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Sat, 13 Dec 2025 00:17:10 +0000 Message-ID: Date: Fri, 12 Dec 2025 16:17:06 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/3] x86: Extend LASS support to EFI configurations To: Ard Biesheuvel CC: , Dave Hansen , "Thomas Gleixner" , Ingo Molnar , "Borislav Petkov" , "H . Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Kiryl Shutsemau , Rick Edgecombe , Andrew Cooper , Tony Luck , "Alexander Shishkin" , , References: <20251204072143.3636863-1-sohil.mehta@intel.com> <5fb937b4-5459-4894-a107-945bfb50a701@intel.com> Content-Language: en-US From: Sohil Mehta In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SJ0PR03CA0263.namprd03.prod.outlook.com (2603:10b6:a03:3a0::28) To DS0PR11MB7997.namprd11.prod.outlook.com (2603:10b6:8:125::14) Precedence: bulk X-Mailing-List: linux-efi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS0PR11MB7997:EE_|DS0PR11MB8133:EE_ X-MS-Office365-Filtering-Correlation-Id: 0eafac20-50de-47aa-8b8e-08de39dcf568 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|376014|7416014|1800799024|366016; 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Ah, I missed that efi_check_for_embedded_firmwares() remaps the regions. > >> LASS wouldn't care whether there is an actual mapping behind the >> address. It only relies on the MSB for enforcement. So, any code that >> relied on accessing boot services memory before efi_free_boot_services() >> could get affected by LASS. >> > > This only applies to code that accesses boot services memory via a > mapping in the lower range. > Yes, I was referring to usages which use the lower mapping. Though, efi_check_for_embedded_firmwares() doesn't do that, enabling LASS after freeing boot services memory is still the right thing to do. In theory, someone could use the 1:1 mapping.