linux-kernel - Re: [PATCH 1/2] bpf: Remove struct bpf_verifier_env argument from print_bpf

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Date:   Wed, 21 Mar 2018 17:25:33 +0000
From:   Quentin Monnet <quentin.monnet@...ronome.com>
To:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     lkml <linux-kernel@...r.kernel.org>, netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] bpf: Remove struct bpf_verifier_env argument from
 print_bpf_insn

2018-03-21 16:02 UTC+0100 ~ Jiri Olsa <jolsa@...nel.org>
> We use print_bpf_insn in user space (bpftool and soon perf),
> so it'd be nice to keep it generic and strip it off the kernel
> struct bpf_verifier_env argument.
> 
> This argument can be safely removed, because its users can
> use the struct bpf_insn_cbs::private_data to pass it.
> 
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  kernel/bpf/disasm.c   | 52 +++++++++++++++++++++++++--------------------------
>  kernel/bpf/disasm.h   |  5 +----
>  kernel/bpf/verifier.c |  6 +++---
>  3 files changed, 30 insertions(+), 33 deletions(-)
> 

[...]

> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index c6eff108aa99..9f27d3fa7259 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -202,8 +202,7 @@ EXPORT_SYMBOL_GPL(bpf_verifier_log_write);
>   * generic for symbol export. The function was renamed, but not the calls in
>   * the verifier to avoid complicating backports. Hence the alias below.
>   */
> -static __printf(2, 3) void verbose(struct bpf_verifier_env *env,
> -				   const char *fmt, ...)
> +static __printf(2, 3) void verbose(void *private_data, const char *fmt, ...)
>  	__attribute__((alias("bpf_verifier_log_write")));

Just as a note, verbose() will be aliased to a function whose prototype
differs (bpf_verifier_log_write() still expects a struct
bpf_verifier_env as its first argument). I am not so familiar with
function aliases, could this change be a concern?

Other than this the patch seems good to me.
Quentin

>  
>  static bool type_is_pkt_pointer(enum bpf_reg_type type)
> @@ -4601,10 +4600,11 @@ static int do_check(struct bpf_verifier_env *env)
>  		if (env->log.level) {
>  			const struct bpf_insn_cbs cbs = {
>  				.cb_print	= verbose,
> +				.private_data	= env,
>  			};
>  
>  			verbose(env, "%d: ", insn_idx);
> -			print_bpf_insn(&cbs, env, insn, env->allow_ptr_leaks);
> +			print_bpf_insn(&cbs, insn, env->allow_ptr_leaks);
>  		}
>  
>  		if (bpf_prog_is_dev_bound(env->prog->aux)) {
>