linux-kernel - Re: [PATCH bpf-next 01/11] bpf: Move insn if/else into do_check

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <874izus6ok.fsf@fau.de>
Date: Sat, 15 Mar 2025 15:35:23 +0100
From: Luis Gerhorst <luis.gerhorst@....de>
To: Eduard Zingerman <eddyz87@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>,  Daniel Borkmann
 <daniel@...earbox.net>,  Andrii Nakryiko <andrii@...nel.org>,  Martin
 KaFai Lau <martin.lau@...ux.dev>,  Song Liu <song@...nel.org>,  Yonghong
 Song <yonghong.song@...ux.dev>,  John Fastabend
 <john.fastabend@...il.com>,  KP Singh <kpsingh@...nel.org>,  Stanislav
 Fomichev <sdf@...ichev.me>,  Hao Luo <haoluo@...gle.com>,  Jiri Olsa
 <jolsa@...nel.org>,  Puranjay Mohan <puranjay@...nel.org>,  Xu Kuohai
 <xukuohai@...weicloud.com>,  Catalin Marinas <catalin.marinas@....com>,
  Will Deacon <will@...nel.org>,  Hari Bathini <hbathini@...ux.ibm.com>,
  Christophe Leroy <christophe.leroy@...roup.eu>,  Naveen N Rao
 <naveen@...nel.org>,  Madhavan Srinivasan <maddy@...ux.ibm.com>,  Michael
 Ellerman <mpe@...erman.id.au>,  Nicholas Piggin <npiggin@...il.com>,
  Mykola Lysenko <mykolal@...com>,  Shuah Khan <shuah@...nel.org>,
  Henriette Herzog <henriette.herzog@....de>,  Cupertino Miranda
 <cupertino.miranda@...cle.com>,  Matan Shachnai <m.shachnai@...il.com>,
  Dimitar Kanaliev <dimitar.kanaliev@...eground.com>,  Shung-Hsi Yu
 <shung-hsi.yu@...e.com>,  Daniel Xu <dxu@...uu.xyz>,  bpf@...r.kernel.org,
  linux-arm-kernel@...ts.infradead.org,  linux-kernel@...r.kernel.org,
  linuxppc-dev@...ts.ozlabs.org,  linux-kselftest@...r.kernel.org,  George
 Guo <guodongtai@...inos.cn>,  WANG Xuerui <git@...0n.name>,  Tiezhu Yang
 <yangtiezhu@...ngson.cn>,  Maximilian Ott <ott@...fau.de>,  Milan Stephan
 <milan.stephan@....de>
Subject: Re: [PATCH bpf-next 01/11] bpf: Move insn if/else into do_check_insn()

Eduard Zingerman <eddyz87@...il.com> writes:
> On Thu, 2025-03-13 at 18:21 +0100, Luis Gerhorst wrote:
>> +		err = do_check_insn(env, insn, pop_log, &do_print_state, regs, state,
>> +				    &prev_insn_idx);
>
> - `regs` remains declared in do_check(), while nothing prevents
>   pushing its declaration to do_check_insn().
> - `state` is `env->cur_state`, so I'd avoid passing it as a parameter
>   (just to reduce count);
> - `prev_insn_idx` is unused by `do_check_insn`;
> - `pop_log` is not used by `do_check_insn`;

Changed for v2, thank you very much.

> - given that `insn` is presumed to correspond to `env->insn_idx` in
>   many places down the stack not sure about this parameter.

I don't have a strong opinion on this either. Unless someone objects I
will keep it as it matches the other check_*() functions like this.

>> +		if (err < 0) {
>> +			return err;
>> +		} else if (err == INSN_IDX_MODIFIED) {
>
> Also, I'd get rid of `INSN_IDX_MODIFIED` and move `env->insn_idx++`
> into `do_check_insn()`. This would save a few mental cycles when
> looking at the code with full patch-set applied:
>
> 		} else if (err == INSN_IDX_MODIFIED) {
> 			continue;
> 		} else if (err == PROCESS_BPF_EXIT) {
> 			goto process_bpf_exit;
> 		}
> 		WARN_ON_ONCE(err);
>
> 		if (state->speculative && cur_aux(env)->nospec_result) {
> 			... bunch of actions ...
> 		}
>
> 		env->insn_idx++;
>
> One needs to stop for a moment and think why "bunch of actions" is
> performed for regular index increment, but not for INSN_IDX_MODIFIED.

That certainly makes it more readable. I changed it for v2.

If we have an instruction that does not simply do `insn_idx++` but
jumps, the `nospec_result` check should never trigger. Otherwise, the
patched nospec might be skipped. Currently, this is satisfied because
`nospec_result` is only used for store-instructions. I will add a
comment and WARN_ON_ONCE to document that for v2.