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Sun, 22 Nov 2020 16:42:47 +0000 From: "Chatradhi, Naveen Krishna" To: Guenter Roeck CC: Salvatore Bonaccorso , "linux-hwmon@vger.kernel.org" , "naveenkrishna.ch@gmail.com" , "stable@vger.kernel.org" Subject: RE: [PATCH] hwmon: amd_energy: modify the visibility of the counters Thread-Topic: [PATCH] hwmon: amd_energy: modify the visibility of the counters Thread-Index: AQHWuRhfPkP7JZ+0TkWLTfmjzaPqdanEvyEAgAFY1QCADa3pgIAAbySAgAAyaVA= Date: Sun, 22 Nov 2020 16:42:47 +0000 Message-ID: References: <20201112172159.8781-1-nchatrad@amd.com> <238e3cf7-582f-a265-5300-9b44948107b0@roeck-us.net> <20201113135834.GA354992@eldamar.lan> <20201122133011.GA48943@roeck-us.net> In-Reply-To: <20201122133011.GA48943@roeck-us.net> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: msip_labels: MSIP_Label_c3918902-4ff3-42f6-8eb5-e5d9c71daf16_Enabled=true; MSIP_Label_c3918902-4ff3-42f6-8eb5-e5d9c71daf16_SetDate=2020-11-22T16:41:35Z; MSIP_Label_c3918902-4ff3-42f6-8eb5-e5d9c71daf16_Method=Privileged; 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x-ms-exchange-antispam-messagedata: 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 x-ms-exchange-transport-forked: True Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: DM6PR12MB4388.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: bc6b75ed-8c93-496a-9584-08d88f05a48d X-MS-Exchange-CrossTenant-originalarrivaltime: 22 Nov 2020 16:42:47.0260 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: HNowbI9IW992OOXbr+VY5TUEmX2dm25RnBOzM7Ale/WrWCqoqQ3skoca85Qqv3dgOD7tMmMFRf8oTikRM7cHYg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR12MB3116 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org [AMD Official Use Only - Approved for External Use] Hi Guenter, > A much better fix would have been to cache RAPL data for a short period o= f time. To avoid any possibility of attacks, maybe add some random interval= . Something like this: Thanks for the tip, I will check this out. > In accumulate_delta(): > accums->next_update =3D jiffies + HZ / 2 + get_random_int % HZ; > In amd_energy_read(): > accum =3D &data->accums[channel]; > if (time_after(accum->next_update)) Do you mean if (time_after(jiffies, accum->next_update)) > accumulate_delta(data, channel, cpu, reg); > *val =3D div64_ul(accum->energy_ctr * 1000000UL, BIT(data->energy_= units)); > and drop amd_add_delta(). Regards, Naveenk -----Original Message----- From: Guenter Roeck =20 Sent: Sunday, November 22, 2020 7:00 PM To: Chatradhi, Naveen Krishna Cc: Salvatore Bonaccorso ; linux-hwmon@vger.kernel.org; = naveenkrishna.ch@gmail.com; stable@vger.kernel.org Subject: Re: [PATCH] hwmon: amd_energy: modify the visibility of the counte= rs [CAUTION: External Email] On Sun, Nov 22, 2020 at 06:56:24AM +0000, Chatradhi, Naveen Krishna wrote: > [AMD Official Use Only - Approved for External Use] > > Hi Guenter, Salvatore > > > This is very unusual, and may mess up the "sensors" command. > > What problem is this trying to solve ? > Guenter, sorry for the delayed response. > This fix is required to address the possible side channel attack reported= in CVE-2020-12912. > [ ... ] > > >> ? > Yes, Salvatore, thanks for bringing the links. > A much better fix would have been to cache RAPL data for a short period of = time. To avoid any possibility of attacks, maybe add some random interval. = Something like this: In accumulate_delta(): accums->next_update =3D jiffies + HZ / 2 + get_random_int % HZ; In amd_energy_read(): accum =3D &data->accums[channel]; if (time_after(accum->next_update)) accumulate_delta(data, channel, cpu, reg); *val =3D div64_ul(accum->energy_ctr * 1000000UL, BIT(data->energy_u= nits)); and drop amd_add_delta(). Guenter