bpf: implement btf handling and map annotation

Implement loading of .BTF section from object file and build up
internal table for retrieving key/value id related to maps in
the BPF program. Latter is done by setting up struct btf_type
table.

One of the issues is that there's a disconnect between the data
types used in the map and struct bpf_elf_map, meaning the underlying
types are unknown from the map description. One way to overcome
this is to add a annotation such that the loader will recognize
the relation to both. BPF_ANNOTATE_KV_PAIR(map_foo, struct key,
struct val); has been added to the API that programs can use.

The loader will then pick the corresponding key/value type ids and
attach it to the maps for creation. This can later on be dumped via
bpftool for introspection.

Example with test_xdp_noinline.o from kernel selftests:

  [...]

  struct ctl_value {
        union {
                __u64 value;
                __u32 ifindex;
                __u8 mac[6];
        };
  };

  struct bpf_map_def __attribute__ ((section("maps"), used)) ctl_array = {
        .type		= BPF_MAP_TYPE_ARRAY,
        .key_size	= sizeof(__u32),
        .value_size	= sizeof(struct ctl_value),
        .max_entries	= 16,
        .map_flags	= 0,
  };
  BPF_ANNOTATE_KV_PAIR(ctl_array, __u32, struct ctl_value);

  [...]

Above could also further be wrapped in a macro. Compiling through LLVM and
converting to BTF:

  # llc --version
  LLVM (http://llvm.org/):
    LLVM version 7.0.0svn
    Optimized build.
    Default target: x86_64-unknown-linux-gnu
    Host CPU: skylake

    Registered Targets:
      bpf    - BPF (host endian)
      bpfeb  - BPF (big endian)
      bpfel  - BPF (little endian)
  [...]

  # clang [...] -O2 -target bpf -g -emit-llvm -c test_xdp_noinline.c -o - |
    llc -march=bpf -mcpu=probe -mattr=dwarfris -filetype=obj -o test_xdp_noinline.o
  # pahole -J test_xdp_noinline.o

Checking pahole dump of BPF object file:

  # file test_xdp_noinline.o
  test_xdp_noinline.o: ELF 64-bit LSB relocatable, *unknown arch 0xf7* version 1 (SYSV), with debug_info, not stripped
  # pahole test_xdp_noinline.o
  [...]
  struct ctl_value {
	union {
		__u64              value;                /*     0     8 */
		__u32              ifindex;              /*     0     4 */
		__u8               mac[0];               /*     0     0 */
	};                                               /*     0     8 */

	/* size: 8, cachelines: 1, members: 1 */
	/* last cacheline: 8 bytes */
  };

Now loading into kernel and dumping the map via bpftool:

  # ip -force link set dev lo xdp obj test_xdp_noinline.o sec xdp-test
  # ip a
  1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 xdpgeneric/id:227 qdisc noqueue state UNKNOWN group default qlen 1000
      link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
      inet 127.0.0.1/8 scope host lo
         valid_lft forever preferred_lft forever
      inet6 ::1/128 scope host
         valid_lft forever preferred_lft forever
  [...]
  # bpftool prog show id 227
  227: xdp  tag a85e060c275c5616  gpl
      loaded_at 2018-07-17T14:41:29+0000  uid 0
      xlated 8152B  not jited  memlock 12288B  map_ids 381,385,386,382,384,383
  # bpftool map dump id 386
   [{
        "key": 0,
        "value": {
            "": {
                "value": 0,
                "ifindex": 0,
                "mac": []
            }
        }
    },{
        "key": 1,
        "value": {
            "": {
                "value": 0,
                "ifindex": 0,
                "mac": []
            }
        }
    },{
  [...]

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David Ahern <dsahern@gmail.com>
This commit is contained in:
Daniel Borkmann 2018-07-18 01:31:22 +02:00 committed by David Ahern
parent b5cb33aec6
commit f823f36012
3 changed files with 338 additions and 4 deletions

View File

@ -41,4 +41,13 @@ struct bpf_elf_map {
__u32 inner_idx;
};
#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 = { }
#endif /* __BPF_ELF__ */

View File

@ -14,6 +14,7 @@
#define __BPF_UTIL__
#include <linux/bpf.h>
#include <linux/btf.h>
#include <linux/filter.h>
#include <linux/magic.h>
#include <linux/elf-em.h>

332
lib/bpf.c
View File

@ -388,6 +388,8 @@ struct bpf_prog_data {
struct bpf_map_ext {
struct bpf_prog_data owner;
unsigned int btf_id_key;
unsigned int btf_id_val;
};
static int bpf_derive_elf_map_from_fdinfo(int fd, struct bpf_elf_map *map,
@ -1120,24 +1122,36 @@ struct bpf_config {
unsigned int jit_enabled;
};
struct bpf_btf {
const struct btf_header *hdr;
const void *raw;
const char *strings;
const struct btf_type **types;
int types_num;
};
struct bpf_elf_ctx {
struct bpf_config cfg;
Elf *elf_fd;
GElf_Ehdr elf_hdr;
Elf_Data *sym_tab;
Elf_Data *str_tab;
Elf_Data *btf_data;
char obj_uid[64];
int obj_fd;
int btf_fd;
int map_fds[ELF_MAX_MAPS];
struct bpf_elf_map maps[ELF_MAX_MAPS];
struct bpf_map_ext maps_ext[ELF_MAX_MAPS];
struct bpf_elf_prog prog_text;
struct bpf_btf btf;
int sym_num;
int map_num;
int map_len;
bool *sec_done;
int sec_maps;
int sec_text;
int sec_btf;
char license[ELF_MAX_LICENSE_LEN];
enum bpf_prog_type type;
__u32 ifindex;
@ -1162,6 +1176,11 @@ struct bpf_map_data {
struct bpf_elf_map *ent;
};
static bool bpf_log_has_data(struct bpf_elf_ctx *ctx)
{
return ctx->log && ctx->log[0];
}
static __check_format_string(2, 3) void
bpf_dump_error(struct bpf_elf_ctx *ctx, const char *format, ...)
{
@ -1171,7 +1190,7 @@ bpf_dump_error(struct bpf_elf_ctx *ctx, const char *format, ...)
vfprintf(stderr, format, vl);
va_end(vl);
if (ctx->log && ctx->log[0]) {
if (bpf_log_has_data(ctx)) {
if (ctx->verbose) {
fprintf(stderr, "%s\n", ctx->log);
} else {
@ -1218,7 +1237,9 @@ static int bpf_log_realloc(struct bpf_elf_ctx *ctx)
static int bpf_map_create(enum bpf_map_type type, uint32_t size_key,
uint32_t size_value, uint32_t max_elem,
uint32_t flags, int inner_fd, uint32_t ifindex)
uint32_t flags, int inner_fd, int btf_fd,
uint32_t ifindex, uint32_t btf_id_key,
uint32_t btf_id_val)
{
union bpf_attr attr = {};
@ -1229,10 +1250,30 @@ static int bpf_map_create(enum bpf_map_type type, uint32_t size_key,
attr.map_flags = flags;
attr.inner_map_fd = inner_fd;
attr.map_ifindex = ifindex;
attr.btf_fd = btf_fd;
attr.btf_key_type_id = btf_id_key;
attr.btf_value_type_id = btf_id_val;
return bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
}
static int bpf_btf_load(void *btf, size_t size_btf,
char *log, size_t size_log)
{
union bpf_attr attr = {};
attr.btf = bpf_ptr_to_u64(btf);
attr.btf_size = size_btf;
if (size_log > 0) {
attr.btf_log_buf = bpf_ptr_to_u64(log);
attr.btf_log_size = size_log;
attr.btf_log_level = 1;
}
return bpf(BPF_BTF_LOAD, &attr, sizeof(attr));
}
static int bpf_obj_pin(int fd, const char *pathname)
{
union bpf_attr attr = {};
@ -1608,7 +1649,8 @@ static int bpf_map_attach(const char *name, struct bpf_elf_ctx *ctx,
ifindex = bpf_map_offload_neutral(map->type) ? 0 : ctx->ifindex;
errno = 0;
fd = bpf_map_create(map->type, map->size_key, map->size_value,
map->max_elem, map->flags, map_inner_fd, ifindex);
map->max_elem, map->flags, map_inner_fd, ctx->btf_fd,
ifindex, ext->btf_id_key, ext->btf_id_val);
if (fd < 0 || ctx->verbose) {
bpf_map_report(fd, name, map, ctx, map_inner_fd);
@ -1633,8 +1675,80 @@ static const char *bpf_str_tab_name(const struct bpf_elf_ctx *ctx,
return ctx->str_tab->d_buf + sym->st_name;
}
static int bpf_btf_find(struct bpf_elf_ctx *ctx, const char *name)
{
const struct btf_type *type;
const char *res;
int id;
for (id = 1; id < ctx->btf.types_num; id++) {
type = ctx->btf.types[id];
if (type->name_off >= ctx->btf.hdr->str_len)
continue;
res = &ctx->btf.strings[type->name_off];
if (!strcmp(res, name))
return id;
}
return -ENOENT;
}
static int bpf_btf_find_kv(struct bpf_elf_ctx *ctx, const struct bpf_elf_map *map,
const char *name, uint32_t *id_key, uint32_t *id_val)
{
const struct btf_member *key, *val;
const struct btf_type *type;
char btf_name[512];
const char *res;
int id;
snprintf(btf_name, sizeof(btf_name), "____btf_map_%s", name);
id = bpf_btf_find(ctx, btf_name);
if (id < 0)
return id;
type = ctx->btf.types[id];
if (BTF_INFO_KIND(type->info) != BTF_KIND_STRUCT)
return -EINVAL;
if (BTF_INFO_VLEN(type->info) != 2)
return -EINVAL;
key = ((void *) type) + sizeof(*type);
val = key + 1;
if (!key->type || key->type >= ctx->btf.types_num ||
!val->type || val->type >= ctx->btf.types_num)
return -EINVAL;
if (key->name_off >= ctx->btf.hdr->str_len ||
val->name_off >= ctx->btf.hdr->str_len)
return -EINVAL;
res = &ctx->btf.strings[key->name_off];
if (strcmp(res, "key"))
return -EINVAL;
res = &ctx->btf.strings[val->name_off];
if (strcmp(res, "value"))
return -EINVAL;
*id_key = key->type;
*id_val = val->type;
return 0;
}
static void bpf_btf_annotate(struct bpf_elf_ctx *ctx, int which, const char *name)
{
uint32_t id_key = 0, id_val = 0;
if (!bpf_btf_find_kv(ctx, &ctx->maps[which], name, &id_key, &id_val)) {
ctx->maps_ext[which].btf_id_key = id_key;
ctx->maps_ext[which].btf_id_val = id_val;
}
}
static const char *bpf_map_fetch_name(struct bpf_elf_ctx *ctx, int which)
{
const char *name;
GElf_Sym sym;
int i;
@ -1648,7 +1762,9 @@ static const char *bpf_map_fetch_name(struct bpf_elf_ctx *ctx, int which)
sym.st_value / ctx->map_len != which)
continue;
return bpf_str_tab_name(ctx, &sym);
name = bpf_str_tab_name(ctx, &sym);
bpf_btf_annotate(ctx, which, name);
return name;
}
return NULL;
@ -1910,11 +2026,210 @@ static int bpf_fetch_text(struct bpf_elf_ctx *ctx, int section,
return 0;
}
static void bpf_btf_report(int fd, struct bpf_elf_ctx *ctx)
{
fprintf(stderr, "\nBTF debug data section \'.BTF\' %s%s (%d)!\n",
fd < 0 ? "rejected: " : "loaded",
fd < 0 ? strerror(errno) : "",
fd < 0 ? errno : fd);
fprintf(stderr, " - Length: %zu\n", ctx->btf_data->d_size);
bpf_dump_error(ctx, "Verifier analysis:\n\n");
}
static int bpf_btf_attach(struct bpf_elf_ctx *ctx)
{
int tries = 0, fd;
retry:
errno = 0;
fd = bpf_btf_load(ctx->btf_data->d_buf, ctx->btf_data->d_size,
ctx->log, ctx->log_size);
if (fd < 0 || ctx->verbose) {
if (fd < 0 && (errno == ENOSPC || !ctx->log_size)) {
if (tries++ < 10 && !bpf_log_realloc(ctx))
goto retry;
fprintf(stderr, "Log buffer too small to dump verifier log %zu bytes (%d tries)!\n",
ctx->log_size, tries);
return fd;
}
if (bpf_log_has_data(ctx))
bpf_btf_report(fd, ctx);
}
return fd;
}
static int bpf_fetch_btf_begin(struct bpf_elf_ctx *ctx, int section,
struct bpf_elf_sec_data *data)
{
ctx->btf_data = data->sec_data;
ctx->sec_btf = section;
ctx->sec_done[section] = true;
return 0;
}
static int bpf_btf_check_header(struct bpf_elf_ctx *ctx)
{
const struct btf_header *hdr = ctx->btf_data->d_buf;
const char *str_start, *str_end;
unsigned int data_len;
if (hdr->magic != BTF_MAGIC) {
fprintf(stderr, "Object has wrong BTF magic: %x, expected: %x!\n",
hdr->magic, BTF_MAGIC);
return -EINVAL;
}
if (hdr->version != BTF_VERSION) {
fprintf(stderr, "Object has wrong BTF version: %u, expected: %u!\n",
hdr->version, BTF_VERSION);
return -EINVAL;
}
if (hdr->flags) {
fprintf(stderr, "Object has unsupported BTF flags %x!\n",
hdr->flags);
return -EINVAL;
}
data_len = ctx->btf_data->d_size - sizeof(*hdr);
if (data_len < hdr->type_off ||
data_len < hdr->str_off ||
data_len < hdr->type_len + hdr->str_len ||
hdr->type_off >= hdr->str_off ||
hdr->type_off + hdr->type_len != hdr->str_off ||
hdr->str_off + hdr->str_len != data_len ||
(hdr->type_off & (sizeof(uint32_t) - 1))) {
fprintf(stderr, "Object has malformed BTF data!\n");
return -EINVAL;
}
ctx->btf.hdr = hdr;
ctx->btf.raw = hdr + 1;
str_start = ctx->btf.raw + hdr->str_off;
str_end = str_start + hdr->str_len;
if (!hdr->str_len ||
hdr->str_len - 1 > BTF_MAX_NAME_OFFSET ||
str_start[0] || str_end[-1]) {
fprintf(stderr, "Object has malformed BTF string data!\n");
return -EINVAL;
}
ctx->btf.strings = str_start;
return 0;
}
static int bpf_btf_register_type(struct bpf_elf_ctx *ctx,
const struct btf_type *type)
{
int cur = ctx->btf.types_num, num = cur + 1;
const struct btf_type **types;
types = realloc(ctx->btf.types, num * sizeof(type));
if (!types) {
free(ctx->btf.types);
ctx->btf.types = NULL;
ctx->btf.types_num = 0;
return -ENOMEM;
}
ctx->btf.types = types;
ctx->btf.types[cur] = type;
ctx->btf.types_num = num;
return 0;
}
static struct btf_type btf_type_void;
static int bpf_btf_prep_type_data(struct bpf_elf_ctx *ctx)
{
const void *type_cur = ctx->btf.raw + ctx->btf.hdr->type_off;
const void *type_end = ctx->btf.raw + ctx->btf.hdr->str_off;
const struct btf_type *type;
uint16_t var_len;
int ret, kind;
ret = bpf_btf_register_type(ctx, &btf_type_void);
if (ret < 0)
return ret;
while (type_cur < type_end) {
type = type_cur;
type_cur += sizeof(*type);
var_len = BTF_INFO_VLEN(type->info);
kind = BTF_INFO_KIND(type->info);
switch (kind) {
case BTF_KIND_INT:
type_cur += sizeof(int);
break;
case BTF_KIND_ARRAY:
type_cur += sizeof(struct btf_array);
break;
case BTF_KIND_STRUCT:
case BTF_KIND_UNION:
type_cur += var_len * sizeof(struct btf_member);
break;
case BTF_KIND_ENUM:
type_cur += var_len * sizeof(struct btf_enum);
break;
case BTF_KIND_TYPEDEF:
case BTF_KIND_PTR:
case BTF_KIND_FWD:
case BTF_KIND_VOLATILE:
case BTF_KIND_CONST:
case BTF_KIND_RESTRICT:
break;
default:
fprintf(stderr, "Object has unknown BTF type: %u!\n", kind);
return -EINVAL;
}
ret = bpf_btf_register_type(ctx, type);
if (ret < 0)
return ret;
}
return 0;
}
static int bpf_btf_prep_data(struct bpf_elf_ctx *ctx)
{
int ret = bpf_btf_check_header(ctx);
if (!ret)
return bpf_btf_prep_type_data(ctx);
return ret;
}
static void bpf_fetch_btf_end(struct bpf_elf_ctx *ctx)
{
int fd = bpf_btf_attach(ctx);
if (fd < 0)
return;
ctx->btf_fd = fd;
if (bpf_btf_prep_data(ctx) < 0) {
close(ctx->btf_fd);
ctx->btf_fd = 0;
}
}
static bool bpf_has_map_data(const struct bpf_elf_ctx *ctx)
{
return ctx->sym_tab && ctx->str_tab && ctx->sec_maps;
}
static bool bpf_has_btf_data(const struct bpf_elf_ctx *ctx)
{
return ctx->sec_btf;
}
static bool bpf_has_call_data(const struct bpf_elf_ctx *ctx)
{
return ctx->sec_text;
@ -1947,6 +2262,9 @@ static int bpf_fetch_ancillary(struct bpf_elf_ctx *ctx, bool check_text_sec)
else if (data.sec_hdr.sh_type == SHT_STRTAB &&
!strcmp(data.sec_name, ".strtab"))
ret = bpf_fetch_strtab(ctx, i, &data);
else if (data.sec_hdr.sh_type == SHT_PROGBITS &&
!strcmp(data.sec_name, ".BTF"))
ret = bpf_fetch_btf_begin(ctx, i, &data);
if (ret < 0) {
fprintf(stderr, "Error parsing section %d! Perhaps check with readelf -a?\n",
i);
@ -1954,6 +2272,8 @@ static int bpf_fetch_ancillary(struct bpf_elf_ctx *ctx, bool check_text_sec)
}
}
if (bpf_has_btf_data(ctx))
bpf_fetch_btf_end(ctx);
if (bpf_has_map_data(ctx)) {
ret = bpf_fetch_maps_end(ctx);
if (ret < 0) {
@ -2591,6 +2911,10 @@ static void bpf_maps_teardown(struct bpf_elf_ctx *ctx)
if (ctx->map_fds[i])
close(ctx->map_fds[i]);
}
if (ctx->btf_fd)
close(ctx->btf_fd);
free(ctx->btf.types);
}
static void bpf_elf_ctx_destroy(struct bpf_elf_ctx *ctx, bool failure)