From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F34D662B for ; Fri, 18 Aug 2023 17:30:01 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 61717C433C7; Fri, 18 Aug 2023 17:29:56 +0000 (UTC) Date: Fri, 18 Aug 2023 18:29:54 +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> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Aug 09, 2023 at 04:34:38PM +0100, Mark Brown wrote: > On Wed, Aug 09, 2023 at 03:24:14PM +0100, Catalin Marinas wrote: > > On Mon, Aug 07, 2023 at 11:00:08PM +0100, Mark Brown wrote: > > > +* When set PR_SHADOW_STACK_ENABLE flag allocates a Guarded Control Stack for > > > > The 'for' at the end of the line above is not needed. > > > > > + and enables GCS for the thread, enabling the functionality controlled by > > I find it a little clearer that it's a per thread stack here but sure. If it reads better for you, feel free to keep it as is. > > > +3. Allocation of Guarded Control Stacks > > > +---------------------------------------- > > > > +* When GCS is enabled for a thread a new Guarded Control Stack will be > > > + allocated for it of size RLIMIT_STACK / 2 or 2 gigabytes, whichever is > > > + smaller. > > > Is this number based on the fact that a function call would only push > > the LR to GCS while standard function prologue pushes at least two > > registers? > > It's actually based on bitrot that I'd initially chosen a smaller value > since it's likely that functions will push at least something as you > suggest, the patches now just use RLIMIT_STACK. I'll fix. 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 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 plan to get back next week to this series, I'll need to read a bit more on the spec) -- Catalin