Commit 9dbe6015 authored by Kumar Kartikeya Dwivedi's avatar Kumar Kartikeya Dwivedi Committed by Alexei Starovoitov
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libbpf: Support kernel module function calls 



This patch adds libbpf support for kernel module function call support.
The fd_array parameter is used during BPF program load to pass module
BTFs referenced by the program. insn->off is set to index into this
array, but starts from 1, because insn->off as 0 is reserved for
btf_vmlinux.

We try to use existing insn->off for a module, since the kernel limits
the maximum distinct module BTFs for kfuncs to 256, and also because
index must never exceed the maximum allowed value that can fit in
insn->off (INT16_MAX). In the future, if kernel interprets signed offset
as unsigned for kfunc calls, this limit can be increased to UINT16_MAX.

Also introduce a btf__find_by_name_kind_own helper to start searching
from module BTF's start id when we know that the BTF ID is not present
in vmlinux BTF (in find_ksym_btf_id).

Signed-off-by: default avatarKumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211002011757.311265-7-memxor@gmail.com
parent 0e32dfc8

tools/lib/bpf/bpf.c

+1 −0
Original line number Diff line number Diff line
@@ -264,6 +264,7 @@ int libbpf__bpf_prog_load(const struct bpf_prog_load_params *load_attr) 
	attr.line_info_rec_size = load_attr->line_info_rec_size;

	attr.line_info_cnt = load_attr->line_info_cnt;

	attr.line_info = ptr_to_u64(load_attr->line_info);

	attr.fd_array = ptr_to_u64(load_attr->fd_array);



	if (load_attr->name)

		memcpy(attr.prog_name, load_attr->name,

tools/lib/bpf/btf.c

+15 −3
Original line number Diff line number Diff line
@@ -695,15 +695,15 @@ __s32 btf__find_by_name(const struct btf *btf, const char *type_name) 
	return libbpf_err(-ENOENT);

}



__s32 btf__find_by_name_kind(const struct btf *btf, const char *type_name,

			     __u32 kind)

static __s32 btf_find_by_name_kind(const struct btf *btf, int start_id,

				   const char *type_name, __u32 kind)

{

	__u32 i, nr_types = btf__get_nr_types(btf);



	if (kind == BTF_KIND_UNKN || !strcmp(type_name, "void"))

		return 0;



	for (i = 1; i <= nr_types; i++) {

	for (i = start_id; i <= nr_types; i++) {

		const struct btf_type *t = btf__type_by_id(btf, i);

		const char *name;
@@ -717,6 +717,18 @@ __s32 btf__find_by_name_kind(const struct btf *btf, const char *type_name, 
	return libbpf_err(-ENOENT);

}



__s32 btf__find_by_name_kind_own(const struct btf *btf, const char *type_name,

				 __u32 kind)

{

	return btf_find_by_name_kind(btf, btf->start_id, type_name, kind);

}



__s32 btf__find_by_name_kind(const struct btf *btf, const char *type_name,

			     __u32 kind)

{

	return btf_find_by_name_kind(btf, 1, type_name, kind);

}



static bool btf_is_modifiable(const struct btf *btf)

{

	return (void *)btf->hdr != btf->raw_data;

tools/lib/bpf/libbpf.c

+53 −21
Original line number Diff line number Diff line
@@ -443,6 +443,11 @@ struct extern_desc { 


			/* local btf_id of the ksym extern's type. */

			__u32 type_id;

			/* BTF fd index to be patched in for insn->off, this is

			 * 0 for vmlinux BTF, index in obj->fd_array for module

			 * BTF

			 */

			__s16 btf_fd_idx;

		} ksym;

	};

};
@@ -454,6 +459,7 @@ struct module_btf { 
	char *name;

	__u32 id;

	int fd;

	int fd_array_idx;

};



struct bpf_object {
@@ -539,6 +545,10 @@ struct bpf_object { 
	void *priv;

	bpf_object_clear_priv_t clear_priv;



	int *fd_array;

	size_t fd_array_cap;

	size_t fd_array_cnt;



	char path[];

};

#define obj_elf_valid(o)	((o)->efile.elf)
@@ -5407,6 +5417,7 @@ bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog) 
			ext = &obj->externs[relo->sym_off];

			insn[0].src_reg = BPF_PSEUDO_KFUNC_CALL;

			insn[0].imm = ext->ksym.kernel_btf_id;

			insn[0].off = ext->ksym.btf_fd_idx;

			break;

		case RELO_SUBPROG_ADDR:

			if (insn[0].src_reg != BPF_PSEUDO_FUNC) {
@@ -6236,6 +6247,7 @@ load_program(struct bpf_program *prog, struct bpf_insn *insns, int insns_cnt, 
	}

	load_attr.log_level = prog->log_level;

	load_attr.prog_flags = prog->prog_flags;

	load_attr.fd_array = prog->obj->fd_array;



	/* adjust load_attr if sec_def provides custom preload callback */

	if (prog->sec_def && prog->sec_def->preload_fn) {
@@ -6752,13 +6764,14 @@ static int bpf_object__read_kallsyms_file(struct bpf_object *obj) 


static int find_ksym_btf_id(struct bpf_object *obj, const char *ksym_name,

			    __u16 kind, struct btf **res_btf,

			    int *res_btf_fd)

			    struct module_btf **res_mod_btf)

{

	int i, id, btf_fd, err;

	struct module_btf *mod_btf;

	struct btf *btf;

	int i, id, err;



	btf = obj->btf_vmlinux;

	btf_fd = 0;

	mod_btf = NULL;

	id = btf__find_by_name_kind(btf, ksym_name, kind);



	if (id == -ENOENT) {
@@ -6767,10 +6780,10 @@ static int find_ksym_btf_id(struct bpf_object *obj, const char *ksym_name, 
			return err;



		for (i = 0; i < obj->btf_module_cnt; i++) {

			btf = obj->btf_modules[i].btf;

			/* we assume module BTF FD is always >0 */

			btf_fd = obj->btf_modules[i].fd;

			id = btf__find_by_name_kind(btf, ksym_name, kind);

			/* we assume module_btf's BTF FD is always >0 */

			mod_btf = &obj->btf_modules[i];

			btf = mod_btf->btf;

			id = btf__find_by_name_kind_own(btf, ksym_name, kind);

			if (id != -ENOENT)

				break;

		}
@@ -6779,7 +6792,7 @@ static int find_ksym_btf_id(struct bpf_object *obj, const char *ksym_name, 
		return -ESRCH;



	*res_btf = btf;

	*res_btf_fd = btf_fd;

	*res_mod_btf = mod_btf;

	return id;

}
@@ -6788,11 +6801,12 @@ static int bpf_object__resolve_ksym_var_btf_id(struct bpf_object *obj, 
{

	const struct btf_type *targ_var, *targ_type;

	__u32 targ_type_id, local_type_id;

	struct module_btf *mod_btf = NULL;

	const char *targ_var_name;

	int id, btf_fd = 0, err;

	struct btf *btf = NULL;

	int id, err;



	id = find_ksym_btf_id(obj, ext->name, BTF_KIND_VAR, &btf, &btf_fd);

	id = find_ksym_btf_id(obj, ext->name, BTF_KIND_VAR, &btf, &mod_btf);

	if (id == -ESRCH && ext->is_weak) {

		return 0;

	} else if (id < 0) {
@@ -6827,7 +6841,7 @@ static int bpf_object__resolve_ksym_var_btf_id(struct bpf_object *obj, 
	}



	ext->is_set = true;

	ext->ksym.kernel_btf_obj_fd = btf_fd;

	ext->ksym.kernel_btf_obj_fd = mod_btf ? mod_btf->fd : 0;

	ext->ksym.kernel_btf_id = id;

	pr_debug("extern (var ksym) '%s': resolved to [%d] %s %s\n",

		 ext->name, id, btf_kind_str(targ_var), targ_var_name);
@@ -6839,26 +6853,20 @@ static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj, 
						struct extern_desc *ext)

{

	int local_func_proto_id, kfunc_proto_id, kfunc_id;

	struct module_btf *mod_btf = NULL;

	const struct btf_type *kern_func;

	struct btf *kern_btf = NULL;

	int ret, kern_btf_fd = 0;

	int ret;



	local_func_proto_id = ext->ksym.type_id;



	kfunc_id = find_ksym_btf_id(obj, ext->name, BTF_KIND_FUNC,

				    &kern_btf, &kern_btf_fd);

	kfunc_id = find_ksym_btf_id(obj, ext->name, BTF_KIND_FUNC, &kern_btf, &mod_btf);

	if (kfunc_id < 0) {

		pr_warn("extern (func ksym) '%s': not found in kernel BTF\n",

			ext->name);

		return kfunc_id;

	}



	if (kern_btf != obj->btf_vmlinux) {

		pr_warn("extern (func ksym) '%s': function in kernel module is not supported\n",

			ext->name);

		return -ENOTSUP;

	}



	kern_func = btf__type_by_id(kern_btf, kfunc_id);

	kfunc_proto_id = kern_func->type;
@@ -6870,9 +6878,30 @@ static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj, 
		return -EINVAL;

	}



	/* set index for module BTF fd in fd_array, if unset */

	if (mod_btf && !mod_btf->fd_array_idx) {

		/* insn->off is s16 */

		if (obj->fd_array_cnt == INT16_MAX) {

			pr_warn("extern (func ksym) '%s': module BTF fd index %d too big to fit in bpf_insn offset\n",

				ext->name, mod_btf->fd_array_idx);

			return -E2BIG;

		}

		/* Cannot use index 0 for module BTF fd */

		if (!obj->fd_array_cnt)

			obj->fd_array_cnt = 1;



		ret = libbpf_ensure_mem((void **)&obj->fd_array, &obj->fd_array_cap, sizeof(int),

					obj->fd_array_cnt + 1);

		if (ret)

			return ret;

		mod_btf->fd_array_idx = obj->fd_array_cnt;

		/* we assume module BTF FD is always >0 */

		obj->fd_array[obj->fd_array_cnt++] = mod_btf->fd;

	}



	ext->is_set = true;

	ext->ksym.kernel_btf_obj_fd = kern_btf_fd;

	ext->ksym.kernel_btf_id = kfunc_id;

	ext->ksym.btf_fd_idx = mod_btf ? mod_btf->fd_array_idx : 0;

	pr_debug("extern (func ksym) '%s': resolved to kernel [%d]\n",

		 ext->name, kfunc_id);
@@ -7031,6 +7060,9 @@ int bpf_object__load_xattr(struct bpf_object_load_attr *attr) 
			err = bpf_gen__finish(obj->gen_loader);

	}



	/* clean up fd_array */

	zfree(&obj->fd_array);



	/* clean up module BTFs */

	for (i = 0; i < obj->btf_module_cnt; i++) {

		close(obj->btf_modules[i].fd);

tools/lib/bpf/libbpf_internal.h

+3 −0
Original line number Diff line number Diff line
@@ -298,6 +298,7 @@ struct bpf_prog_load_params { 
	__u32 log_level;

	char *log_buf;

	size_t log_buf_sz;

	int *fd_array;

};



int libbpf__bpf_prog_load(const struct bpf_prog_load_params *load_attr);
@@ -408,6 +409,8 @@ int btf_type_visit_type_ids(struct btf_type *t, type_id_visit_fn visit, void *ct 
int btf_type_visit_str_offs(struct btf_type *t, str_off_visit_fn visit, void *ctx);

int btf_ext_visit_type_ids(struct btf_ext *btf_ext, type_id_visit_fn visit, void *ctx);

int btf_ext_visit_str_offs(struct btf_ext *btf_ext, str_off_visit_fn visit, void *ctx);

__s32 btf__find_by_name_kind_own(const struct btf *btf, const char *type_name,

				 __u32 kind);



extern enum libbpf_strict_mode libbpf_mode;