From patchwork Wed Apr 6 18:09:20 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Catalin Marinas X-Patchwork-Id: 12803966 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D509AC433EF for ; Wed, 6 Apr 2022 18:10:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=IyY6yIGi9+wJvVyJgl7TQ45xMcYxFgAtehtNULca+qY=; b=0VM7HGqXBnH15w yOJr86A47DnwcQc03SBfW9pZ4TnIemuyZvAytSyORv4l2mT6LLkVjuOxcuuO0VZjFpvkOYVCiLVUn 3TZYWXf6m5QNWBv9LShiAooFBHcDKCSy/cbX1PJm4ayxFdOxF9kDZJKJNHQ6jnvjmX60DKY3Chfla /1Vh7qNwuOlvKIIFPiXUFBxi9fahhARornX++vItfdfy5uj9oeFSeZf2xK1J/vX7ZKfw3jIvkNMdH x/XoYJQ5EqjEl+uEAe7GLUKMfCV9zZZYOmKC7s8IztyQ7bwfP4WflICgZqlhyrAvEzNFsxKQmqjpj 7LEzOu1/nE4tJx86QieQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1ncA68-007SvU-Lh; Wed, 06 Apr 2022 18:09:40 +0000 Received: from dfw.source.kernel.org ([139.178.84.217]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1ncA5z-007SsV-3M for linux-arm-kernel@lists.infradead.org; Wed, 06 Apr 2022 18:09:32 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 9E6FA61B89; Wed, 6 Apr 2022 18:09:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8B6F7C385A9; Wed, 6 Apr 2022 18:09:27 +0000 (UTC) From: Catalin Marinas To: Linus Torvalds , Andreas Gruenbacher , Josef Bacik Cc: Al Viro , Andrew Morton , Chris Mason , David Sterba , Will Deacon , linux-fsdevel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v3 1/3] mm: Add fault_in_subpage_writeable() to probe at sub-page granularity Date: Wed, 6 Apr 2022 19:09:20 +0100 Message-Id: <20220406180922.1522433-2-catalin.marinas@arm.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20220406180922.1522433-1-catalin.marinas@arm.com> References: <20220406180922.1522433-1-catalin.marinas@arm.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220406_110931_256121_4D9CE795 X-CRM114-Status: GOOD ( 23.50 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On hardware with features like arm64 MTE or SPARC ADI, an access fault can be triggered at sub-page granularity. Depending on how the fault_in_writeable() function is used, the caller can get into a live-lock by continuously retrying the fault-in on an address different from the one where the uaccess failed. In the majority of cases progress is ensured by the following conditions: 1. copy_to_user_nofault() guarantees at least one byte access if the user address is not faulting. 2. The fault_in_writeable() loop is resumed from the first address that could not be accessed by copy_to_user_nofault(). If the loop iteration is restarted from an earlier (initial) point, the loop is repeated with the same conditions and it would live-lock. Introduce an arch-specific probe_subpage_writeable() and call it from the newly added fault_in_subpage_writeable() function. The arch code with sub-page faults will have to implement the specific probing functionality. Note that no other fault_in_subpage_*() functions are added since they have no callers currently susceptible to a live-lock. Signed-off-by: Catalin Marinas Cc: Andrew Morton --- arch/Kconfig | 7 +++++++ include/linux/pagemap.h | 1 + include/linux/uaccess.h | 22 ++++++++++++++++++++++ mm/gup.c | 29 +++++++++++++++++++++++++++++ 4 files changed, 59 insertions(+) diff --git a/arch/Kconfig b/arch/Kconfig index 29b0167c088b..b34032279926 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -24,6 +24,13 @@ config KEXEC_ELF config HAVE_IMA_KEXEC bool +config ARCH_HAS_SUBPAGE_FAULTS + bool + help + Select if the architecture can check permissions at sub-page + granularity (e.g. arm64 MTE). The probe_user_*() functions + must be implemented. + config HOTPLUG_SMT bool diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 993994cd943a..6165283bdb6f 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -1046,6 +1046,7 @@ void folio_add_wait_queue(struct folio *folio, wait_queue_entry_t *waiter); * Fault in userspace address range. */ size_t fault_in_writeable(char __user *uaddr, size_t size); +size_t fault_in_subpage_writeable(char __user *uaddr, size_t size); size_t fault_in_safe_writeable(const char __user *uaddr, size_t size); size_t fault_in_readable(const char __user *uaddr, size_t size); diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index 546179418ffa..8bbb2dabac19 100644 --- a/include/linux/uaccess.h +++ b/include/linux/uaccess.h @@ -231,6 +231,28 @@ static inline bool pagefault_disabled(void) */ #define faulthandler_disabled() (pagefault_disabled() || in_atomic()) +#ifndef CONFIG_ARCH_HAS_SUBPAGE_FAULTS + +/** + * probe_subpage_writeable: probe the user range for write faults at sub-page + * granularity (e.g. arm64 MTE) + * @uaddr: start of address range + * @size: size of address range + * + * Returns 0 on success, the number of bytes not probed on fault. + * + * It is expected that the caller checked for the write permission of each + * page in the range either by put_user() or GUP. The architecture port can + * implement a more efficient get_user() probing if the same sub-page faults + * are triggered by either a read or a write. + */ +static inline size_t probe_subpage_writeable(void __user *uaddr, size_t size) +{ + return 0; +} + +#endif /* CONFIG_ARCH_HAS_SUBPAGE_FAULTS */ + #ifndef ARCH_HAS_NOCACHE_UACCESS static inline __must_check unsigned long diff --git a/mm/gup.c b/mm/gup.c index f598a037eb04..501bc150792c 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1648,6 +1648,35 @@ size_t fault_in_writeable(char __user *uaddr, size_t size) } EXPORT_SYMBOL(fault_in_writeable); +/** + * fault_in_subpage_writeable - fault in an address range for writing + * @uaddr: start of address range + * @size: size of address range + * + * Fault in a user address range for writing while checking for permissions at + * sub-page granularity (e.g. arm64 MTE). This function should be used when + * the caller cannot guarantee forward progress of a copy_to_user() loop. + * + * Returns the number of bytes not faulted in (like copy_to_user() and + * copy_from_user()). + */ +size_t fault_in_subpage_writeable(char __user *uaddr, size_t size) +{ + size_t faulted_in; + + /* + * Attempt faulting in at page granularity first for page table + * permission checking. The arch-specific probe_subpage_writeable() + * functions may not check for this. + */ + faulted_in = size - fault_in_writeable(uaddr, size); + if (faulted_in) + faulted_in -= probe_subpage_writeable(uaddr, faulted_in); + + return size - faulted_in; +} +EXPORT_SYMBOL(fault_in_subpage_writeable); + /* * fault_in_safe_writeable - fault in an address range for writing * @uaddr: start of address range