netdev - Re: [RFC PATCH v3 bpf-next 2/5] bpf/verifier: rewrite subprog boundary detection

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Message-ID: <20180417234826.egydr2sg2rewzvyu@ast-mbp>
Date:   Tue, 17 Apr 2018 16:48:27 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Edward Cree <ecree@...arflare.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org
Subject: Re: [RFC PATCH v3 bpf-next 2/5] bpf/verifier: rewrite subprog
 boundary detection

On Fri, Apr 06, 2018 at 06:13:59PM +0100, Edward Cree wrote:
> By storing a subprogno in each insn's aux data, we avoid the need to keep
>  the list of subprog starts sorted or bsearch() it in find_subprog().
> Also, get rid of the weird one-based indexing of subprog numbers.
> 
> Signed-off-by: Edward Cree <ecree@...arflare.com>
> ---
>  include/linux/bpf_verifier.h |   3 +-
>  kernel/bpf/verifier.c        | 284 ++++++++++++++++++++++++++-----------------
>  2 files changed, 177 insertions(+), 110 deletions(-)
> 
> diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> index 8f70dc181e23..17990dd56e65 100644
> --- a/include/linux/bpf_verifier.h
> +++ b/include/linux/bpf_verifier.h
> @@ -146,6 +146,7 @@ struct bpf_insn_aux_data {
>  		s32 call_imm;			/* saved imm field of call insn */
>  	};
>  	int ctx_field_size; /* the ctx field size for load insn, maybe 0 */
> +	u16 subprogno; /* subprog in which this insn resides */
>  	bool seen; /* this insn was processed by the verifier */
>  };

as I was saying before this is no go.
subprogno is meaningless in the hierarchy of: prog -> func -> bb -> insn
Soon bpf will have libraries and this field would need to become
a pointer back to bb or func structure creating unnecessary circular dependency.