samples: bpf: elf_bpf file loader
simple .o parser and loader using BPF syscall. .o is a standard ELF generated by LLVM backend It parses elf file compiled by llvm .c->.o - parses 'maps' section and creates maps via BPF syscall - parses 'license' section and passes it to syscall - parses elf relocations for BPF maps and adjusts BPF_LD_IMM64 insns by storing map_fd into insn->imm and marking such insns as BPF_PSEUDO_MAP_FD - loads eBPF programs via BPF syscall One ELF file can contain multiple BPF programs. int load_bpf_file(char *path); populates prog_fd[] and map_fd[] with FDs received from bpf syscall bpf_helpers.h - helper functions available to eBPF programs written in C Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>hifive-unleashed-5.1
Alexei Starovoitov
David S. Miller
parent
03f4723ed7
commit
249b812d80
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#ifndef __BPF_HELPERS_H
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#define __BPF_HELPERS_H
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/* helper macro to place programs, maps, license in
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* different sections in elf_bpf file. Section names
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* are interpreted by elf_bpf loader
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*/
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#define SEC(NAME) __attribute__((section(NAME), used))
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/* helper functions called from eBPF programs written in C */
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static void *(*bpf_map_lookup_elem)(void *map, void *key) =
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(void *) BPF_FUNC_map_lookup_elem;
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static int (*bpf_map_update_elem)(void *map, void *key, void *value,
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unsigned long long flags) =
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(void *) BPF_FUNC_map_update_elem;
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static int (*bpf_map_delete_elem)(void *map, void *key) =
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(void *) BPF_FUNC_map_delete_elem;
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/* llvm builtin functions that eBPF C program may use to
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* emit BPF_LD_ABS and BPF_LD_IND instructions
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*/
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struct sk_buff;
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unsigned long long load_byte(void *skb,
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unsigned long long off) asm("llvm.bpf.load.byte");
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unsigned long long load_half(void *skb,
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unsigned long long off) asm("llvm.bpf.load.half");
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unsigned long long load_word(void *skb,
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unsigned long long off) asm("llvm.bpf.load.word");
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/* a helper structure used by eBPF C program
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* to describe map attributes to elf_bpf loader
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*/
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struct bpf_map_def {
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unsigned int type;
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unsigned int key_size;
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unsigned int value_size;
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unsigned int max_entries;
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};
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#endif
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#include <stdio.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <libelf.h>
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#include <gelf.h>
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#include <errno.h>
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#include <unistd.h>
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#include <string.h>
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#include <stdbool.h>
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#include <linux/bpf.h>
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#include <linux/filter.h>
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#include "libbpf.h"
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#include "bpf_helpers.h"
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#include "bpf_load.h"
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static char license[128];
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static bool processed_sec[128];
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int map_fd[MAX_MAPS];
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int prog_fd[MAX_PROGS];
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int prog_cnt;
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static int load_and_attach(const char *event, struct bpf_insn *prog, int size)
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{
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int fd;
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bool is_socket = strncmp(event, "socket", 6) == 0;
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if (!is_socket)
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/* tracing events tbd */
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return -1;
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fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER,
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prog, size, license);
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if (fd < 0) {
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printf("bpf_prog_load() err=%d\n%s", errno, bpf_log_buf);
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return -1;
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}
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prog_fd[prog_cnt++] = fd;
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return 0;
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}
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static int load_maps(struct bpf_map_def *maps, int len)
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{
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int i;
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for (i = 0; i < len / sizeof(struct bpf_map_def); i++) {
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map_fd[i] = bpf_create_map(maps[i].type,
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maps[i].key_size,
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maps[i].value_size,
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maps[i].max_entries);
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if (map_fd[i] < 0)
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return 1;
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}
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return 0;
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}
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static int get_sec(Elf *elf, int i, GElf_Ehdr *ehdr, char **shname,
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GElf_Shdr *shdr, Elf_Data **data)
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{
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Elf_Scn *scn;
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scn = elf_getscn(elf, i);
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if (!scn)
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return 1;
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if (gelf_getshdr(scn, shdr) != shdr)
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return 2;
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*shname = elf_strptr(elf, ehdr->e_shstrndx, shdr->sh_name);
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if (!*shname || !shdr->sh_size)
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return 3;
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*data = elf_getdata(scn, 0);
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if (!*data || elf_getdata(scn, *data) != NULL)
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return 4;
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return 0;
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}
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static int parse_relo_and_apply(Elf_Data *data, Elf_Data *symbols,
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GElf_Shdr *shdr, struct bpf_insn *insn)
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{
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int i, nrels;
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nrels = shdr->sh_size / shdr->sh_entsize;
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for (i = 0; i < nrels; i++) {
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GElf_Sym sym;
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GElf_Rel rel;
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unsigned int insn_idx;
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gelf_getrel(data, i, &rel);
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insn_idx = rel.r_offset / sizeof(struct bpf_insn);
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gelf_getsym(symbols, GELF_R_SYM(rel.r_info), &sym);
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if (insn[insn_idx].code != (BPF_LD | BPF_IMM | BPF_DW)) {
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printf("invalid relo for insn[%d].code 0x%x\n",
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insn_idx, insn[insn_idx].code);
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return 1;
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}
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insn[insn_idx].src_reg = BPF_PSEUDO_MAP_FD;
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insn[insn_idx].imm = map_fd[sym.st_value / sizeof(struct bpf_map_def)];
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}
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return 0;
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}
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int load_bpf_file(char *path)
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{
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int fd, i;
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Elf *elf;
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GElf_Ehdr ehdr;
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GElf_Shdr shdr, shdr_prog;
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Elf_Data *data, *data_prog, *symbols = NULL;
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char *shname, *shname_prog;
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if (elf_version(EV_CURRENT) == EV_NONE)
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return 1;
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fd = open(path, O_RDONLY, 0);
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if (fd < 0)
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return 1;
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elf = elf_begin(fd, ELF_C_READ, NULL);
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if (!elf)
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return 1;
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if (gelf_getehdr(elf, &ehdr) != &ehdr)
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return 1;
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/* scan over all elf sections to get license and map info */
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for (i = 1; i < ehdr.e_shnum; i++) {
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if (get_sec(elf, i, &ehdr, &shname, &shdr, &data))
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continue;
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if (0) /* helpful for llvm debugging */
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printf("section %d:%s data %p size %zd link %d flags %d\n",
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i, shname, data->d_buf, data->d_size,
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shdr.sh_link, (int) shdr.sh_flags);
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if (strcmp(shname, "license") == 0) {
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processed_sec[i] = true;
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memcpy(license, data->d_buf, data->d_size);
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} else if (strcmp(shname, "maps") == 0) {
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processed_sec[i] = true;
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if (load_maps(data->d_buf, data->d_size))
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return 1;
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} else if (shdr.sh_type == SHT_SYMTAB) {
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symbols = data;
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}
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}
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/* load programs that need map fixup (relocations) */
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for (i = 1; i < ehdr.e_shnum; i++) {
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if (get_sec(elf, i, &ehdr, &shname, &shdr, &data))
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continue;
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if (shdr.sh_type == SHT_REL) {
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struct bpf_insn *insns;
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if (get_sec(elf, shdr.sh_info, &ehdr, &shname_prog,
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&shdr_prog, &data_prog))
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continue;
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insns = (struct bpf_insn *) data_prog->d_buf;
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processed_sec[shdr.sh_info] = true;
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processed_sec[i] = true;
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if (parse_relo_and_apply(data, symbols, &shdr, insns))
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continue;
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if (memcmp(shname_prog, "events/", 7) == 0 ||
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memcmp(shname_prog, "socket", 6) == 0)
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load_and_attach(shname_prog, insns, data_prog->d_size);
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}
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}
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/* load programs that don't use maps */
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for (i = 1; i < ehdr.e_shnum; i++) {
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if (processed_sec[i])
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continue;
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if (get_sec(elf, i, &ehdr, &shname, &shdr, &data))
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continue;
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if (memcmp(shname, "events/", 7) == 0 ||
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memcmp(shname, "socket", 6) == 0)
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load_and_attach(shname, data->d_buf, data->d_size);
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}
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close(fd);
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return 0;
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}
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@ -0,0 +1,24 @@
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#ifndef __BPF_LOAD_H
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#define __BPF_LOAD_H
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#define MAX_MAPS 32
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#define MAX_PROGS 32
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extern int map_fd[MAX_MAPS];
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extern int prog_fd[MAX_PROGS];
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/* parses elf file compiled by llvm .c->.o
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* . parses 'maps' section and creates maps via BPF syscall
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* . parses 'license' section and passes it to syscall
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* . parses elf relocations for BPF maps and adjusts BPF_LD_IMM64 insns by
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* storing map_fd into insn->imm and marking such insns as BPF_PSEUDO_MAP_FD
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* . loads eBPF programs via BPF syscall
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*
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* One ELF file can contain multiple BPF programs which will be loaded
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* and their FDs stored stored in prog_fd array
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*
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* returns zero on success
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*/
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int load_bpf_file(char *path);
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#endif
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