Re: [RFC PATCH bpf 1/6] bpf: Disallow interpreter fallback for user BPF_ADDR_SPACE_CAST insn

[Tiezhu Yang <yangtiezhu@loongson.cn>]

On 2026/6/30 下午10:36, Leon Hwang wrote:
> On 2026/6/30 22:29, KaFai Wan wrote:
>> On Fri, 2026-06-26 at 23:43 +0800, Leon Hwang wrote:
> [...]
>>>   /* Fix up helper call offsets on JIT fallback path. */
>>> -static void bpf_fixup_fallback_helpers(struct bpf_verifier_env *env, struct bpf_prog *fp)
>>> +static int bpf_fixup_fallback_helpers(struct bpf_verifier_env *env, struct bpf_prog *fp)
>>>   {
>>>   	struct bpf_insn *insn = fp->insnsi;
>>>   	const struct bpf_func_proto *fn;
>>>   	int i;
>>>   
>>> -	if (!env || !env->ops->get_func_proto)
>>> -		return;
>>> +	if (!env)
>>> +		return 0;
>>>   
>>>   	for (i = 0; i < fp->len; i++, insn++) {
>>> -		if (bpf_helper_call(insn) && bpf_jit_inlines_helper_call(insn->imm)) {
>>> +		if (env->ops->get_func_proto && bpf_helper_call(insn) &&
>>> +		    bpf_jit_inlines_helper_call(insn->imm)) {
>>>   			fn = env->ops->get_func_proto(insn->imm, env->prog);
>>>   			if (fn && fn->func)
>>>   				insn->imm = fn->func - __bpf_call_base;
>> It might be better to use the BPF_CALL_IMM macro. insn->imm = BPF_CALL_IMM(fn->func);
> 
> 
> Makes sense.
> 
> This might be applied to Tiezhu's patch.

Hi all,

Alexei said in another thread like this:

```
 > [3] 
https://lore.kernel.org/bpf/20260615025316.24429-1-yangtiezhu@loongson.cn/

I don't think we need such fallback in patch [3].
```
https://lore.kernel.org/bpf/DJMRIZ5PDWP4.12OOZ8H881H6O@gmail.com/

Should I just drop my previous patch? To be honest, I'm not sure how to 
solve the issue mentioned in it. Is that a real problem, and does it 
need to be fixed? What is the next step?

Thanks,
Tiezhu