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libbpf: Mark BPF subprogs with hidden visibility as static for BPF verifier

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Define __hidden helper macro in bpf_helpers.h, which is a short-hand for
__attribute__((visibility("hidden"))). Add libbpf support to mark BPF
subprograms marked with __hidden as static in BTF information to enforce BPF
verifier's static function validation algorithm, which takes more information
(caller's context) into account during a subprogram validation.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210423181348.1801389-5-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko
2021-04-23 11:13:34 -07:00
committed by Alexei Starovoitov
parent 0fec7a3cee
commit aea28a602f
4 changed files with 58 additions and 6 deletions
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45
tools/lib/bpf/libbpf.c
View File

@ -71,6 +71,7 @@
static struct bpf_map *bpf_object__add_map(struct bpf_object *obj);
static const struct btf_type *
skip_mods_and_typedefs(const struct btf *btf, __u32 id, __u32 *res_id);
static bool prog_is_subprog(const struct bpf_object *obj, const struct bpf_program *prog);
static int __base_pr(enum libbpf_print_level level, const char *format,
va_list args)
@ -274,6 +275,7 @@ struct bpf_program {
bpf_program_clear_priv_t clear_priv;
bool load;
bool mark_btf_static;
enum bpf_prog_type type;
enum bpf_attach_type expected_attach_type;
int prog_ifindex;
@ -698,6 +700,15 @@ bpf_object__add_programs(struct bpf_object *obj, Elf_Data *sec_data,
if (err)
return err;
/* if function is a global/weak symbol, but has hidden
* visibility (STV_HIDDEN), mark its BTF FUNC as static to
* enable more permissive BPF verification mode with more
* outside context available to BPF verifier
*/
if (GELF_ST_BIND(sym.st_info) != STB_LOCAL
&& GELF_ST_VISIBILITY(sym.st_other) == STV_HIDDEN)
prog->mark_btf_static = true;
nr_progs++;
obj->nr_programs = nr_progs;
@ -2618,7 +2629,7 @@ static int bpf_object__sanitize_and_load_btf(struct bpf_object *obj)
{
struct btf *kern_btf = obj->btf;
bool btf_mandatory, sanitize;
int err = 0;
int i, err = 0;
if (!obj->btf)
return 0;
@ -2632,6 +2643,38 @@ static int bpf_object__sanitize_and_load_btf(struct bpf_object *obj)
return 0;
}
/* Even though some subprogs are global/weak, user might prefer more
* permissive BPF verification process that BPF verifier performs for
* static functions, taking into account more context from the caller
* functions. In such case, they need to mark such subprogs with
* __attribute__((visibility("hidden"))) and libbpf will adjust
* corresponding FUNC BTF type to be marked as static and trigger more
* involved BPF verification process.
*/
for (i = 0; i < obj->nr_programs; i++) {
struct bpf_program *prog = &obj->programs[i];
struct btf_type *t;
const char *name;
int j, n;
if (!prog->mark_btf_static || !prog_is_subprog(obj, prog))
continue;
n = btf__get_nr_types(obj->btf);
for (j = 1; j <= n; j++) {
t = btf_type_by_id(obj->btf, j);
if (!btf_is_func(t) || btf_func_linkage(t) != BTF_FUNC_GLOBAL)
continue;
name = btf__str_by_offset(obj->btf, t->name_off);
if (strcmp(name, prog->name) != 0)
continue;
t->info = btf_type_info(BTF_KIND_FUNC, BTF_FUNC_STATIC, 0);
break;
}
}
sanitize = btf_needs_sanitization(obj);
if (sanitize) {
const void *raw_data;