[PATCH v5 bpf-next 1/8] bpf: factor out fetching basic kfunc metadata

Andrii Nakryiko
2023-03-08T18:41:32Z

Factor out logic to fetch basic kfunc metadata based on struct bpf_insn.
This is not exactly short or trivial code to just copy/paste and this
information is sometimes necessary in other parts of the verifier logic.
Subsequent patches will rely on this to determine if an instruction is
a kfunc call to iterator next method.

No functional changes intended, including that verbose() warning
behavior when kfunc is not allowed for a particular program type.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
kernel/bpf/verifier.c | 92 +++++++++++++++++++++++++++----------------
1 file changed, 59 insertions(+), 33 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index b2116ca78d9a..8d40fba6a1c0 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10079,24 +10079,21 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
return 0;
}

-static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
- int *insn_idx_p)
+static int fetch_kfunc_meta(struct bpf_verifier_env *env,
+ struct bpf_insn *insn,
+ struct bpf_kfunc_call_arg_meta *meta,
+ const char **kfunc_name)
{
- const struct btf_type *t, *func, *func_proto, *ptr_type;
- u32 i, nargs, func_id, ptr_type_id, release_ref_obj_id;
- struct bpf_reg_state *regs = cur_regs(env);
- const char *func_name, *ptr_type_name;
- bool sleepable, rcu_lock, rcu_unlock;
- struct bpf_kfunc_call_arg_meta meta;
- int err, insn_idx = *insn_idx_p;
- const struct btf_param *args;
- const struct btf_type *ret_t;
+ const struct btf_type *func, *func_proto;
+ u32 func_id, *kfunc_flags;
+ const char *func_name;
struct btf *desc_btf;
- u32 *kfunc_flags;

- /* skip for now, but return error when we find this in fixup_kfunc_call */
+ if (kfunc_name)
+ *kfunc_name = NULL;
+
if (!insn->imm)
- return 0;
+ return -EINVAL;

desc_btf = find_kfunc_desc_btf(env, insn->off);
if (IS_ERR(desc_btf))
@@ -10105,22 +10102,51 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
func_id = insn->imm;
func = btf_type_by_id(desc_btf, func_id);
func_name = btf_name_by_offset(desc_btf, func->name_off);
+ if (kfunc_name)
+ *kfunc_name = func_name;
func_proto = btf_type_by_id(desc_btf, func->type);

kfunc_flags = btf_kfunc_id_set_contains(desc_btf, resolve_prog_type(env->prog), func_id);
if (!kfunc_flags) {
- verbose(env, "calling kernel function %s is not allowed\n",
- func_name);
return -EACCES;
}

- /* Prepare kfunc call metadata */
- memset(&meta, 0, sizeof(meta));
- meta.btf = desc_btf;
- meta.func_id = func_id;
- meta.kfunc_flags = *kfunc_flags;
- meta.func_proto = func_proto;
- meta.func_name = func_name;
+ memset(meta, 0, sizeof(*meta));
+ meta->btf = desc_btf;
+ meta->func_id = func_id;
+ meta->kfunc_flags = *kfunc_flags;
+ meta->func_proto = func_proto;
+ meta->func_name = func_name;
+
+ return 0;
+}
+
+static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
+ int *insn_idx_p)
+{
+ const struct btf_type *t, *ptr_type;
+ u32 i, nargs, ptr_type_id, release_ref_obj_id;
+ struct bpf_reg_state *regs = cur_regs(env);
+ const char *func_name, *ptr_type_name;
+ bool sleepable, rcu_lock, rcu_unlock;
+ struct bpf_kfunc_call_arg_meta meta;
+ struct bpf_insn_aux_data *insn_aux;
+ int err, insn_idx = *insn_idx_p;
+ const struct btf_param *args;
+ const struct btf_type *ret_t;
+ struct btf *desc_btf;
+
+ /* skip for now, but return error when we find this in fixup_kfunc_call */
+ if (!insn->imm)
+ return 0;
+
+ err = fetch_kfunc_meta(env, insn, &meta, &func_name);
+ if (err == -EACCES && func_name)
+ verbose(env, "calling kernel function %s is not allowed\n", func_name);
+ if (err)
+ return err;
+ desc_btf = meta.btf;
+ insn_aux = &env->insn_aux_data[insn_idx];

if (is_kfunc_destructive(&meta) && !capable(CAP_SYS_BOOT)) {
verbose(env, "destructive kfunc calls require CAP_SYS_BOOT capability\n");
@@ -10173,7 +10199,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
err = release_reference(env, regs[meta.release_regno].ref_obj_id);
if (err) {
verbose(env, "kfunc %s#%d reference has not been acquired before\n",
- func_name, func_id);
+ func_name, meta.func_id);
return err;
}
}
@@ -10185,14 +10211,14 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
err = ref_convert_owning_non_owning(env, release_ref_obj_id);
if (err) {
verbose(env, "kfunc %s#%d conversion of owning ref to non-owning failed\n",
- func_name, func_id);
+ func_name, meta.func_id);
return err;
}

err = release_reference(env, release_ref_obj_id);
if (err) {
verbose(env, "kfunc %s#%d reference has not been acquired before\n",
- func_name, func_id);
+ func_name, meta.func_id);
return err;
}
}
@@ -10202,7 +10228,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
set_rbtree_add_callback_state);
if (err) {
verbose(env, "kfunc %s#%d failed callback verification\n",
- func_name, func_id);
+ func_name, meta.func_id);
return err;
}
}
@@ -10211,7 +10237,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
mark_reg_not_init(env, regs, caller_saved[i]);

/* Check return type */
- t = btf_type_skip_modifiers(desc_btf, func_proto->type, NULL);
+ t = btf_type_skip_modifiers(desc_btf, meta.func_proto->type, NULL);

if (is_kfunc_acquire(&meta) && !btf_type_is_struct_ptr(meta.btf, t)) {
/* Only exception is bpf_obj_new_impl */
@@ -10260,11 +10286,11 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
regs[BPF_REG_0].btf = ret_btf;
regs[BPF_REG_0].btf_id = ret_btf_id;

- env->insn_aux_data[insn_idx].obj_new_size = ret_t->size;
- env->insn_aux_data[insn_idx].kptr_struct_meta =
+ insn_aux->obj_new_size = ret_t->size;
+ insn_aux->kptr_struct_meta =
btf_find_struct_meta(ret_btf, ret_btf_id);
} else if (meta.func_id == special_kfunc_list[KF_bpf_obj_drop_impl]) {
- env->insn_aux_data[insn_idx].kptr_struct_meta =
+ insn_aux->kptr_struct_meta =
btf_find_struct_meta(meta.arg_obj_drop.btf,
meta.arg_obj_drop.btf_id);
} else if (meta.func_id == special_kfunc_list[KF_bpf_list_pop_front] ||
@@ -10397,8 +10423,8 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
regs[BPF_REG_0].id = ++env->id_gen;
} /* else { add_kfunc_call() ensures it is btf_type_is_void(t) } */

- nargs = btf_type_vlen(func_proto);
- args = (const struct btf_param *)(func_proto + 1);
+ nargs = btf_type_vlen(meta.func_proto);
+ args = (const struct btf_param *)(meta.func_proto + 1);
for (i = 0; i < nargs; i++) {
u32 regno = i + 1;

--
2.34.1