From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 96C44C4338F for ; Wed, 18 Aug 2021 09:35:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7F8DE60551 for ; Wed, 18 Aug 2021 09:35:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233145AbhHRJfS (ORCPT ); Wed, 18 Aug 2021 05:35:18 -0400 Received: from mail-lj1-f173.google.com ([209.85.208.173]:35707 "EHLO mail-lj1-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233729AbhHRJe2 (ORCPT ); Wed, 18 Aug 2021 05:34:28 -0400 Received: by mail-lj1-f173.google.com with SMTP id y6so3964461lje.2; Wed, 18 Aug 2021 02:33:51 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=CzC7eMg6GoorXihbZpnBiMn0rer4lRtJPAUz1wNS7Ds=; b=DLZXoPf7Dv9d35O+flm97fCaasEQnPwFPFtSRBSvjLOsvq5Xixo7UkXN/U09L/Htaq QEXQQ38ScqBKZDJ5wH2iCa9yGbeCiKj4H3Ls6vwIKKPTfeAK/uZMb/gEJgxtPK3UQukP txvFkcsI2/rQNRKouXjwUNrtPRZZR5ISjKZ637+FQl/1vj5buwDFQlSY1xMLtp9ar8xN 6myV1g4EWi4zDuYv8RJuOrlZcr4wA1ji4mR8W70L6dw2Dh2LOzITt7F2XgA6MMYWMjkm JKYKFU8HH9VBf7QobF7QvMtMCm8pcLlym9r/noUYVVeg+Liy1fFq9+kAFMxe+Akfn1sV 9N/A== X-Gm-Message-State: AOAM532CQi+7UVwEX2cfdxrqMI+OVOTLYg6ZPijsrgIV7dat5kd+F/jA b10xeC9LuUnmO4pIB/Iu3RW2WhyQBqOh0OVnfi4= X-Google-Smtp-Source: ABdhPJwHqkci/wVHZz1RIQo9bHJpWPoiaE+GXkLl0fV34qDOm85KGMeIPwC/RwTgPkoYJWCGg83a0bkp1B1FDN32yQQ= X-Received: by 2002:a2e:a288:: with SMTP id k8mr6989386lja.315.1629279230564; Wed, 18 Aug 2021 02:33:50 -0700 (PDT) MIME-Version: 1.0 References: <20210818034010.800652-1-keescook@chromium.org> <202108172320.1540EC10C@keescook> <202108180159.5C1CEE70F@keescook> In-Reply-To: <202108180159.5C1CEE70F@keescook> From: Vincent MAILHOL Date: Wed, 18 Aug 2021 18:33:39 +0900 Message-ID: Subject: Re: [PATCH] can: etas_es58x: Replace 0-element raw_msg array To: Kees Cook Cc: Wolfgang Grandegger , Marc Kleine-Budde , "David S. Miller" , Jakub Kicinski , Arunachalam Santhanam , linux-can , netdev , open list , linux-hardening@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-can@vger.kernel.org On Wed. 18 Aug 2021 at 18:03, Kees Cook wrote: > On Wed, Aug 18, 2021 at 04:55:20PM +0900, Vincent MAILHOL wrote: > > At the end, the only goal of raw_msg[] is to have a tag pointing > > to the beginning of the union. It would be virtually identical to > > something like: > > | u8 raw_msg[]; > > | union { > > | /* ... */ > > | } __packed ; > > > > I had a look at your work and especially at your struct_group() macro. > > Do you think it would make sense to introduce a union_group()? > > > > Result would look like: > > > > | union_group_attr(urb_msg, __packed, /* raw_msg renamed to urb_msg */ > > | struct es58x_fd_tx_conf_msg tx_conf_msg; > > | u8 tx_can_msg_buf[ES58X_FD_TX_BULK_MAX * ES58X_FD_CANFD_TX_LEN]; > > | u8 rx_can_msg_buf[ES58X_FD_RX_BULK_MAX * ES58X_FD_CANFD_RX_LEN]; > > | struct es58x_fd_echo_msg echo_msg[ES58X_FD_ECHO_BULK_MAX]; > > | struct es58x_fd_rx_event_msg rx_event_msg; > > | struct es58x_fd_tx_ack_msg tx_ack_msg; > > | __le64 timestamp; > > | __le32 rx_cmd_ret_le32; > > | ); > > > > And I can then use urb_msg in place of the old raw_msg (might > > need a bit of rework here and there but I can take care of it). > > > > This is the most pretty way I can think of to remove this zero length array. > > Keeping the raw_msg[] but with another size seems odd to me. > > > > Or maybe I would be the only one using this feature in the full > > tree? In that case, maybe it would make sense to keep the > > union_group_attr() macro local to the etas_es58x driver? > > I actually ended up with something close to this idea, but more > generalized for other cases in the kernel. There was a sane way to > include a "real" flexible array in a union (or alone in a struct), so > I've proposed this flex_array() helper: > https://lore.kernel.org/lkml/20210818081118.1667663-2-keescook@chromium.org/ > > and then it's just a drop-in replacement for all the places that need > this fixed, including etas_es58x: > https://lore.kernel.org/lkml/20210818081118.1667663-3-keescook@chromium.org/#Z30drivers:net:can:usb:etas_es58x:es581_4.h > > Hopefully this will work out; I think it's as clean as we can get for > now. :) The __flex_array itself is a nasty hack :D but the rest is clean. Is this compliant to the C standard? Well, I guess that as long as both GCC and LLVM supports it, it is safe to add it to the kernel. I like the final result. I will do a bit more testing and give my acknowledgement if everything goes well. Yours sincerely, Vincent