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

[Song Chen <chensong_2000@126.com>]

Hi,

On 5/12/26 11:56, Kaitao Cheng wrote:
> 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.
> 

you mean "git send-email 0001-*.patch 0002-*.patch 0003-*.patch", i 
didn't know that before, thanks so much.

>> 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.

Many thanks, i did checkpatch every time, but i probably forgot it this 
time, sorry about that. As the reviews' comments, looks like this patch 
has its shot, more attention will be paid on v3.

> 
>> +		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);
> 

will do.

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


best regards,

Song