linux-kernel - [PATCH AUTOSEL 5.11 29/38] ptp_qoriq: fix overflow in ptp_qoriq

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Date:   Mon, 29 Mar 2021 18:21:24 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Yangbo Lu <yangbo.lu@....com>,
        "David S . Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>, netdev@...r.kernel.org
Subject: [PATCH AUTOSEL 5.11 29/38] ptp_qoriq: fix overflow in ptp_qoriq_adjfine() u64 calcalation

From: Yangbo Lu <yangbo.lu@....com>

[ Upstream commit f51d7bf1dbe5522c51c93fe8faa5f4abbdf339cd ]

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 <yangbo.lu@....com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 beb5f74944cd..08f4cf0ad9e3 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);
+	diff = DIV64_U64_ROUND_UP(diff, 2);
 
 	tmr_add = neg_adj ? tmr_add - diff : tmr_add + diff;
-
 	ptp_qoriq->write(&regs->ctrl_regs->tmr_add, tmr_add);
 
 	return 0;
-- 
2.30.1