From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 141E4EE49AE for ; Tue, 22 Aug 2023 16:50:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237918AbjHVQuQ (ORCPT ); Tue, 22 Aug 2023 12:50:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57570 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234321AbjHVQuQ (ORCPT ); Tue, 22 Aug 2023 12:50:16 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B8C2E1BE; Tue, 22 Aug 2023 09:50:10 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 4C48E65B3C; Tue, 22 Aug 2023 16:50:10 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 21995C433C8; Tue, 22 Aug 2023 16:49:55 +0000 (UTC) Date: Tue, 22 Aug 2023 17:49:51 +0100 From: Catalin Marinas To: Mark Brown 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 , Szabolcs Nagy , "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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Fri, Aug 18, 2023 at 08:38:02PM +0100, Mark Brown wrote: > On Fri, Aug 18, 2023 at 06:29:54PM +0100, Catalin Marinas wrote: > > A related question - it may have been discussed intensively on the x86 > > thread (I may read it sometime) - why not have the libc map the shadow > > Your assumption that this is a single thread feels optimistic there. Yeah and I unfortunately ignored all of them. > > stack and pass the pointer/size to clone3()? It saves us from having to > > guess what the right size we'd need. struct clone_args is extensible. > > I can't recall or locate the specific reasoning there right now, perhaps > Rick or someone else can? I'd guess there would be compat concerns for > things that don't go via libc which would complicate the story with > identifying and marking things as GCS/SS safe, it's going to be more > robust to just supply a GCS if the process is using it. That said > having a default doesn't preclude us using the extensibility to allow > userspace directly to control the GCS size, I would certainly be in > favour of adding support for that. It would be good if someone provided a summary of the x86 decision (I'll get to those thread but most likely in September). I think we concluded that we can't deploy GCS entirely transparently, so we need a libc change (apart from the ELF annotations). Since libc is opting in to GCS, we could also update the pthread_create() etc. to allocate the shadow together with the standard stack. Anyway, that's my preference but maybe there were good reasons not to do this. -- Catalin