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=-14.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=unavailable 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 A31BCC433DF for ; Thu, 4 Jun 2020 20:25:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 819852067B for ; Thu, 4 Jun 2020 20:25:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="eTUIYqIr" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729779AbgFDUZc (ORCPT ); Thu, 4 Jun 2020 16:25:32 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52224 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729806AbgFDUZa (ORCPT ); Thu, 4 Jun 2020 16:25:30 -0400 Received: from mail-pl1-x642.google.com (mail-pl1-x642.google.com [IPv6:2607:f8b0:4864:20::642]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 203B0C08C5C6 for ; Thu, 4 Jun 2020 13:25:29 -0700 (PDT) Received: by mail-pl1-x642.google.com with SMTP id bh7so2654809plb.11 for ; Thu, 04 Jun 2020 13:25:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=TblIMkzhKEVNZyPa1dQf8kFQ+MgYlpgsesY6pOK1xME=; b=eTUIYqIrq5sxbgWQO/3JauOnTYpVr1lxYINDt5nKOAMkJOKF9ufyGFqb5XSmsRi3m+ Uksx9+kJJ0xBVvvMTZtWdGvFYckH9URWghdJ/VSzZBwwBmizmaE949JntUM6qTfFIrip 3zzyVfVtH7B2Lzj4WQ8kAWj65+Txwm/2hs5XFlhCKdRU1uedTRsD04P49ZgSRY5QBLTc CQBCbVHZuVCB29pP2Co0mZAOf0TgkJUljtb0VB8CHI8VhuigYp30PE+r/D7MHanlVYxK BKS8ooZdHaU0PWi8nTHb08bOMRG7dMr/qLVaTlH87DKKqIpufZxi7ZRUHWNmW4PpK4km 2vlA== 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=TblIMkzhKEVNZyPa1dQf8kFQ+MgYlpgsesY6pOK1xME=; b=QaXbSW2q1+Aca8F9YA4viisGHj8GFELOUyREQ40nlQ3IU77fDl1xO1LgxILDN712x/ GfQJrzT2wCnYMmGebY0C4W3B+/DXWPFc8jzwRucqEj7y+ZbH+6jpSBvHV7T8/4DFCFBW a9A1dV6JT0atIm+Ws/kg1I4XUQBxgB9b8yUH2MdApdAfw7agGbawJNtxMFIq2b2nAUjC oTexOTuS7ESwII35OxDanQRfUCskE6RgI8F+DNasLfCW0z0BnC4VYzU64H5n2Nsv9low KVkIADVRqSJ2rNAX9yMjImkkWjj1TrbAlD7tT8XL2O4jNB4c2VyKe+B8QrVwtPJdnofu kzGw== X-Gm-Message-State: AOAM531KO994KUzaNwhJtXSp1KDN5TFY/3LHwnk+P+X72xByoOqOPxmH tQC7wAJ7+lLB7tIq5UGGdBvYt76W9C5/KH2ClFfcqw== X-Google-Smtp-Source: ABdhPJzjhN/4pCp12TIV+9JXZmAnmqzfEHd9/r8jgURCikDTNzP/FuiRKg13zAi0ZiROLKM3I1SNYAlTdBzPgSsKmW0= X-Received: by 2002:a17:902:341:: with SMTP id 59mr6129425pld.119.1591302328252; Thu, 04 Jun 2020 13:25:28 -0700 (PDT) MIME-Version: 1.0 References: <20200603233203.1695403-1-keescook@chromium.org> <20200603233203.1695403-4-keescook@chromium.org> <202006041316.A15D952@keescook> In-Reply-To: <202006041316.A15D952@keescook> From: Nick Desaulniers Date: Thu, 4 Jun 2020 13:25:16 -0700 Message-ID: Subject: Re: [PATCH 03/10] b43: Remove uninitialized_var() usage To: Kees Cook Cc: LKML , Linus Torvalds , Miguel Ojeda , Alexander Potapenko , Joe Perches , Andy Whitcroft , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , drbd-dev@lists.linbit.com, linux-block@vger.kernel.org, b43-dev@lists.infradead.org, Network Development , linux-wireless , linux-ide@vger.kernel.org, linux-clk@vger.kernel.org, linux-spi@vger.kernel.org, Linux Memory Management List , clang-built-linux Content-Type: text/plain; charset="UTF-8" Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, Jun 4, 2020 at 1:18 PM Kees Cook wrote: > > On Thu, Jun 04, 2020 at 01:08:44PM -0700, Nick Desaulniers wrote: > > On Wed, Jun 3, 2020 at 4:32 PM Kees Cook wrote: > > > > > > Using uninitialized_var() is dangerous as it papers over real bugs[1] > > > (or can in the future), and suppresses unrelated compiler warnings (e.g. > > > "unused variable"). If the compiler thinks it is uninitialized, either > > > simply initialize the variable or make compiler changes. As a precursor > > > to removing[2] this[3] macro[4], just initialize this variable to NULL, > > > and make the (unreachable!) code do a conditional test. > > > > > > [1] https://lore.kernel.org/lkml/20200603174714.192027-1-glider@google.com/ > > > [2] https://lore.kernel.org/lkml/CA+55aFw+Vbj0i=1TGqCR5vQkCzWJ0QxK6CernOU6eedsudAixw@mail.gmail.com/ > > > [3] https://lore.kernel.org/lkml/CA+55aFwgbgqhbp1fkxvRKEpzyR5J8n1vKT1VZdz9knmPuXhOeg@mail.gmail.com/ > > > [4] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/ > > > > > > Signed-off-by: Kees Cook > > > --- > > > drivers/net/wireless/broadcom/b43/phy_n.c | 10 +++++++--- > > > 1 file changed, 7 insertions(+), 3 deletions(-) > > > > > > diff --git a/drivers/net/wireless/broadcom/b43/phy_n.c b/drivers/net/wireless/broadcom/b43/phy_n.c > > > index d3c001fa8eb4..88cdcea10d61 100644 > > > --- a/drivers/net/wireless/broadcom/b43/phy_n.c > > > +++ b/drivers/net/wireless/broadcom/b43/phy_n.c > > > @@ -4222,7 +4222,7 @@ static void b43_nphy_tx_gain_table_upload(struct b43_wldev *dev) > > > > The TODOs and `#if 0` in this function are concerning. It looks like > > `rf_pwr_offset_table` is only used when `phy->rev` is >=7 && < 19. > > > > Further, the loop has a case for `phy->rev >= 19` but we would have > > returned earlier if that was the case. oh, and there's an early return for `phy->rev < 3` I just noticed. > > Yeah, that's why I put the "(unreachable!)" note in the commit log. ;) I don't think that note is correct. > > > > > > u32 rfpwr_offset; > > > u8 pga_gain, pad_gain; > > > int i; > > > - const s16 *uninitialized_var(rf_pwr_offset_table); > > > + const s16 *rf_pwr_offset_table = NULL; > > > > > > table = b43_nphy_get_tx_gain_table(dev); > > > if (!table) > > > @@ -4256,9 +4256,13 @@ static void b43_nphy_tx_gain_table_upload(struct b43_wldev *dev) > > > pga_gain = (table[i] >> 24) & 0xf; > > > pad_gain = (table[i] >> 19) & 0x1f; > > > if (b43_current_band(dev->wl) == NL80211_BAND_2GHZ) > > > - rfpwr_offset = rf_pwr_offset_table[pad_gain]; > > > + rfpwr_offset = rf_pwr_offset_table > > > + ? rf_pwr_offset_table[pad_gain] > > > + : 0; > > > else > > > - rfpwr_offset = rf_pwr_offset_table[pga_gain]; > > > + rfpwr_offset = rf_pwr_offset_table > > > + ? rf_pwr_offset_table[pga_gain] > > > + : 0; > > > > > > The code is trying to check `phy->rev >= 7 && phy->rev < 19` once > > before the loop, then set `rf_pwr_offset_table`, so having another > > conditional on `rf_pwr_offset_table` in the loop is unnecessary. I'm > > ok with initializing it to `NULL`, but I'm not sure the conditional > > check is necessary. Do you get a compiler warning otherwise? > > I mean, sort of the best thing to do is just remove nearly everything > here since it's actually unreachable. But it is commented as "when This code is reachable. Consider `phy->rev >= 7 && phy->rev < 19`. If `rf_pwr_offset_table` was NULL, it would have returned early on L4246, so the checks added in this patch are unnecessary. Forgive me if there's some other control flow I'm not considering. > supported ..." etc, so I figured I'd leave it. As part of that I didn't > want to leave any chance of a NULL deref, so I added the explicit tests > just for robustness. > > *shrug* -- Thanks, ~Nick Desaulniers