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Tue, 29 Oct 2024 23:41:53 +0000 Message-ID: <576e3c53-6417-4027-8d4c-b9f5703b634f@intel.com> Date: Tue, 29 Oct 2024 16:41:51 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 11/16] x86/vsyscall: Document the fact that vsyscall=emulate disables LASS To: Alexander Shishkin , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , , "H. Peter Anvin" , Peter Zijlstra , Ard Biesheuvel , "Paul E. McKenney" , Josh Poimboeuf , Xiongwei Song , Xin Li , "Mike Rapoport (IBM)" , Brijesh Singh , Michael Roth , Tony Luck , "Kirill A. Shutemov" , Alexey Kardashevskiy CC: Jonathan Corbet , Ingo Molnar , "Pawan Gupta" , Daniel Sneddon , Kai Huang , "Sandipan Das" , Breno Leitao , Rick Edgecombe , Alexei Starovoitov , Hou Tao , Juergen Gross , Vegard Nossum , Kees Cook , Eric Biggers , Jason Gunthorpe , "Masami Hiramatsu (Google)" , Andrew Morton , Luis Chamberlain , Yuntao Wang , "Rasmus Villemoes" , Christophe Leroy , Tejun Heo , Changbin Du , Huang Shijie , "Geert Uytterhoeven" , Namhyung Kim , Arnaldo Carvalho de Melo , , , , Dave Hansen References: <20241028160917.1380714-1-alexander.shishkin@linux.intel.com> <20241028160917.1380714-12-alexander.shishkin@linux.intel.com> Content-Language: en-US From: Sohil Mehta In-Reply-To: <20241028160917.1380714-12-alexander.shishkin@linux.intel.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BY1P220CA0004.NAMP220.PROD.OUTLOOK.COM (2603:10b6:a03:59d::15) To BYAPR11MB3320.namprd11.prod.outlook.com (2603:10b6:a03:18::25) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BYAPR11MB3320:EE_|MW4PR11MB7101:EE_ X-MS-Office365-Filtering-Correlation-Id: 45e28d0b-5f76-44dc-c461-08dcf8734433 X-LD-Processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|7416014|376014|921020; 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Both the patches are small enough and related to the same thing. > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index 1518343bbe22..4091dc48670a 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -7391,7 +7391,9 @@ > > emulate Vsyscalls turn into traps and are emulated > reasonably safely. The vsyscall page is > - readable. > + readable. This also disables the LASS > + feature to allow userspace to poke around > + the vsyscall page. > I am not sure if the person reading this guide would be aware of LASS. Also the way the sentence is structured it might be easy to misinterpret its meaning. How about something like: emulate Vsyscalls turn into traps and are emulated reasonably safely. The vsyscall page is readable. This disables the linear address space separation (LASS) security feature and makes the system less secure. > xonly [default] Vsyscalls turn into traps and are > emulated reasonably safely. The vsyscall