[PATCH net] enetc: Avoid implicit sign extension

Static analysis tool reports:
"Suspicious implicit sign extension - 'flags' with type u8 (8 bit,
unsigned) is promoted in 'flags' << 24 to type int (32 bits, signed),
then sign-extended to type unsigned long long (64 bits, unsigned).
If flags << 24 is greater than 0x7FFFFFFF, the upper bits of the result
will all be 1."

Use lower_32_bits() to avoid this scenario.

Signed-off-by: Claudiu Manoil <claudiu.manoil@nxp.com>
---
 drivers/net/ethernet/freescale/enetc/enetc_hw.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/freescale/enetc/enetc_hw.h b/drivers/net/ethernet/freescale/enetc/enetc_hw.h
index 00938f7960a4..07e03df8af94 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc_hw.h
+++ b/drivers/net/ethernet/freescale/enetc/enetc_hw.h

@@ -535,8 +535,8 @@ static inline __le32 enetc_txbd_set_tx_start(u64 tx_start, u8 flags)
 {
 	u32 temp;
 
-	temp = (tx_start >> 5 & ENETC_TXBD_TXSTART_MASK) |
-	       (flags << ENETC_TXBD_FLAGS_OFFSET);
+	temp = lower_32_bits(tx_start >> 5 & ENETC_TXBD_TXSTART_MASK) |
+	       (u32)(flags << ENETC_TXBD_FLAGS_OFFSET);
 
 	return cpu_to_le32(temp);
 }

-- 
2.25.1

-----Original Message-----
From: Claudiu Manoil <claudiu.manoil@nxp.com>
Sent: Monday, March 29, 2021 4:35 PM
To: netdev@vger.kernel.org
Cc: Jakub Kicinski <kuba@kernel.org>; David S . Miller
[off-list ref]; Vladimir Oltean [off-list ref]
Subject: [PATCH net] enetc: Avoid implicit sign extension

Static analysis tool reports:
"Suspicious implicit sign extension - 'flags' with type u8 (8 bit,
unsigned) is promoted in 'flags' << 24 to type int (32 bits, signed),
then sign-extended to type unsigned long long (64 bits, unsigned).
If flags << 24 is greater than 0x7FFFFFFF, the upper bits of the result
will all be 1."

Use lower_32_bits() to avoid this scenario.

Fixes: 82728b91f124 ("enetc: Remove Tx checksumming offload code")