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 X-Spam-Level: X-Spam-Status: No, score=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5F339C433E9 for ; Tue, 9 Feb 2021 11:44:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 24CB064E7C for ; Tue, 9 Feb 2021 11:44:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230334AbhBILm3 (ORCPT ); Tue, 9 Feb 2021 06:42:29 -0500 Received: from mail.kernel.org ([198.145.29.99]:48992 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230239AbhBILfx (ORCPT ); Tue, 9 Feb 2021 06:35:53 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id E2DBB64E6C; Tue, 9 Feb 2021 11:35:08 +0000 (UTC) Date: Tue, 9 Feb 2021 11:35:06 +0000 From: Catalin Marinas To: Vincenzo Frascino Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, Andrew Morton , Will Deacon , Dmitry Vyukov , Andrey Ryabinin , Alexander Potapenko , Marco Elver , Evgenii Stepanov , Branislav Rankov , Andrey Konovalov , Lorenzo Pieralisi Subject: Re: [PATCH v12 4/7] arm64: mte: Enable TCO in functions that can read beyond buffer limits Message-ID: <20210209113505.GD1435@arm.com> References: <20210208165617.9977-1-vincenzo.frascino@arm.com> <20210208165617.9977-5-vincenzo.frascino@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210208165617.9977-5-vincenzo.frascino@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 08, 2021 at 04:56:14PM +0000, Vincenzo Frascino wrote: > diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h > index 0deb88467111..f43d78aee593 100644 > --- a/arch/arm64/include/asm/uaccess.h > +++ b/arch/arm64/include/asm/uaccess.h > @@ -188,6 +188,21 @@ static inline void __uaccess_enable_tco(void) > ARM64_MTE, CONFIG_KASAN_HW_TAGS)); > } > > +/* Whether the MTE asynchronous mode is enabled. */ > +DECLARE_STATIC_KEY_FALSE(mte_async_mode); > + > +static inline void __uaccess_disable_tco_async(void) > +{ > + if (static_branch_unlikely(&mte_async_mode)) > + __uaccess_disable_tco(); > +} > + > +static inline void __uaccess_enable_tco_async(void) > +{ > + if (static_branch_unlikely(&mte_async_mode)) > + __uaccess_enable_tco(); > +} I would add a comment here along the lines of what's in the commit log: these functions disable tag checking only if in MTE async mode since the sync mode generates exceptions synchronously and the nofault or load_unaligned_zeropad can handle them. > + > static inline void uaccess_disable_privileged(void) > { > __uaccess_disable_tco(); > @@ -307,8 +322,10 @@ do { \ > do { \ > int __gkn_err = 0; \ > \ > + __uaccess_enable_tco_async(); \ > __raw_get_mem("ldr", *((type *)(dst)), \ > (__force type *)(src), __gkn_err); \ > + __uaccess_disable_tco_async(); \ > if (unlikely(__gkn_err)) \ > goto err_label; \ > } while (0) > @@ -379,9 +396,11 @@ do { \ > #define __put_kernel_nofault(dst, src, type, err_label) \ > do { \ > int __pkn_err = 0; \ > + __uaccess_enable_tco_async(); \ > \ Nitpick: for consistency with the __get_kernel_nofault() function, please move the empty line above __uaccess_enable_tco_async(). > __raw_put_mem("str", *((type *)(src)), \ > (__force type *)(dst), __pkn_err); \ > + __uaccess_disable_tco_async(); \ > if (unlikely(__pkn_err)) \ > goto err_label; \ > } while(0) [...] > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > index 92078e1eb627..60531afc706e 100644 > --- a/arch/arm64/kernel/mte.c > +++ b/arch/arm64/kernel/mte.c > @@ -27,6 +27,10 @@ u64 gcr_kernel_excl __ro_after_init; > > static bool report_fault_once = true; > > +/* Whether the MTE asynchronous mode is enabled. */ > +DEFINE_STATIC_KEY_FALSE(mte_async_mode); > +EXPORT_SYMBOL_GPL(mte_async_mode); > + > static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap) > { > pte_t old_pte = READ_ONCE(*ptep); > @@ -170,6 +174,12 @@ void mte_enable_kernel_sync(void) > void mte_enable_kernel_async(void) > { > __mte_enable_kernel("asynchronous", SCTLR_ELx_TCF_ASYNC); > + > + /* > + * This function is called on each active smp core, we do not > + * to take cpu_hotplug_lock again. > + */ > + static_branch_enable_cpuslocked(&mte_async_mode); > } Do we need to disable mte_async_mode in mte_enable_kernel_sync()? I think currently that's only done at boot time but kasan may gain some run-time features and change the mode dynamically. -- Catalin