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bpf, libbpf: handle old kernels more graceful wrt global data sections

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Andrii reported a corner case where e.g. global static data is present
in the BPF ELF file in form of .data/.bss/.rodata section, but without
any relocations to it. Such programs could be loaded before commit
d859900c4c ("bpf, libbpf: support global data/bss/rodata sections"),
whereas afterwards if kernel lacks support then loading would fail.

Add a probing mechanism which skips setting up libbpf internal maps
in case of missing kernel support. In presence of relocation entries,
we abort the load attempt.

Fixes: d859900c4c ("bpf, libbpf: support global data/bss/rodata sections")
Reported-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Daniel Borkmann 2019-04-24 00:45:56 +02:00 committed by Alexei Starovoitov
parent a21b48a2f2
commit 8837fe5dd0
1 changed files with 86 additions and 13 deletions
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99
tools/lib/bpf/libbpf.c
View File

@ -126,6 +126,8 @@ static inline __u64 ptr_to_u64(const void *ptr)
struct bpf_capabilities {
/* v4.14: kernel support for program & map names. */
__u32 name:1;
/* v5.2: kernel support for global data sections. */
__u32 global_data:1;
};
/*
@ -854,12 +856,15 @@ bpf_object__init_maps(struct bpf_object *obj, int flags)
*
* TODO: Detect array of map and report error.
*/
if (obj->efile.data_shndx >= 0)
nr_maps_glob++;
if (obj->efile.rodata_shndx >= 0)
nr_maps_glob++;
if (obj->efile.bss_shndx >= 0)
nr_maps_glob++;
if (obj->caps.global_data) {
if (obj->efile.data_shndx >= 0)
nr_maps_glob++;
if (obj->efile.rodata_shndx >= 0)
nr_maps_glob++;
if (obj->efile.bss_shndx >= 0)
nr_maps_glob++;
}
for (i = 0; data && i < nr_syms; i++) {
GElf_Sym sym;
@ -971,6 +976,9 @@ bpf_object__init_maps(struct bpf_object *obj, int flags)
map_idx++;
}
if (!obj->caps.global_data)
goto finalize;
/*
* Populate rest of obj->maps with libbpf internal maps.
*/
@ -988,6 +996,7 @@ bpf_object__init_maps(struct bpf_object *obj, int flags)
ret = bpf_object__init_internal_map(obj, &obj->maps[map_idx++],
LIBBPF_MAP_BSS,
obj->efile.bss, NULL);
finalize:
if (!ret)
qsort(obj->maps, obj->nr_maps, sizeof(obj->maps[0]),
compare_bpf_map);
@ -1333,11 +1342,17 @@ bpf_program__collect_reloc(struct bpf_program *prog, GElf_Shdr *shdr,
if (bpf_object__shndx_is_maps(obj, shdr_idx) ||
bpf_object__shndx_is_data(obj, shdr_idx)) {
type = bpf_object__section_to_libbpf_map_type(obj, shdr_idx);
if (type != LIBBPF_MAP_UNSPEC &&
GELF_ST_BIND(sym.st_info) == STB_GLOBAL) {
pr_warning("bpf: relocation: not yet supported relo for non-static global \'%s\' variable found in insns[%d].code 0x%x\n",
name, insn_idx, insns[insn_idx].code);
return -LIBBPF_ERRNO__RELOC;
if (type != LIBBPF_MAP_UNSPEC) {
if (GELF_ST_BIND(sym.st_info) == STB_GLOBAL) {
pr_warning("bpf: relocation: not yet supported relo for non-static global \'%s\' variable found in insns[%d].code 0x%x\n",
name, insn_idx, insns[insn_idx].code);
return -LIBBPF_ERRNO__RELOC;
}
if (!obj->caps.global_data) {
pr_warning("bpf: relocation: kernel does not support global \'%s\' variable access in insns[%d]\n",
name, insn_idx);
return -LIBBPF_ERRNO__RELOC;
}
}
for (map_idx = 0; map_idx < nr_maps; map_idx++) {
@ -1495,10 +1510,68 @@ bpf_object__probe_name(struct bpf_object *obj)
return 0;
}
static int
bpf_object__probe_global_data(struct bpf_object *obj)
{
struct bpf_load_program_attr prg_attr;
struct bpf_create_map_attr map_attr;
char *cp, errmsg[STRERR_BUFSIZE];
struct bpf_insn insns[] = {
BPF_LD_MAP_VALUE(BPF_REG_1, 0, 16),
BPF_ST_MEM(BPF_DW, BPF_REG_1, 0, 42),
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_EXIT_INSN(),
};
int ret, map;
memset(&map_attr, 0, sizeof(map_attr));
map_attr.map_type = BPF_MAP_TYPE_ARRAY;
map_attr.key_size = sizeof(int);
map_attr.value_size = 32;
map_attr.max_entries = 1;
map = bpf_create_map_xattr(&map_attr);
if (map < 0) {
cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
pr_warning("Error in %s():%s(%d). Couldn't create simple array map.\n",
__func__, cp, errno);
return -errno;
}
insns[0].imm = map;
memset(&prg_attr, 0, sizeof(prg_attr));
prg_attr.prog_type = BPF_PROG_TYPE_SOCKET_FILTER;
prg_attr.insns = insns;
prg_attr.insns_cnt = ARRAY_SIZE(insns);
prg_attr.license = "GPL";
ret = bpf_load_program_xattr(&prg_attr, NULL, 0);
if (ret >= 0) {
obj->caps.global_data = 1;
close(ret);
}
close(map);
return 0;
}
static int
bpf_object__probe_caps(struct bpf_object *obj)
{
return bpf_object__probe_name(obj);
int (*probe_fn[])(struct bpf_object *obj) = {
bpf_object__probe_name,
bpf_object__probe_global_data,
};
int i, ret;
for (i = 0; i < ARRAY_SIZE(probe_fn); i++) {
ret = probe_fn[i](obj);
if (ret < 0)
return ret;
}
return 0;
}
static int
@ -2100,6 +2173,7 @@ __bpf_object__open(const char *path, void *obj_buf, size_t obj_buf_sz,
CHECK_ERR(bpf_object__elf_init(obj), err, out);
CHECK_ERR(bpf_object__check_endianness(obj), err, out);
CHECK_ERR(bpf_object__probe_caps(obj), err, out);
CHECK_ERR(bpf_object__elf_collect(obj, flags), err, out);
CHECK_ERR(bpf_object__collect_reloc(obj), err, out);
CHECK_ERR(bpf_object__validate(obj, needs_kver), err, out);
@ -2193,7 +2267,6 @@ int bpf_object__load(struct bpf_object *obj)
obj->loaded = true;
CHECK_ERR(bpf_object__probe_caps(obj), err, out);
CHECK_ERR(bpf_object__create_maps(obj), err, out);
CHECK_ERR(bpf_object__relocate(obj), err, out);
CHECK_ERR(bpf_object__load_progs(obj), err, out);