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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: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211002011757.311265-7-memxor@gmail.com
This commit is contained in:
Kumar Kartikeya Dwivedi 2021-10-02 06:47:54 +05:30 committed by Alexei Starovoitov
parent 0e32dfc80b
commit 9dbe601563
4 changed files with 72 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
tools/lib/bpf/bpf.c
View File

@ -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,

18
tools/lib/bpf/btf.c
View File

@ -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;

74
tools/lib/bpf/libbpf.c
View File

@ -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 @@ out:
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);

3
tools/lib/bpf/libbpf_internal.h
View File

@ -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;