Enable module kfuncs to override vmlinux kfuncs

[kernel-patches-daemon-bpf]

Pull request for series with
subject: Enable module kfuncs to override vmlinux kfuncs
version: 1
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1087894

[kernel-patches-daemon-bpf]

Upstream branch: 9f5b3ff
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=1087894
version: 1

[kernel-patches-review-bot]

commit 8fbf08ef1da5223cb14bd1012a0a1057e40cb6fd
Author: Song Chen <chensong_2000@126.com>

kernel/bpf/verifier: Support module kfunc resolution via instruction offset

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.

> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 03f9e16c2abe..7e6a95e6821d 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -2734,7 +2734,10 @@ int bpf_add_kfunc_call(struct bpf_verifier_env *env, u32 func_id, u16 offset)
>  	if (err)
>  		return err;
>
> -	addr = kallsyms_lookup_name(kfunc.name);
> +	if (offset)
> +		addr = module_kallsyms_lookup_name(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;

When offset is non-zero, module_kallsyms_lookup_name(kfunc.name) searches
all loaded modules and returns the first match. How does this handle the
case where multiple modules register kfuncs with the same name?

In the original discussion thread from January 2026, Alexei Starovoitov
asked: "but what about kfunc in module A with the same name as kfunc in
module B?" You acknowledged this concern and indicated it was in your plan
to address. However, the current implementation appears to rely on module
load order when multiple modules have identically-named kfuncs.

Reference: https://lore.kernel.org/all/CAADnVQLVQW-Mb_d+zT+aSpPOZ042erPVcSHVBx9PMGET+a754Q@mail.gmail.com/

Is there a mechanism to ensure the correct module's kfunc is selected when
names collide across different modules?

---

AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

In-Reply-To-Subject: kernel/bpf/verifier: Support module kfunc resolution via instruction offset
CI run summary: https://github.com/kernel-patches/bpf/actions/runs/25150033548

[kernel-patches-daemon-bpf]

Forwarding comment 4350146673 via email
In-Reply-To: 20260430054714.38980-1-chensong_2000@126.com
Patch: https://patchwork.kernel.org/project/netdevbpf/patch/20260430054714.38980-1-chensong_2000@126.com/

[kernel-patches-daemon-bpf]

Upstream branch: 2ca6723
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=1087894
version: 1

[kernel-patches-daemon-bpf]

Upstream branch: 2ca6723
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=1087894
version: 1

[kernel-patches-daemon-bpf]

Upstream branch: 2ca6723
series: https://patchwork.kernel.org/project/netdevbpf/list/?series=1087894
version: 1