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libbpf: Don't require root for bpf_object__open()
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Reorganize bpf_object__open and bpf_object__load steps such that
bpf_object__open doesn't need root access. This was previously done for
feature probing and BTF sanitization. This doesn't have to happen on open,
though, so move all those steps into the load phase.

This is important, because it makes it possible for tools like bpftool, to
just open BPF object file and inspect their contents: programs, maps, BTF,
etc. For such operations it is prohibitive to require root access. On the
other hand, there is a lot of custom libbpf logic in those steps, so its best
avoided for tools to reimplement all that on their own.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20191214014341.3442258-2-andriin@fb.com
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Andrii Nakryiko authored and Alexei Starovoitov committed Dec 15, 2019
1 parent aa91593 commit 0d13bfc
Showing 1 changed file with 41 additions and 42 deletions.
83 changes: 41 additions & 42 deletions tools/lib/bpf/libbpf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -101,13 +101,6 @@ void libbpf_print(enum libbpf_print_level level, const char *format, ...)

#define STRERR_BUFSIZE 128

#define CHECK_ERR(action, err, out) do { \
err = action; \
if (err) \
goto out; \
} while (0)


/* Copied from tools/perf/util/util.h */
#ifndef zfree
# define zfree(ptr) ({ free(*ptr); *ptr = NULL; })
Expand Down Expand Up @@ -864,8 +857,7 @@ bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type,
def->value_size = data->d_size;
def->max_entries = 1;
def->map_flags = type == LIBBPF_MAP_RODATA ? BPF_F_RDONLY_PROG : 0;
if (obj->caps.array_mmap)
def->map_flags |= BPF_F_MMAPABLE;
def->map_flags |= BPF_F_MMAPABLE;

pr_debug("map '%s' (global data): at sec_idx %d, offset %zu, flags %x.\n",
map_name, map->sec_idx, map->sec_offset, def->map_flags);
Expand All @@ -888,8 +880,6 @@ static int bpf_object__init_global_data_maps(struct bpf_object *obj)
{
int err;

if (!obj->caps.global_data)
return 0;
/*
* Populate obj->maps with libbpf internal maps.
*/
Expand Down Expand Up @@ -1393,10 +1383,11 @@ static int bpf_object__init_user_btf_maps(struct bpf_object *obj, bool strict,
return 0;
}

static int bpf_object__init_maps(struct bpf_object *obj, bool relaxed_maps,
const char *pin_root_path)
static int bpf_object__init_maps(struct bpf_object *obj,
struct bpf_object_open_opts *opts)
{
bool strict = !relaxed_maps;
const char *pin_root_path = OPTS_GET(opts, pin_root_path, NULL);
bool strict = !OPTS_GET(opts, relaxed_maps, false);
int err;

err = bpf_object__init_user_maps(obj, strict);
Expand Down Expand Up @@ -1592,8 +1583,7 @@ static int bpf_object__sanitize_and_load_btf(struct bpf_object *obj)
return 0;
}

static int bpf_object__elf_collect(struct bpf_object *obj, bool relaxed_maps,
const char *pin_root_path)
static int bpf_object__elf_collect(struct bpf_object *obj)
{
Elf *elf = obj->efile.elf;
GElf_Ehdr *ep = &obj->efile.ehdr;
Expand Down Expand Up @@ -1728,14 +1718,7 @@ static int bpf_object__elf_collect(struct bpf_object *obj, bool relaxed_maps,
pr_warn("Corrupted ELF file: index of strtab invalid\n");
return -LIBBPF_ERRNO__FORMAT;
}
err = bpf_object__init_btf(obj, btf_data, btf_ext_data);
if (!err)
err = bpf_object__init_maps(obj, relaxed_maps, pin_root_path);
if (!err)
err = bpf_object__sanitize_and_load_btf(obj);
if (!err)
err = bpf_object__init_prog_names(obj);
return err;
return bpf_object__init_btf(obj, btf_data, btf_ext_data);
}

static struct bpf_program *
Expand Down Expand Up @@ -1876,11 +1859,6 @@ static int bpf_program__record_reloc(struct bpf_program *prog,
pr_warn("bad data relo against section %u\n", shdr_idx);
return -LIBBPF_ERRNO__RELOC;
}
if (!obj->caps.global_data) {
pr_warn("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++) {
map = &obj->maps[map_idx];
if (map->libbpf_type != type)
Expand Down Expand Up @@ -3918,12 +3896,10 @@ static struct bpf_object *
__bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
struct bpf_object_open_opts *opts)
{
const char *pin_root_path;
struct bpf_program *prog;
struct bpf_object *obj;
const char *obj_name;
char tmp_name[64];
bool relaxed_maps;
__u32 attach_prog_fd;
int err;

Expand Down Expand Up @@ -3953,16 +3929,16 @@ __bpf_object__open(const char *path, const void *obj_buf, size_t obj_buf_sz,
return obj;

obj->relaxed_core_relocs = OPTS_GET(opts, relaxed_core_relocs, false);
relaxed_maps = OPTS_GET(opts, relaxed_maps, false);
pin_root_path = OPTS_GET(opts, pin_root_path, NULL);
attach_prog_fd = OPTS_GET(opts, attach_prog_fd, 0);

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, relaxed_maps, pin_root_path),
err, out);
CHECK_ERR(bpf_object__collect_reloc(obj), err, out);
err = bpf_object__elf_init(obj);
err = err ? : bpf_object__check_endianness(obj);
err = err ? : bpf_object__elf_collect(obj);
err = err ? : bpf_object__init_maps(obj, opts);
err = err ? : bpf_object__init_prog_names(obj);
err = err ? : bpf_object__collect_reloc(obj);
if (err)
goto out;
bpf_object__elf_finish(obj);

bpf_object__for_each_program(prog, obj) {
Expand Down Expand Up @@ -4080,6 +4056,24 @@ int bpf_object__unload(struct bpf_object *obj)
return 0;
}

static int bpf_object__sanitize_maps(struct bpf_object *obj)
{
struct bpf_map *m;

bpf_object__for_each_map(m, obj) {
if (!bpf_map__is_internal(m))
continue;
if (!obj->caps.global_data) {
pr_warn("kernel doesn't support global data\n");
return -ENOTSUP;
}
if (!obj->caps.array_mmap)
m->def.map_flags ^= BPF_F_MMAPABLE;
}

return 0;
}

int bpf_object__load_xattr(struct bpf_object_load_attr *attr)
{
struct bpf_object *obj;
Expand All @@ -4098,9 +4092,14 @@ int bpf_object__load_xattr(struct bpf_object_load_attr *attr)

obj->loaded = true;

CHECK_ERR(bpf_object__create_maps(obj), err, out);
CHECK_ERR(bpf_object__relocate(obj, attr->target_btf_path), err, out);
CHECK_ERR(bpf_object__load_progs(obj, attr->log_level), err, out);
err = bpf_object__probe_caps(obj);
err = err ? : bpf_object__sanitize_and_load_btf(obj);
err = err ? : bpf_object__sanitize_maps(obj);
err = err ? : bpf_object__create_maps(obj);
err = err ? : bpf_object__relocate(obj, attr->target_btf_path);
err = err ? : bpf_object__load_progs(obj, attr->log_level);
if (err)
goto out;

return 0;
out:
Expand Down

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