Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <47981665-0a97-7919-8eb0-e772e4035f39@intel.com>
Date:   Wed, 11 Jan 2023 16:13:17 -0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101
 Firefox/102.0 Thunderbird/102.6.1
Subject: Re: [PATCH 2/7] x86: Add CONFIG option X86_LASS
Content-Language: en-US
To:     Sohil Mehta <sohil.mehta@intel.com>,
        <linux-kernel@vger.kernel.org>, <x86@kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Ravi Shankar <ravi.v.shankar@intel.com>,
        "Tony Luck" <tony.luck@intel.com>, Paul Lai <paul.c.lai@intel.com>
References: <20230110055204.3227669-1-yian.chen@intel.com>
 <20230110055204.3227669-3-yian.chen@intel.com>
 <130a0ad6-31fd-dfe4-7b9a-cabb2e726349@intel.com>
From:   "Chen, Yian" <yian.chen@intel.com>
In-Reply-To: <130a0ad6-31fd-dfe4-7b9a-cabb2e726349@intel.com>
Content-Type: text/plain; charset="UTF-8"; format=flowed
Content-Transfer-Encoding: 8bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?QjJ1Wnh6eURYSjNqV1BucmlNekhVdkZyWDZ5RjdGQzFHWktIeGd3dlhzcEtq?=
 =?utf-8?B?bFRJMGNSdWRBL3hyL1Q5ZWxSeDZKUGwxK09qSUpLT0xzM1Jvc25kOFJ6bXow?=
 =?utf-8?B?NmhHbkZYc0JUWUpUK05oWSt5TndxekV1Z1dOQWhocmpQd1M1K3laS2ZuZUtO?=
 =?utf-8?B?Tmhka3RRMitCaFp1Nm5nV1IydGlqVThGMGRaZzNMQ1BIUmdyTnVZUUxiRGFQ?=
 =?utf-8?B?ZGdhc3V6NXAyQktSNkx6NS9xSkp2VGZoaGNGM21HMjhJNGg5MmE2OUl6eHAr?=
 =?utf-8?B?ak5uZUlzcC96dmVNT3N4NW1tOTRvTS9xbFdmNytHMTdrakpNNFY3ejhCbGlt?=
 =?utf-8?B?OVhCeHpFaEhqWEQ1L0hSaHVEUmZDQmZNZ1FwYzB3elIzMzMyWUx6ZHMveVJp?=
 =?utf-8?B?cUs3RkNYS0h6RDErRDFiS1VEWlBXR0taV1NleDZBMEExWlk2dFF6czhiWklO?=
 =?utf-8?B?Y2RGNzV6M2RkZ1kvQTZURDFWSVNMLzBUdzFuS2FGQ2JXL3lldndpcldBRTh3?=
 =?utf-8?B?Z3Y1VVpnN3Z3OW5LeVptTmdTUW1JNnM0eGtLRmRyMXFRbzluVFFFbEJQV09P?=
 =?utf-8?B?cUxXT1JZTkpWMER0aEdwZFhqckFlS3FCRmdnM2t1aFV3QTdSQkV5RGIvWXcw?=
 =?utf-8?B?NGxtSTF0NVluRHRTRTBaSlpEb2dQcHZ3ZzY1b1JrTElHMEV4MEx4UEtZVG1k?=
 =?utf-8?B?MUdpcDhwVXh1NXRxcTAvbzNJZk13akFkbURCcGMyVjR2VFIxeDFQQWYyODYy?=
 =?utf-8?B?REU5RnowdDVsT25qaGNzSWpZN1ZGTUQ0MytzUmVwR1BBTUtrL2V1UDh6dFVQ?=
 =?utf-8?B?UjZETklmV0JoUHZtdnZCd1hhSFpIZU5nNitPNjNYUTZJRUIzWnkyQVFDMitH?=
 =?utf-8?B?eDFUTTk5b1VUektidy83Vjh5OE93cG1Sd3JqUkR6V0E0NVNrd3E1eCtPcC9m?=
 =?utf-8?B?NWxxQkc0QW1mdzNWU1pMNkhYbmVGQ2VFdnhMeTRTeW1LYlBma2dwVTFjcmRR?=
 =?utf-8?B?L3NGemt5QnVVV0RJSXY1dVZwR3lSSS9BL0tmZHcxcGpiYkpWenZsWGI2MjRm?=
 =?utf-8?B?Y1I5Ynd1YVVyMXFwdkZyb3V1bkhTS1V3Yjhpa1B5Sk1nRzUyRVJJVWpkMlpr?=
 =?utf-8?B?TFNtaUhNM0RVVGNBbUlhdHJMQ2NqWmlFblVoM2l4aUp5ZkluUXBWYldwSHBj?=
 =?utf-8?B?YXBJa20wUUd6SXhHcXRWTTVOWkdlVkF5TzcwNTNqMnRpcG82c2FPRXVJdTBq?=
 =?utf-8?B?LzZ2dkVPUUthenJnVUszd05ZemloV0tsQ1d6ampjQjhGRE56NVIwcFh5ZS9W?=
 =?utf-8?B?TnVqcGxVWFh6NWxRTnBzTXZZNWgzWkFsVHJ0c0hOS2JYTThlYWRhMlhpYkZ2?=
 =?utf-8?B?bW0wSXAyb1l3TWxlUXBmN0xuc0dwV3JzYk83NDJwMWtYNFFJY3BYTTVDbU5D?=
 =?utf-8?B?U0dJU0ZrYW81ZWdnN0x2MGNZdWVvY3MwKytaS3NDd1FTM2JuTGpGeG01QVpD?=
 =?utf-8?B?eGN2QXpmbzNLYTByakVUYVdYM0xheUNIMzJGY1JNOWNlVTQ2RGRhVlNzMG9a?=
 =?utf-8?B?dVFTZGF5T0ZhZjlMUkRJWjA4cU1ob2lLRU9iOXlsb3FvQVcrWTV2b2VET21F?=
 =?utf-8?B?czJ5MGY1NklSMnpOZUUwaGw0S205UEJBOCt3TkhvTGYzN1FnVmZWZDlLc2FC?=
 =?utf-8?B?WXhoS2k5cFpxeU9BQnZqRWZtUE1Mb2E3ekFuazBYN1dHdWRLSUFwMDlRdHR5?=
 =?utf-8?B?aUZGRFdZWHAyS0hMakV3cU1KREtwY0hjVFppUWpZSHJWL3FGeS9XQi9Dd016?=
 =?utf-8?B?cGIzbFdjRS9JdnlCaG1qUm50cW01Y1pKVXhsNFhrZ1lmMHI0NWpDVGZZWU1G?=
 =?utf-8?B?UExabll0WE9NVXNQSFpCY3VaSTdCeWpJYUNYMnJ4VlBtOVRMbTZOQzI3b29s?=
 =?utf-8?B?NW9vS3l0dUZoMis1TXBYVElNMEFlK2ZwOVBOdDcwL0dtYXh2UmpaRVFmc3Er?=
 =?utf-8?B?ZTMvVUN4eFZoS0lPN0Nwc3VtOGM5cVl6K2hLbFNxMUFMVkI4ZS9DTXVhcCsy?=
 =?utf-8?B?cm92akdTWW91M2VlYWJvb1ZNeDAyMEsxMElJa3VISklGclZDbThac1N5U3h0?=
 =?utf-8?Q?GtQTteEgB6XDpHrFOcNbz1ZE7?=
X-MS-Exchange-CrossTenant-Network-Message-Id: f3142d18-8e23-47b7-b4a9-08daf431cffc
X-MS-Exchange-CrossTenant-AuthSource: DM4PR11MB5262.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 12 Jan 2023 00:13:20.7785
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: ZhTZsDZJ323WintZotyC3l6fUaP5oJvOyfkaqqa1THWLjjjKpmsIsoowuWOdp+fJIVNts5xjlpZ8VfI87pQ/1g==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR11MB5944
X-OriginatorOrg: intel.com
X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NICE_REPLY_A,
        RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,
        SPF_NONE autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


On 1/10/2023 1:05 PM, Sohil Mehta wrote:
> The subject can be better stated as:
> 
> x86/Kconfig: Add config option for LASS
> 
> On 1/9/2023 9:51 PM, Yian Chen wrote:
>> LASS is an Intel x86-64 only feature. 
> 
>> Add CONFIG
>> option X86_LASS and flag DISABLE_LASS to choose
>> opt-in/out the feature from kernel binary.
>> The second sentence is unnecessary.
> 
Sure, It makes sense to remove unnecessary sentence here.
>> CONFIG_X86_LASS is enabled by default because it
>> is a security feature which should have little
>> to no overhead or side effects. 
> 
> Doesn't it have a side effect that it modifies default vsyscall behavior?
> 
> I am guessing the impact of the vsyscall change would be minimal. 
> However, should LASS be disabled by default at least initially to 
> minimize the impact on userspace?
> 
> A follow-up patch can then enable this by default once the overall 
> impact is clearly known.
> 
>> If any issues are
>> found with specific use cases, the CONFIG option
>> makes it easy to disable.
>> This sentence is unnecessary.
> 
sure, I will remove this state too.

>> +config X86_LASS
>> +    def_bool y
>> +    prompt "Linear Address Space Separation"
>> +    depends on X86_64 && CPU_SUP_INTEL
>> +    help
>> +      Linear Address Space Separation (LASS) is a processor
>> +      feature that mitigates address space layout probes.
>> +
> 
> Let's try to be consistent about what LASS is expected to do. This 
> definition is very different from the one in patch 1/7.
> 
> Also, we should include some information here on how enabling the LASS 
> config option can impact vsyscall behavior.
> 
Sure, I will rewrite this help message and explain the impact to legacy 
vsyscall as well.

>> +      if unsure, say Y.
>> +
> 

thanks,
Yian