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 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id CFCDED3B7E2 for ; Mon, 8 Dec 2025 17:15:48 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 62C7010E035; Mon, 8 Dec 2025 17:15:48 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.b="Wr2nE4Yy"; dkim-atps=neutral Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.17]) by gabe.freedesktop.org (Postfix) with ESMTPS id B9DC810E035 for ; Mon, 8 Dec 2025 17:15:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1765214147; x=1796750147; h=date:from:to:cc:subject:message-id:references: mime-version:content-transfer-encoding:in-reply-to; bh=aqIhK+zLxmo0N7y7SE2iPZauIr5OwaWFbSt5XC+E7Hg=; b=Wr2nE4Yy3AAxEE3G7myXj9Kf6l2iMihAFepgEU6GCcDBis6IQIz+lI45 lTJ1Dt6aOHcbAgEJl1gGcCYPFLAv+8fjT8JGcchxt82PzXdRBEwqR17lm +dcE5nkD1YYQFoe9TTDYVQmXuR4NYJkkopmg7zXmhjotfYHn+46+fL5D2 IEBtUPqx8PiCc7GDsIkh3Ss0Ay8hTsB+yqBjr3QVILmxukXo/En7je6zm zCMuxwahEqDB0kMJrYg9hbRpAtAM8a7xnp0u/xT/WpO/k/F4X5y8O1Wm7 xWfRngs/8yaJn+O20Ub1RTZkVsBMh+j0l1kKYKUcaoprWvwB7EAbKdG8i w==; X-CSE-ConnectionGUID: 1Y9UCrAVTGeQsji7/ppFGQ== X-CSE-MsgGUID: Xkk0EMKFSaWvlCebkSS+vw== X-IronPort-AV: E=McAfee;i="6800,10657,11636"; a="67054713" X-IronPort-AV: E=Sophos;i="6.20,259,1758610800"; d="scan'208";a="67054713" Received: from fmviesa002.fm.intel.com ([10.60.135.142]) by fmvoesa111.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Dec 2025 09:15:46 -0800 X-CSE-ConnectionGUID: 6Z0C/4asSfK6fGz1HadzEw== X-CSE-MsgGUID: IJydUdr/QXamnkzkSKbwXw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.20,259,1758610800"; d="scan'208";a="219334896" Received: from rvuia-mobl.ger.corp.intel.com (HELO localhost) ([10.245.245.89]) by fmviesa002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Dec 2025 09:15:44 -0800 Date: Mon, 8 Dec 2025 19:15:42 +0200 From: Ville =?iso-8859-1?Q?Syrj=E4l=E4?= To: Krzysztof Karas Cc: intel-gfx@lists.freedesktop.org, Andi Shyti , Sebastian Brzezinka , Krzysztof Niemiec , Jani Nikula Subject: Re: [PATCH v5 3/3] drm: Avoid undefined behavior on u16 multiplication in drm_crtc_vblank_helper_get_vblank_timestamp_internal() Message-ID: References: <20251204143827.111428-1-krzysztof.karas@intel.com> <20251204143827.111428-4-krzysztof.karas@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20251204143827.111428-4-krzysztof.karas@intel.com> X-Patchwork-Hint: comment Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On Thu, Dec 04, 2025 at 02:38:27PM +0000, Krzysztof Karas wrote: > vpos (int) field multiplied by crtc_htotal (u16) may cause > implicit promotion of the latter and overflow the result causing > undefined behavior. How is that undefined? > > Cast the u16 operand to (s32) type to avoid that. > > Signed-off-by: Krzysztof Karas > --- > > v4: > * use s32 cast instead of int; > > drivers/gpu/drm/drm_vblank.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c > index 32d013c5c8fc..e25dcaa6cad4 100644 > --- a/drivers/gpu/drm/drm_vblank.c > +++ b/drivers/gpu/drm/drm_vblank.c > @@ -791,7 +791,7 @@ drm_crtc_vblank_helper_get_vblank_timestamp_internal( > * since start of scanout at first display scanline. delta_ns > * can be negative if start of scanout hasn't happened yet. > */ > - delta_ns = div_s64(1000000LL * (vpos * mode->crtc_htotal + hpos), > + delta_ns = div_s64(1000000LL * (vpos * (s32)mode->crtc_htotal + hpos), > mode->crtc_clock); > > /* Subtract time delta from raw timestamp to get final > -- > 2.34.1 -- Ville Syrjälä Intel