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

[Tiezhu Yang]

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@xxxxxxxxxxx/

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

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