Re: [PATCH bpf-next 1/2] bpf: Print breakdown of insns processed by subprogs

["Kumar Kartikeya Dwivedi" <memxor@gmail.com>]

On Wed Apr 29, 2026 at 1:08 AM CEST, sashiko-bot wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] Out-of-bounds read in `bpf_subprog_is_global()` when printing verification stats for programs with hidden subprograms.
> --
>
> commit 08128f883e58301e0f97b1d4a94656be63b8f790
> Author: Paul Chaignon <paul.chaignon@gmail.com>
>
> bpf: Print breakdown of insns processed by subprogs
>
> This patch tracks the number of instructions processed by each global
> function (subprog) during BPF verification. It then reports this
> breakdown in the verifier logs under BPF_LOG_STATS.
>
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>> index 03f9e16c2abe..b48389b48eb6 100644
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>
> [ ... ]
>
>> @@ -18288,6 +18295,13 @@ static void print_verification_stats(struct bpf_verifier_env *env)
>>  				verbose(env, "+");
>>  		}
>>  		verbose(env, "\n");
>> +		verbose(env, "insns processed %d", env->subprog_info[0].insn_processed);
>> +		for (i = 1; i < env->subprog_cnt; i++) {
>> +			if (!bpf_subprog_is_global(env, i))
>
> Could this introduce a regression due to an out-of-bounds read on the
> func_info_aux array if there are hidden subprograms?
>
> At load time, if BTF is present, env->prog->aux->func_info_aux is allocated
> with exactly func_info_cnt elements, and env->subprog_cnt initially matches
> func_info_cnt.
>
> During verification, if a feature like bpf_throw is used without an explicit
> callback, add_hidden_subprog() is called which increments env->subprog_cnt
> but does not resize the func_info_aux array.
>
> Since this loop iterates up to the updated env->subprog_cnt, when i reaches
> the index of a hidden subprogram, bpf_subprog_is_global() will access
> aux[i].linkage where i >= func_info_cnt:
>
> kernel/bpf/verifier.c:bpf_subprog_is_global() {
> 	struct bpf_func_info_aux *aux = env->prog->aux->func_info_aux;
>
> 	return aux && aux[subprog].linkage == BTF_FUNC_GLOBAL;
> }
>
> Is it possible to skip hidden subprograms here, or limit the check to
> func_info_cnt?

Don't see it happening, since hidden subprogs never get verified, so we won't
invoke bpf_subprog_is_global() with such a subprog index.