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Miller" Subject: Re: [PATCH net v2] enetc: Avoid implicit sign extension Thread-Topic: [PATCH net v2] enetc: Avoid implicit sign extension Thread-Index: AQHXJKXlZqB1plpeA0OcVM38+bWT0qqbJqaA Date: Mon, 29 Mar 2021 16:24:22 +0000 Message-ID: <20210329162421.k5ltz2tkufsueyds@skbuf> References: <20210329141443.23245-1-claudiu.manoil@nxp.com> In-Reply-To: <20210329141443.23245-1-claudiu.manoil@nxp.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: nxp.com; dkim=none (message not signed) header.d=none;nxp.com; dmarc=none action=none header.from=nxp.com; x-originating-ip: [5.12.16.165] x-ms-publictraffictype: Email x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: 8c2e520f-f3d9-4524-194f-08d8f2cf1ca9 x-ms-traffictypediagnostic: VI1PR04MB6942: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:8882; x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; 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charset="us-ascii" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: nxp.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: VI1PR04MB5136.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 8c2e520f-f3d9-4524-194f-08d8f2cf1ca9 X-MS-Exchange-CrossTenant-originalarrivaltime: 29 Mar 2021 16:24:22.4941 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 686ea1d3-bc2b-4c6f-a92c-d99c5c301635 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: sbbQ0HPIOySOJ4nKuhM+rEgJ6H1/15BsJar6bfPLKm9nWuPTQjwLbKBBfVyv7DiOCVE/XOnD5ea6RjEOHZXfGQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI1PR04MB6942 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Mon, Mar 29, 2021 at 05:14:43PM +0300, Claudiu Manoil wrote: > 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 This is a backwards way of saying 'if flags & BIT(7) is set', no? But BIT(7) is ENETC_TXBD_FLAGS_F (the 'final BD' bit), and I've been testing SO_TXTIME with single BD frames, and haven't seen this problem. > will all be 1." >=20 > Use lower_32_bits() to avoid this scenario. >=20 > Fixes: 82728b91f124 ("enetc: Remove Tx checksumming offload code") >=20 > Signed-off-by: Claudiu Manoil > --- > v2 - added 'fixes' tag >=20 > drivers/net/ethernet/freescale/enetc/enetc_hw.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) >=20 > diff --git a/drivers/net/ethernet/freescale/enetc/enetc_hw.h b/drivers/ne= t/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_s= tart, u8 flags) > { > u32 temp; > =20 > - temp =3D (tx_start >> 5 & ENETC_TXBD_TXSTART_MASK) | > - (flags << ENETC_TXBD_FLAGS_OFFSET); > + temp =3D lower_32_bits(tx_start >> 5 & ENETC_TXBD_TXSTART_MASK) | > + (u32)(flags << ENETC_TXBD_FLAGS_OFFSET); I don't actually understand why lower_32_bits called on the TX time helps, considering that the value is masked already. The static analysis tool says that the right hand side of the "|" operator is what is sign-extended: (flags << ENETC_TXBD_FLAGS_OFFSET); Isn't it sufficient that you replace "u8 flags" in the function prototype with "u32 flags"? > =20 > return cpu_to_le32(temp); > } > --=20 > 2.25.1 > =