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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id B7690C83F17 for ; Mon, 28 Jul 2025 12:47:28 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 27A746B0088; Mon, 28 Jul 2025 08:47:28 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 22B286B0089; Mon, 28 Jul 2025 08:47:28 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 11A456B008A; Mon, 28 Jul 2025 08:47:28 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 0122D6B0088 for ; Mon, 28 Jul 2025 08:47:27 -0400 (EDT) Received: from smtpin10.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 82066160254 for ; Mon, 28 Jul 2025 12:47:27 +0000 (UTC) X-FDA: 83713649334.10.78B30C9 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf27.hostedemail.com (Postfix) with ESMTP id DBA8F40008 for ; Mon, 28 Jul 2025 12:47:25 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=fVrLDUF6; spf=pass (imf27.hostedemail.com: domain of will@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=will@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1753706846; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=bzb8t/6nORtGXVRimdsT6Upco6zC0qWd4/4ieZdsy5o=; b=K1GNXFV0qbgUlTdSzHca1ibPM74M1LlbPyfkubtMN+bOzPfzl8wEM36p0rRHDNq65fu6zk SIegltjp96zCsd8MwpmAVdY4CEmSDvXZYMNH4obKnhbsxXhgaXJz9lGrK5LFSr6mNI1oog P/l0YbdengFqzMhS39RxMLYlgI1SNig= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1753706846; a=rsa-sha256; cv=none; b=xkDhRxdKAGyClr1C4S3rygkq7bRTv3LePkW7e9IDFm0m7FM3eaFcoTPDRoCKozMd/UxAId V33RmfCLvRjJJ3L1o4LujZyRyWnkbqGAc6WlwDtvYgHRBh3D+XLqtGPg0ZQK3J6isIiafC aulH18GaO0EyhdRN3JXMpSHo5ynjDHw= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=fVrLDUF6; spf=pass (imf27.hostedemail.com: domain of will@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=will@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id 8EFD75C414C; Mon, 28 Jul 2025 12:47:24 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D6A14C4CEE7; Mon, 28 Jul 2025 12:47:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1753706844; bh=8erufKMpAOmnBQJD5AQN3zyqiuSStzu2grxssP0lTyk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=fVrLDUF6ALvU1+rw08l0PQQfJJ7diMMEUvcuQzJIilzrRSpYwOlOYK2n15xwoyML4 D4v1V5ouoPMP5Uz79ByW5/BerCfgE3utI4NZmRpjthPrhH6zfjhuvxxdwBw/nduyx5 BrLlHsjfIfQLUwiEsrKJ7Z00EUM59kWy8WUBrjuxruXI8VGjRYFATJyEOBskkNPuBj cOwpUVMCLcgqoD5XxSL62JtvLUxMBr1zB0b3M8fPyxY2JnP4ebqJETtie1/WquwywI lFApDm1CkeeTMlruPIC1tMlq6jstGhB1R7LebnE8eV6IkSurORWhWXOaOc/cTwOFqR 53bl3DIV1aZJA== Date: Mon, 28 Jul 2025 13:47:14 +0100 From: Will Deacon To: Sami Tolvanen Cc: Deepak Gupta , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Masahiro Yamada , Nathan Chancellor , Nicolas Schier , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Nick Desaulniers , Bill Wendling , Monk Chiang , Kito Cheng , Justin Stitt , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-mm@kvack.org, llvm@lists.linux.dev, rick.p.edgecombe@intel.com, broonie@kernel.org, cleger@rivosinc.com, apatel@ventanamicro.com, ajones@ventanamicro.com, conor.dooley@microchip.com, charlie@rivosinc.com, samuel.holland@sifive.com, bjorn@rivosinc.com, fweimer@redhat.com, jeffreyalaw@gmail.com, heinrich.schuchardt@canonical.com, andrew@sifive.com, ved@rivosinc.com Subject: Re: [PATCH 10/11] scs: generic scs code updated to leverage hw assisted shadow stack Message-ID: References: <20250724-riscv_kcfi-v1-0-04b8fa44c98c@rivosinc.com> <20250724-riscv_kcfi-v1-10-04b8fa44c98c@rivosinc.com> <20250725161327.GC1724026@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250725161327.GC1724026@google.com> X-Rspamd-Queue-Id: DBA8F40008 X-Stat-Signature: 46waisn1wxsga91zuiteyxu6kchgpzo9 X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1753706845-611360 X-HE-Meta: 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 Q/LavTEQ wF94iis8chGrsvGfDpE+I1eJwSBxbKevzXtjy2ssEcWXo7PSnIXs19bx6fA1F1MmhMmPXgc9/GCLhlBflvJfYTV14a8+9hXV2tNGvPGi0yni+475tKYZ20pInecZw9eLjCWv8etx0I9NQdVpGGcikDbnPn9ReJhd6cz+TYynkJ/CYAfxe8zv/7bsDQ785R4Rc5UnpcLxttBGyk+Tta7heH9WHucjFqUMt2/5aAa8Rcp7wM5yXAg0ZRsg0L6R4P+0b5RNyqItxzx/Iv2jgqqQqmfHUEpPPWTk84WJ37AV4957EsMx7Hn1jhEHL/ISUNIO+IK6sBrJpCOHOFV85VrwHXekn5DOPNuEv1sVjh0jDFT7wxkc= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jul 25, 2025 at 04:13:27PM +0000, Sami Tolvanen wrote: > On Thu, Jul 24, 2025 at 04:37:03PM -0700, Deepak Gupta wrote: > > diff --git a/include/linux/scs.h b/include/linux/scs.h > > index 4ab5bdc898cf..6ceee07c2d1a 100644 > > --- a/include/linux/scs.h > > +++ b/include/linux/scs.h > > @@ -12,6 +12,7 @@ > > #include > > #include > > #include > > +#include > > > > #ifdef CONFIG_SHADOW_CALL_STACK > > > > @@ -37,22 +38,45 @@ static inline void scs_task_reset(struct task_struct *tsk) > > * Reset the shadow stack to the base address in case the task > > * is reused. > > */ > > +#ifdef CONFIG_ARCH_HAS_KERNEL_SHADOW_STACK > > + task_scs_sp(tsk) = task_scs(tsk) + SCS_SIZE; > > +#else > > task_scs_sp(tsk) = task_scs(tsk); > > +#endif > > } > > > > static inline unsigned long *__scs_magic(void *s) > > { > > +#ifdef CONFIG_ARCH_HAS_KERNEL_SHADOW_STACK > > + return (unsigned long *)(s); > > +#else > > return (unsigned long *)(s + SCS_SIZE) - 1; > > +#endif > > } > > > > static inline bool task_scs_end_corrupted(struct task_struct *tsk) > > { > > unsigned long *magic = __scs_magic(task_scs(tsk)); > > - unsigned long sz = task_scs_sp(tsk) - task_scs(tsk); > > + unsigned long sz; > > + > > +#ifdef CONFIG_ARCH_HAS_KERNEL_SHADOW_STACK > > + sz = (task_scs(tsk) + SCS_SIZE) - task_scs_sp(tsk); > > +#else > > + sz = task_scs_sp(tsk) - task_scs(tsk); > > +#endif > > > > return sz >= SCS_SIZE - 1 || READ_ONCE_NOCHECK(*magic) != SCS_END_MAGIC; > > } > > > > +static inline void __scs_store_magic(unsigned long *s, unsigned long magic_val) > > +{ > > +#ifdef CONFIG_ARCH_HAS_KERNEL_SHADOW_STACK > > + arch_scs_store(s, magic_val); > > +#else > > + *__scs_magic(s) = magic_val; > > +#endif > > +} > > + > > I'm not a huge fan of all the ifdefs. We could clean this up by > allowing architectures to simply override some these functions, or at > least use if (IS_ENABLED(CONFIG...)) instead. Will, any thoughts about > this? Yeah, I agree that allowing architectures to provide overrides makes sense, however I also suspect that some of this needs to be a runtime decision because not all CPUs will support the hardware-accelerated feature and will presumably want to fall back on the software implementation. Will