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=-11.4 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 6852CC388F2 for ; Thu, 22 Oct 2020 07:34:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 23C75223C7 for ; Thu, 22 Oct 2020 07:34:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2508588AbgJVHeP (ORCPT ); Thu, 22 Oct 2020 03:34:15 -0400 Received: from mx2.suse.de ([195.135.220.15]:59490 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2506555AbgJVHeO (ORCPT ); Thu, 22 Oct 2020 03:34:14 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id B6DC5B195; Thu, 22 Oct 2020 07:34:12 +0000 (UTC) Subject: Re: [PATCH 1/1] video: fbdev: fix divide error in fbcon_switch To: saeed.mirzamohammadi@oracle.com, linux-kernel@vger.kernel.org Cc: linux-fbdev@vger.kernel.org, b.zolnierkie@samsung.com, jani.nikula@intel.com, daniel.vetter@ffwll.ch, gustavoars@kernel.org, dri-devel@lists.freedesktop.org, akpm@linux-foundation.org, rppt@kernel.org References: <20201021235758.59993-1-saeed.mirzamohammadi@oracle.com> From: Thomas Zimmermann Message-ID: Date: Thu, 22 Oct 2020 09:34:11 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.2 MIME-Version: 1.0 In-Reply-To: <20201021235758.59993-1-saeed.mirzamohammadi@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi On 22.10.20 01:57, saeed.mirzamohammadi@oracle.com wrote: > From: Saeed Mirzamohammadi > > This patch fixes the issue due to: > > [ 89.572883] divide_error: 0000 [#1] SMP KASAN PTI > [ 89.572897] CPU: 3 PID: 16083 Comm: repro Not tainted 5.9.0-rc7.20200930.rc1.allarch-19-g3e32d0d.syzk #5 > [ 89.572902] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.5.1 01/01/2011 > [ 89.572934] RIP: 0010:cirrusfb_check_var+0x84/0x1260 BTW, if you run qemu with cirrus, there's also a DRM driver named cirrus.ko. Might be a better choice than the old fbdev driver. If you just care about qemu, but not the actual graphics device, take a look at https://www.kraxel.org/blog/2014/10/qemu-using-cirrus-considered-harmful/ Anyway, thanks for your patch. Best regards Thomas > > The error happens when the pixels value is calculated before performing the sanity checks on bits_per_pixel. > A bits_per_pixel set to zero causes divide by zero error. > > This patch moves the calculation after the sanity check. > > Signed-off-by: Saeed Mirzamohammadi > Tested-by: Saeed Mirzamohammadi > --- > drivers/video/fbdev/cirrusfb.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/video/fbdev/cirrusfb.c b/drivers/video/fbdev/cirrusfb.c > index 15a9ee7cd734..a7749101b094 100644 > --- a/drivers/video/fbdev/cirrusfb.c > +++ b/drivers/video/fbdev/cirrusfb.c > @@ -531,7 +531,7 @@ static int cirrusfb_check_var(struct fb_var_screeninfo *var, > { > int yres; > /* memory size in pixels */ > - unsigned pixels = info->screen_size * 8 / var->bits_per_pixel; > + unsigned int pixels; > struct cirrusfb_info *cinfo = info->par; > > switch (var->bits_per_pixel) { > @@ -573,6 +573,7 @@ static int cirrusfb_check_var(struct fb_var_screeninfo *var, > return -EINVAL; > } > > + pixels = info->screen_size * 8 / var->bits_per_pixel; > if (var->xres_virtual < var->xres) > var->xres_virtual = var->xres; > /* use highest possible virtual resolution */ > -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Felix Imendörffer