %c %s", &addr, &symbol, func) != 3)
            break;
        if (!addr)
            continue;
        syms[i].addr = (long) addr;
        syms[i].name = strdup(func);
        i++;
    }
    sym_cnt = i;
    qsort(syms, sym_cnt, sizeof(struct ksym), ksym_cmp);
    return 0;
}

struct ksym *ksym_search(long key)
{
    int start = 0, end = sym_cnt;
    int result;

    while (start < end) {
        size_t mid = start + (end - start) / 2;

        result = key - syms[mid].addr;
        if (result < 0)
            end = mid;
        else if (result > 0)
            start = mid + 1;
        else
            return &syms[mid];
    }

    if (start >= 1 && syms[start - 1].addr < key &&
        key < syms[start].addr)
        /* valid ksym */
        return &syms[start - 1];

    /* out of range. return _stext */
    return &syms[0];
}