Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161464AbbKSUhM (ORCPT ); Thu, 19 Nov 2015 15:37:12 -0500 Received: from galahad.ideasonboard.com ([185.26.127.97]:33054 "EHLO galahad.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161170AbbKSUhK (ORCPT ); Thu, 19 Nov 2015 15:37:10 -0500 From: Laurent Pinchart To: Geert Uytterhoeven Cc: Greg Kroah-Hartman , Simon Horman , Magnus Damm , Yoshinori Sato , linux-serial@vger.kernel.org, linux-sh@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 09/25] serial: sh-sci: Avoid overflow in sci_baud_calc_hscif() Date: Thu, 19 Nov 2015 22:37:19 +0200 Message-ID: <4295635.bqyeD1RN5z@avalon> User-Agent: KMail/4.14.8 (Linux/4.0.9-gentoo; KDE/4.14.8; x86_64; ; ) In-Reply-To: <1447958344-836-10-git-send-email-geert+renesas@glider.be> References: <1447958344-836-1-git-send-email-geert+renesas@glider.be> <1447958344-836-10-git-send-email-geert+renesas@glider.be> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2346 Lines: 64 Hi Geert, Thank you for the patch. On Thursday 19 November 2015 19:38:48 Geert Uytterhoeven wrote: > If bps >= 1048576, the multiplication of "(sr * (1 << (2 * c + 1))" and > "bps" will overflow, and both br and err will contain bogus values. > Skip the current and all higher clock select predividers when overflow > is detected. Simplify the calculations using intermediates while we're > at it. > > Signed-off-by: Geert Uytterhoeven > --- > drivers/tty/serial/sh-sci.c | 14 ++++++++------ > 1 file changed, 8 insertions(+), 6 deletions(-) > > diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c > index fba1e1eea15dc3a1..97a0f8ef5adc55a2 100644 > --- a/drivers/tty/serial/sh-sci.c > +++ b/drivers/tty/serial/sh-sci.c > @@ -1870,7 +1870,7 @@ static unsigned int sci_scbrr_calc(struct sci_port *s, > unsigned int bps, static void sci_baud_calc_hscif(unsigned int bps, > unsigned long freq, int *brr, unsigned int *srr, unsigned int *cks) > { > - unsigned int sr, br, c; > + unsigned int sr, br, a, b, c; > int err, recv_margin; > int min_err = 1000; /* 100% */ > int recv_max_margin = 0; > @@ -1880,12 +1880,14 @@ static void sci_baud_calc_hscif(unsigned int bps, > unsigned long freq, int *brr, for (sr = 8; sr <= 32; sr++) { > for (c = 0; c <= 3; c++) { > /* integerized formulas from HSCIF documentation */ > - br = DIV_ROUND_CLOSEST(freq, (sr * > - (1 << (2 * c + 1)) * bps)); > + a = sr * (1 << (2 * c + 1)); > + if (bps > UINT_MAX / a) > + break; > + > + b = a * bps; This is becoming unreadable. Could you please use proper variable names ? A comment that explains the calculation would also be useful. > + br = DIV_ROUND_CLOSEST(freq, b); > br = clamp(br, 1U, 256U); > - err = DIV_ROUND_CLOSEST(freq, (br * bps * sr * > - (1 << (2 * c + 1)) / 1000)) - > - 1000; > + err = DIV_ROUND_CLOSEST(freq, (br * b) / 1000) - 1000; > /* Calc recv margin > * M: Receive margin (%) > * N: Ratio of bit rate to clock (N = sampling rate) -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/