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Thu, 10 Aug 2023 08:56:14 +0000 Date: Thu, 10 Aug 2023 09:55:50 +0100 From: Szabolcs Nagy To: Mark Brown , Catalin Marinas Cc: Will Deacon , Jonathan Corbet , Andrew Morton , Marc Zyngier , Oliver Upton , James Morse , Suzuki K Poulose , Arnd Bergmann , Oleg Nesterov , Eric Biederman , Kees Cook , Shuah Khan , "Rick P. Edgecombe" , Deepak Gupta , Ard Biesheuvel , "H.J. Lu" , Paul Walmsley , Palmer Dabbelt , Albert Ou , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org Subject: Re: [PATCH v4 03/36] arm64/gcs: Document the ABI for Guarded Control Stacks Message-ID: References: <20230807-arm64-gcs-v4-0-68cfa37f9069@kernel.org> <20230807-arm64-gcs-v4-3-68cfa37f9069@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: SA1P222CA0098.NAMP222.PROD.OUTLOOK.COM (2603:10b6:806:35e::8) To DB9PR08MB7179.eurprd08.prod.outlook.com (2603:10a6:10:2cc::19) MIME-Version: 1.0 X-MS-TrafficTypeDiagnostic: DB9PR08MB7179:EE_|AS2PR08MB9618:EE_|DBAEUR03FT050:EE_|AS2PR08MB9523:EE_ X-MS-Office365-Filtering-Correlation-Id: 00be4314-86e6-435a-b5d0-08db997faf64 x-checkrecipientrouted: true NoDisclaimer: true X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam-Untrusted: BCL:0; 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I'll fix. the pcs requires 16byte aligned stack frames, with 8byte per gcs entry there is no need for same gcs size as stack size in userspace. you can argue about a fixed size small increment (stacksize/2 + inc) for signal handling on alt stack and special tokens, but stack size is overkill i think. fwiw my current makecontext patch uses roundup(stacksize/2+160). (threads guaranteed to have about 300bytes of data on the stack in glibc so if gcs is stacksize/2, that accounts for the increment. this is for the theoretical case when an empty thread just tries to overflow the stack and then handle the fault on sigaltstack.)