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
diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 2401fad..7d1741c 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -264,6 +264,7 @@
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,
diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 6ad63e4..7774f99 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -695,15 +695,15 @@
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 @@
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;
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index e23f1b6..ea1c51d 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -443,6 +443,11 @@
/* 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 @@
char *name;
__u32 id;
int fd;
+ int fd_array_idx;
};
struct bpf_object {
@@ -539,6 +545,10 @@
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 @@
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_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 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 @@
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 @@
return -ESRCH;
*res_btf = btf;
- *res_btf_fd = btf_fd;
+ *res_mod_btf = mod_btf;
return id;
}
@@ -6788,11 +6801,12 @@
{
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 @@
}
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 @@
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 @@
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 @@
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);
diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index ec79400..f7fd394 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -298,6 +298,7 @@
__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_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;
