Re: [PATCH bpf-next v2 1/3] bpf: Report maximum combined stack depth

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] On early verifier failure, 'max_stack_depth' logs as 0, which is inconsistent with the individual subprog stack depths shown.
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commit 2f8f05d6e2f1d0777f2f9a6fc7f4f3d3c65baf3f
Author: Paul Chaignon <paul.chaignon@gmail.com>

bpf: Report maximum combined stack depth

This commit adds reporting for the maximum combined stack depth of BPF
programs to the verifier logs. It prints the max combined depth alongside
the per-subprog stack depths to provide a value closer to what is actually
enforced by the verifier.

> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 11054ad89c14d..39340a6780ebc 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
[ ... ]
> @@ -18289,7 +18293,7 @@ static void print_verification_stats(struct bpf_verifier_env *env)
>  		verbose(env, "stack depth %d", env->subprog_info[0].stack_depth);
>  		for (i = 1; i < subprog_cnt; i++)
>  			verbose(env, "+%d", env->subprog_info[i].stack_depth);
> -		verbose(env, "\n");
> +		verbose(env, " max %d\n", env->max_stack_depth);

If the verifier fails early during do_check_main() or do_check_subprogs(),
the process skips check_max_stack_depth() and jumps directly to the
cleanup and logging phase.

Since env->max_stack_depth is only calculated in check_max_stack_depth(),
could this result in confusing log output on early failures where the
subprog depths are printed with a max depth of 0?

For example, it might output something like:
stack depth 16+256 max 0

Would it be better to conditionally print this value only if the max stack
depth check actually ran, or otherwise indicate that the check was
bypassed?

>  		verbose(env, "insns processed %d", env->subprog_info[0].insn_processed);
>  		for (i = 1; i < subprog_cnt; i++)
>  			if (bpf_subprog_is_global(env, i))

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Sashiko AI review · https://sashiko.dev/#/patchset/cover.1778689025.git.paul.chaignon@gmail.com?part=1