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=-6.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=ham 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 7D85EC43603 for ; Mon, 9 Dec 2019 09:51:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4B75324684 for ; Mon, 9 Dec 2019 09:51:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=baylibre-com.20150623.gappssmtp.com header.i=@baylibre-com.20150623.gappssmtp.com header.b="1QP8E5rE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727260AbfLIJvR (ORCPT ); Mon, 9 Dec 2019 04:51:17 -0500 Received: from mail-wm1-f65.google.com ([209.85.128.65]:53697 "EHLO mail-wm1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727200AbfLIJvQ (ORCPT ); Mon, 9 Dec 2019 04:51:16 -0500 Received: by mail-wm1-f65.google.com with SMTP id n9so14200268wmd.3 for ; Mon, 09 Dec 2019 01:51:15 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=baylibre-com.20150623.gappssmtp.com; s=20150623; h=references:user-agent:from:to:cc:subject:in-reply-to:date :message-id:mime-version; bh=/lV4JOds+hQfSWH7coNmWVW3vJirPTXEaWuWEYduTYk=; b=1QP8E5rEnnpU1XZQRU97MeWENs2Clw1QWJ71vLW8hAfEkhPVRwKXiPNjy/x0GSLHYy iEBd0l9DIz9rS1Oyx0EPugmBekdTVFsgULtW+CLZXn6/HjLgmtUzplUdlOsDM5LAUDj0 ZcxA33nqqE0xugQ3p8BMXNCeyP1AYFooYXFa5XI0QPTEhBKECdxMuXuvxVKG7YuiLuvu HcyR3Y2Qfj6WJ/wDGu3KhySAy/so+P9mJ6kfLB8OW3wCl4ZRytOKZZXu2Ml1Q45RY5jB fTuVR/SzH8ZWZBk7CdkFP5J3sdSMCEMFKPUnlAg2AJyR7r3onPgGF9+GTHCkZZdD9moJ 1SZA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:references:user-agent:from:to:cc:subject :in-reply-to:date:message-id:mime-version; bh=/lV4JOds+hQfSWH7coNmWVW3vJirPTXEaWuWEYduTYk=; b=gOtNxGAlHPQBJdgIoEur1OFLHDlIpk4+AY9DOapLPoDJsNdOLoA7MMcktNVRuDuM6I vsfMbXNDg6BxEtrB1+B0spyreVxzc9AJi3lfGpojBLoaf7HwTKVYwryiSaXxw+lYK+hl hRcz9n5my6wG1iOVpqButwLlspAtp2uCKubFczUxXTUdBSuKLVe4mQ63u06YDdP3Rh43 tZ1ms5CrZJ/o1uFJjOdyCN1z5xxG3LneAKt3l2iXH0PTkg6ZNikDwX2fXg5U44ukawET jv4ebK/eLRf9IHXB3huF+m6y0VnheXzkoL0O4IpTDuyM/KHS9unz6fEcQhHV97AIr4UN JDWQ== X-Gm-Message-State: APjAAAV1fUfV20eAnbVcXVDJfdGJNKEyBhaU6gbEb39tbiUH1B9BarhJ H68KDzRCu9pkj/fPcGo3TRaVSw== X-Google-Smtp-Source: APXvYqyJrZdhijAo9WBhDx6CQX/GMWF1YJMIkaeUQIf7KJnAzbt8wQFio/hP1vuXx3Nyfi9YFWG7zg== X-Received: by 2002:a1c:238c:: with SMTP id j134mr24393284wmj.151.1575885074948; Mon, 09 Dec 2019 01:51:14 -0800 (PST) Received: from localhost (laubervilliers-658-1-213-31.w90-63.abo.wanadoo.fr. [90.63.244.31]) by smtp.gmail.com with ESMTPSA id y6sm25826838wrl.17.2019.12.09.01.51.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Dec 2019 01:51:14 -0800 (PST) References: <20191208212206.16808-1-repk@triplefau.lt> User-agent: mu4e 1.3.3; emacs 26.2 From: Jerome Brunet To: Remi Pommarel , Neil Armstrong Cc: Michael Turquette , Stephen Boyd , Kevin Hilman , linux-amlogic@lists.infradead.org, linux-clk@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] clk: meson: pll: Fix by 0 division in __pll_params_to_rate() In-reply-to: <20191208212206.16808-1-repk@triplefau.lt> Date: Mon, 09 Dec 2019 10:51:13 +0100 Message-ID: <1jo8whesj2.fsf@starbuckisacylon.baylibre.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-clk-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-clk@vger.kernel.org On Sun 08 Dec 2019 at 22:22, Remi Pommarel wrote: > Some meson pll registers can be initialized with 0 as N value, introducing > the following division by 0 when computing rate : > > UBSAN: Undefined behaviour in drivers/clk/meson/clk-pll.c:75:9 > division by zero > CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.4.0-rc3-608075-g86c9af8630e1-dirty #400 > Call trace: > dump_backtrace+0x0/0x1c0 > show_stack+0x14/0x20 > dump_stack+0xc4/0x100 > ubsan_epilogue+0x14/0x68 > __ubsan_handle_divrem_overflow+0x98/0xb8 > __pll_params_to_rate+0xdc/0x140 > meson_clk_pll_recalc_rate+0x278/0x3a0 > __clk_register+0x7c8/0xbb0 > devm_clk_hw_register+0x54/0xc0 > meson_eeclkc_probe+0xf4/0x1a0 > platform_drv_probe+0x54/0xd8 > really_probe+0x16c/0x438 > driver_probe_device+0xb0/0xf0 > device_driver_attach+0x94/0xa0 > __driver_attach+0x70/0x108 > bus_for_each_dev+0xd8/0x128 > driver_attach+0x30/0x40 > bus_add_driver+0x1b0/0x2d8 > driver_register+0xbc/0x1d0 > __platform_driver_register+0x78/0x88 > axg_driver_init+0x18/0x20 > do_one_initcall+0xc8/0x24c > kernel_init_freeable+0x2b0/0x344 > kernel_init+0x10/0x128 > ret_from_fork+0x10/0x18 > > This checks if N is null before doing the division. Thanks for reporting this > > Fixes: 8289aafa4f36 ("clk: meson: improve pll driver results with > frac") In mainline, the commit above went in with sha1 3c4fe763d64d. Also, this commit is not really responsible for the problem. Having HW initialized with N = 0 would have failed since the beginning, I believe. In this case the correct fixes would be: Fixes: 7a29a869434e ("clk: meson: Add support for Meson clock controller") > Signed-off-by: Remi Pommarel > --- > drivers/clk/meson/clk-pll.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/clk/meson/clk-pll.c b/drivers/clk/meson/clk-pll.c > index ddb1e5634739..6649659f216a 100644 > --- a/drivers/clk/meson/clk-pll.c > +++ b/drivers/clk/meson/clk-pll.c > @@ -66,6 +66,10 @@ static unsigned long __pll_params_to_rate(unsigned long parent_rate, > (1 << pll->frac.width)); > } > > + /* Avoid by zero division */ > + if (n == 0) > + return 0; This can only really happen after init, in recalc() rate. I would much prefer if you could check the n value right after it is read (meson_parm_read()) in .recalc_rate() and add a comment explaining that some HW may have this parameter set 0 on init. > + > return DIV_ROUND_UP_ULL(rate, n); > }