Re: [PATCH V2 2/2] kernel/bpf/verifier: Support module kfunc resolution via instruction offset

[Kaitao Cheng <kaitao.cheng@linux.dev>]

在 2026/5/10 11:01, Song Chen 写道:
> Use the instruction's 'off' field to indicate the source of a kfunc.
> When libbpf resolves a kfunc, it sets insn->off to 0 for vmlinux
> kfuncs or a non-zero module ID for module kfuncs.
> 
> The verifier now checks insn->off to determine where to look up the
> kfunc address: off == 0 searches in vmlinux, while off > 0 searches
> in the corresponding module BTF. This enables proper resolution of
> module kfuncs that may override vmlinux kfuncs with the same name.
> 
> This works in conjunction with the libbpf change that prioritizes
> module kfuncs during BTF resolution.
> 
> Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
> Signed-off-by: Song Chen <chensong_2000@126.com>
> 
> ---
> changelog:
> v1 --- v2:
> libbpf has already specified which module this kfunc belongs to as
> ebpf code onwer's expectation, then verifier uses
> find_kallsyms_symbol_value to search kfunc's addr.
> ---
>  kernel/bpf/verifier.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>  mode change 100644 => 100755 kernel/bpf/verifier.c

In general, the second and following parts of a multi-part patch should be
sent as a reply to the first part so that they all thread together at the
receiving end.  Tools like git and quilt have commands to mail out a set of
patches with the proper threading. 

> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> old mode 100644
> new mode 100755
> index 159b25f8269d..3b2e4552a3d4
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -3303,6 +3303,7 @@ static struct btf *__find_kfunc_desc_btf(struct bpf_verifier_env *env,
>  		 */
>  		sort(tab->descs, tab->nr_descs, sizeof(tab->descs[0]),
>  		     kfunc_btf_cmp_by_off, NULL);
> +

Unnecessary change.

>  	} else {
>  		btf = b->btf;
>  	}
> @@ -3498,7 +3499,16 @@ static int add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, s16 offset)
>  	if (err)
>  		return err;
>  
> -	addr = kallsyms_lookup_name(kfunc.name);
> +	if (offset) {
> +		struct bpf_kfunc_btf kf_btf = { .offset = offset };
> +		struct module *mod;
> +		struct bpf_kfunc_btf *b;
> +		b = bsearch(&kf_btf, btf_tab->descs, btf_tab->nr_descs,
> +            sizeof(btf_tab->descs[0]), kfunc_btf_cmp_by_off);

Tip: before submission, you can run scripts/checkpatch.pl to check for formatting issues.

> +		mod = b->module;
> +		addr = find_kallsyms_symbol_value(mod, kfunc.name);

struct bpf_kfunc_btf b, kf_btf = { .offset = offset };
    ......
addr = find_kallsyms_symbol_value(b->module, kfunc.name);

> +	} else
> +		addr = kallsyms_lookup_name(kfunc.name);
>  	if (!addr) {
>  		verbose(env, "cannot find address for kernel function %s\n", kfunc.name);
>  		return -EINVAL;

-- 
Thanks
Kaitao Cheng