On 6/25/20 3:12 PM, Jiri Olsa wrote:
Now when we moved the helpers btf_id arrays into .BTF_ids section,
we can remove the code that resolve those IDs in runtime.
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
kernel/bpf/btf.c | 90 +++++-------------------------------------------
1 file changed, 8 insertions(+), 82 deletions(-)
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 4c3007f428b1..4da6b0770ff9 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -4079,96 +4079,22 @@ int btf_struct_access(struct bpf_verifier_log *log,
return -EINVAL;
}
-static int __btf_resolve_helper_id(struct bpf_verifier_log *log, void *fn,
- int arg)
+int btf_resolve_helper_id(struct bpf_verifier_log *log,
+ const struct bpf_func_proto *fn, int arg)
{
- char fnname[KSYM_SYMBOL_LEN + 4] = "btf_";
- const struct btf_param *args;
- const struct btf_type *t;
- const char *tname, *sym;
- u32 btf_id, i;
+ int id;
- if (IS_ERR(btf_vmlinux)) {
- bpf_log(log, "btf_vmlinux is malformed\n");
+ if (fn->arg_type[arg] != ARG_PTR_TO_BTF_ID)
return -EINVAL;
- }
-
- sym = kallsyms_lookup((long)fn, NULL, NULL, NULL, fnname + 4);
- if (!sym) {
- bpf_log(log, "kernel doesn't have kallsyms\n");
- return -EFAULT;
- }
- for (i = 1; i <= btf_vmlinux->nr_types; i++) {
- t = btf_type_by_id(btf_vmlinux, i);
- if (BTF_INFO_KIND(t->info) != BTF_KIND_TYPEDEF)
- continue;
- tname = __btf_name_by_offset(btf_vmlinux, t->name_off);
- if (!strcmp(tname, fnname))
- break;
- }
- if (i > btf_vmlinux->nr_types) {
- bpf_log(log, "helper %s type is not found\n", fnname);
- return -ENOENT;
- }
-
- t = btf_type_by_id(btf_vmlinux, t->type);
- if (!btf_type_is_ptr(t))
- return -EFAULT;
- t = btf_type_by_id(btf_vmlinux, t->type);
- if (!btf_type_is_func_proto(t))
- return -EFAULT;
-
- args = (const struct btf_param *)(t + 1);
- if (arg >= btf_type_vlen(t)) {
- bpf_log(log, "bpf helper %s doesn't have %d-th argument\n",
- fnname, arg);
+ if (WARN_ON_ONCE(!fn->btf_id))
The original code does not have this warning. It directly did
"ret = READ_ONCE(*btf_id);" after testing reg arg type ARG_PTR_TO_BTF_ID.
return -EINVAL;
- }
- t = btf_type_by_id(btf_vmlinux, args[arg].type);
- if (!btf_type_is_ptr(t) || !t->type) {
- /* anything but the pointer to struct is a helper config bug */
- bpf_log(log, "ARG_PTR_TO_BTF is misconfigured\n");
- return -EFAULT;
- }
- btf_id = t->type;
- t = btf_type_by_id(btf_vmlinux, t->type);
- /* skip modifiers */
- while (btf_type_is_modifier(t)) {
- btf_id = t->type;
- t = btf_type_by_id(btf_vmlinux, t->type);
- }
- if (!btf_type_is_struct(t)) {
- bpf_log(log, "ARG_PTR_TO_BTF is not a struct\n");
- return -EFAULT;
- }
- bpf_log(log, "helper %s arg%d has btf_id %d struct %s\n", fnname + 4,
- arg, btf_id, __btf_name_by_offset(btf_vmlinux, t->name_off));
- return btf_id;
-}
+ id = fn->btf_id[arg];
The corresponding BTF_ID definition here is:
BTF_ID_LIST(bpf_skb_output_btf_ids)
BTF_ID(struct, sk_buff)
The bpf helper writer needs to ensure proper declarations
of BTF_IDs like the above matching helpers definition.
Support we have arg1 and arg3 as BTF_ID. then the list
definition may be
BTF_ID_LIST(bpf_skb_output_btf_ids)
BTF_ID(struct, sk_buff)
BTF_ID(struct, __unused)
BTF_ID(struct, task_struct)
This probably okay, I guess.
-int btf_resolve_helper_id(struct bpf_verifier_log *log,
- const struct bpf_func_proto *fn, int arg)
-{
- int *btf_id = &fn->btf_id[arg];
- int ret;
-
- if (fn->arg_type[arg] != ARG_PTR_TO_BTF_ID)
+ if (!id || id > btf_vmlinux->nr_types)
return -EINVAL;
id == 0 if btf_id cannot be resolved by resolve_btfids, right?
when id may be greater than btf_vmlinux->nr_types? If resolve_btfids
application did incorrect transformation?
Anyway, this is to resolve helper meta btf_id. Even if you
return a btf_id > btf_vmlinux->nr_types, verifier will reject
since it will never be the same as the real parameter btf_id.
I would drop id > btf_vmlinux->nr_types here. This should never
happen for a correct tool. Even if it does, verifier will take
care of it.
-
- ret = READ_ONCE(*btf_id);
- if (ret)
- return ret;
- /* ok to race the search. The result is the same */
- ret = __btf_resolve_helper_id(log, fn->func, arg);
- if (!ret) {
- /* Function argument cannot be type 'void' */
- bpf_log(log, "BTF resolution bug\n");
- return -EFAULT;
- }
- WRITE_ONCE(*btf_id, ret);
- return ret;
+ return id;
}
static int __get_type_size(struct btf *btf, u32 btf_id,
