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Thu, 25 Mar 2021 03:23:09 -0700 (PDT) Sender: Guenter Roeck Date: Thu, 25 Mar 2021 03:23:07 -0700 From: Guenter Roeck To: Yangbo Lu Cc: netdev@vger.kernel.org, Richard Cochran Subject: Re: [PATCH] ptp_qoriq: fix overflow in ptp_qoriq_adjfine() u64 calcalation Message-ID: <20210325102307.GA163632@roeck-us.net> References: <20210323080229.28283-1-yangbo.lu@nxp.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210323080229.28283-1-yangbo.lu@nxp.com> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Mar 23, 2021 at 04:02:29PM +0800, Yangbo Lu wrote: > Current calculation for diff of TMR_ADD register value may have > 64-bit overflow in this code line, when long type scaled_ppm is > large. > > adj *= scaled_ppm; > > This patch is to resolve it by using mul_u64_u64_div_u64(). > > Signed-off-by: Yangbo Lu > Acked-by: Richard Cochran > --- > drivers/ptp/ptp_qoriq.c | 13 +++++++------ > 1 file changed, 7 insertions(+), 6 deletions(-) > > diff --git a/drivers/ptp/ptp_qoriq.c b/drivers/ptp/ptp_qoriq.c > index 68beb1bd07c0..f7f220700cb5 100644 > --- a/drivers/ptp/ptp_qoriq.c > +++ b/drivers/ptp/ptp_qoriq.c > @@ -189,15 +189,16 @@ int ptp_qoriq_adjfine(struct ptp_clock_info *ptp, long scaled_ppm) > tmr_add = ptp_qoriq->tmr_add; > adj = tmr_add; > > - /* calculate diff as adj*(scaled_ppm/65536)/1000000 > - * and round() to the nearest integer > + /* > + * Calculate diff and round() to the nearest integer > + * > + * diff = adj * (ppb / 1000000000) > + * = adj * scaled_ppm / 65536000000 > */ > - adj *= scaled_ppm; > - diff = div_u64(adj, 8000000); > - diff = (diff >> 13) + ((diff >> 12) & 1); > + diff = mul_u64_u64_div_u64(adj, scaled_ppm, 32768000000); mul_u64_u64_div_u64() is not exported. As result, every build with CONFIG_PTP_1588_CLOCK_QORIQ=m (ie every allmodconfig build) fails with: ERROR: modpost: "mul_u64_u64_div_u64" [drivers/ptp/ptp-qoriq.ko] undefined! or a similar error. Guenter