Commit aea28a60 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
Browse files

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



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: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210423181348.1801389-5-andrii@kernel.org
parent 0fec7a3c

tools/lib/bpf/bpf_helpers.h

+8 −0
Original line number Diff line number Diff line
@@ -47,6 +47,14 @@ 
#define __weak __attribute__((weak))

#endif



/*

 * Use __hidden attribute to mark a non-static BPF subprogram effectively

 * static for BPF verifier's verification algorithm purposes, allowing more

 * extensive and permissive BPF verification process, taking into account

 * subprogram's caller context.

 */

#define __hidden __attribute__((visibility("hidden")))



/* When utilizing vmlinux.h with BPF CO-RE, user BPF programs can't include

 * any system-level headers (such as stddef.h, linux/version.h, etc), and

 * commonly-used macros like NULL and KERNEL_VERSION aren't available through

tools/lib/bpf/btf.c

+0 −5
Original line number Diff line number Diff line
@@ -1605,11 +1605,6 @@ static void *btf_add_type_mem(struct btf *btf, size_t add_sz) 
			      btf->hdr->type_len, UINT_MAX, add_sz);

}



static __u32 btf_type_info(int kind, int vlen, int kflag)

{

	return (kflag << 31) | (kind << 24) | vlen;

}



static void btf_type_inc_vlen(struct btf_type *t)

{

	t->info = btf_type_info(btf_kind(t), btf_vlen(t) + 1, btf_kflag(t));

tools/lib/bpf/libbpf.c

+44 −1
Original line number Diff line number Diff line
@@ -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;

tools/lib/bpf/libbpf_internal.h

+6 −0
Original line number Diff line number Diff line
@@ -19,6 +19,7 @@ 
#pragma GCC poison reallocarray



#include "libbpf.h"

#include "btf.h"



#ifndef EM_BPF

#define EM_BPF 247
@@ -132,6 +133,11 @@ struct btf_type; 


struct btf_type *btf_type_by_id(struct btf *btf, __u32 type_id);



static inline __u32 btf_type_info(int kind, int vlen, int kflag)

{

	return (kflag << 31) | (kind << 24) | vlen;

}



void *libbpf_add_mem(void **data, size_t *cap_cnt, size_t elem_sz,

		     size_t cur_cnt, size_t max_cnt, size_t add_cnt);

int libbpf_ensure_mem(void **data, size_t *cap_cnt, size_t elem_sz, size_t need_cnt);