Re: [PATCH bpf-next v7 1/2] bpf: Introduce jit_required flag and refactor kfunc path

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The `bpf_fixup_call_args()` function and `bpf_prog_has_kfunc_call()` macro were not updated to use the new `jit_required` flag, leading to inconsistent interpreter fallback behavior for pruned kfuncs.
--

commit 5a3f8861c2b6916fe194f97a407cb7265f545fd0
Author: Tiezhu Yang <yangtiezhu@loongson.cn>

bpf: Introduce jit_required flag and refactor kfunc path

Introduce a 'jit_required' bitfield flag at the end of the
flags group in struct bpf_prog. This bit tracks whether a
program strictly requires the JIT compiler.

> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 649cce41e13f3..5fcd19ccb41a9 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -2619,8 +2619,7 @@ struct bpf_prog *__bpf_prog_select_runtime(struct bpf_verifier_env *env, struct
>  	if (fp->bpf_func)
>  		goto finalize;
>  
> -	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) ||
> -	    bpf_prog_has_kfunc_call(fp))
> +	if (IS_ENABLED(CONFIG_BPF_JIT_ALWAYS_ON) || fp->jit_required)
>  		jit_needed = true;
>  
>  	if (!bpf_prog_select_interpreter(fp))

[Severity: Medium]
Since bpf_prog_has_kfunc_call() was replaced here with fp->jit_required,
should bpf_fixup_call_args() in kernel/bpf/fixups.c also be updated to use
the new flag?

Currently, bpf_fixup_call_args() still calls bpf_prog_has_kfunc_call(). If
a program has a pruned kfunc (allocating kfunc_tab but leaving
jit_required=0) and JIT falls back to the interpreter, wouldn't
bpf_fixup_call_args() incorrectly reject the program with -EINVAL?

kernel/bpf/fixups.c:bpf_fixup_call_args() {
    ...
	bool has_kfunc_call = bpf_prog_has_kfunc_call(prog);
    ...
	if (has_kfunc_call) {
		verbose(env, "calling kernel functions are not allowed in non-JITed programs\n");
		return -EINVAL;
	}
    ...
}

Should bpf_prog_has_kfunc_call() in kernel/bpf/verifier.c be updated to
check prog->jit_required, or removed entirely in favor of checking the flag
directly?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260702143656.28845-1-yangtiezhu@loongson.cn?part=1