Commit 5d23328d authored by YiFei Zhu's avatar YiFei Zhu Committed by Alexei Starovoitov
Browse files

libbpf: Add BPF_PROG_BIND_MAP syscall and use it on .rodata section 



The patch adds a simple wrapper bpf_prog_bind_map around the syscall.
When the libbpf tries to load a program, it will probe the kernel for
the support of this syscall and unconditionally bind .rodata section
to the program.

Signed-off-by: default avatarYiFei Zhu <zhuyifei@google.com>
Signed-off-by: default avatarStanislav Fomichev <sdf@google.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Cc: YiFei Zhu <zhuyifei1999@gmail.com>
Link: https://lore.kernel.org/bpf/20200915234543.3220146-4-sdf@google.com
parent ef15314a

tools/lib/bpf/bpf.c

+16 −0
Original line number Diff line number Diff line
@@ -872,3 +872,19 @@ int bpf_enable_stats(enum bpf_stats_type type) 


	return sys_bpf(BPF_ENABLE_STATS, &attr, sizeof(attr));

}



int bpf_prog_bind_map(int prog_fd, int map_fd,

		      const struct bpf_prog_bind_opts *opts)

{

	union bpf_attr attr;



	if (!OPTS_VALID(opts, bpf_prog_bind_opts))

		return -EINVAL;



	memset(&attr, 0, sizeof(attr));

	attr.prog_bind_map.prog_fd = prog_fd;

	attr.prog_bind_map.map_fd = map_fd;

	attr.prog_bind_map.flags = OPTS_GET(opts, flags, 0);



	return sys_bpf(BPF_PROG_BIND_MAP, &attr, sizeof(attr));

}

tools/lib/bpf/bpf.h

+8 −0
Original line number Diff line number Diff line
@@ -243,6 +243,14 @@ LIBBPF_API int bpf_task_fd_query(int pid, int fd, __u32 flags, char *buf, 
enum bpf_stats_type; /* defined in up-to-date linux/bpf.h */

LIBBPF_API int bpf_enable_stats(enum bpf_stats_type type);



struct bpf_prog_bind_opts {

	size_t sz; /* size of this struct for forward/backward compatibility */

	__u32 flags;

};

#define bpf_prog_bind_opts__last_field flags



LIBBPF_API int bpf_prog_bind_map(int prog_fd, int map_fd,

				 const struct bpf_prog_bind_opts *opts);

#ifdef __cplusplus

} /* extern "C" */

#endif

tools/lib/bpf/libbpf.c

+69 −0
Original line number Diff line number Diff line
@@ -174,6 +174,8 @@ enum kern_feature_id { 
	FEAT_EXP_ATTACH_TYPE,

	/* bpf_probe_read_{kernel,user}[_str] helpers */

	FEAT_PROBE_READ_KERN,

	/* BPF_PROG_BIND_MAP is supported */

	FEAT_PROG_BIND_MAP,

	__FEAT_CNT,

};
@@ -409,6 +411,7 @@ struct bpf_object { 
	struct extern_desc *externs;

	int nr_extern;

	int kconfig_map_idx;

	int rodata_map_idx;



	bool loaded;

	bool has_subcalls;
@@ -1070,6 +1073,7 @@ static struct bpf_object *bpf_object__new(const char *path, 
	obj->efile.bss_shndx = -1;

	obj->efile.st_ops_shndx = -1;

	obj->kconfig_map_idx = -1;

	obj->rodata_map_idx = -1;



	obj->kern_version = get_kernel_version();

	obj->loaded = false;
@@ -1428,6 +1432,8 @@ static int bpf_object__init_global_data_maps(struct bpf_object *obj) 
						    obj->efile.rodata->d_size);

		if (err)

			return err;



		obj->rodata_map_idx = obj->nr_maps - 1;

	}

	if (obj->efile.bss_shndx >= 0) {

		err = bpf_object__init_internal_map(obj, LIBBPF_MAP_BSS,
@@ -3894,6 +3900,52 @@ static int probe_kern_probe_read_kernel(void) 
	return probe_fd(bpf_load_program_xattr(&attr, NULL, 0));

}



static int probe_prog_bind_map(void)

{

	struct bpf_load_program_attr prg_attr;

	struct bpf_create_map_attr map_attr;

	char *cp, errmsg[STRERR_BUFSIZE];

	struct bpf_insn insns[] = {

		BPF_MOV64_IMM(BPF_REG_0, 0),

		BPF_EXIT_INSN(),

	};

	int ret, map, prog;



	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) {

		ret = -errno;

		cp = libbpf_strerror_r(ret, errmsg, sizeof(errmsg));

		pr_warn("Error in %s():%s(%d). Couldn't create simple array map.\n",

			__func__, cp, -ret);

		return ret;

	}



	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";



	prog = bpf_load_program_xattr(&prg_attr, NULL, 0);

	if (prog < 0) {

		close(map);

		return 0;

	}



	ret = bpf_prog_bind_map(prog, map, NULL);



	close(map);

	close(prog);



	return ret >= 0;

}



enum kern_feature_result {

	FEAT_UNKNOWN = 0,

	FEAT_SUPPORTED = 1,
@@ -3934,6 +3986,9 @@ static struct kern_feature_desc { 
	},

	[FEAT_PROBE_READ_KERN] = {

		"bpf_probe_read_kernel() helper", probe_kern_probe_read_kernel,

	},

	[FEAT_PROG_BIND_MAP] = {

		"BPF_PROG_BIND_MAP support", probe_prog_bind_map,

	}

};
@@ -6468,6 +6523,20 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt, 
	if (ret >= 0) {

		if (log_buf && load_attr.log_level)

			pr_debug("verifier log:\n%s", log_buf);



		if (prog->obj->rodata_map_idx >= 0 &&

		    kernel_supports(FEAT_PROG_BIND_MAP)) {

			struct bpf_map *rodata_map =

				&prog->obj->maps[prog->obj->rodata_map_idx];



			if (bpf_prog_bind_map(ret, bpf_map__fd(rodata_map), NULL)) {

				cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));

				pr_warn("prog '%s': failed to bind .rodata map: %s\n",

					prog->name, cp);

				/* Don't fail hard if can't bind rodata. */

			}

		}



		*pfd = ret;

		ret = 0;

		goto out;

tools/lib/bpf/libbpf.map

+1 −0
Original line number Diff line number Diff line
@@ -302,6 +302,7 @@ LIBBPF_0.1.0 { 


LIBBPF_0.2.0 {

	global:

		bpf_prog_bind_map;

		bpf_program__section_name;

		perf_buffer__buffer_cnt;

		perf_buffer__buffer_fd;