From nobody Sat Jul 12 05:29:52 2025 Delivered-To: importer2@patchew.org Received-SPF: pass (zohomail.com: domain of vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; envelope-from=linux-kernel-owner@vger.kernel.org; helo=vger.kernel.org; Authentication-Results: mx.zohomail.com; spf=pass (zohomail.com: domain of vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail(p=none dis=none) header.from=arm.com Return-Path: Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mx.zohomail.com with SMTP id 1624274321283392.75602778156394; Mon, 21 Jun 2021 04:18:41 -0700 (PDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229789AbhFULUt (ORCPT ); Mon, 21 Jun 2021 07:20:49 -0400 Received: from foss.arm.com ([217.140.110.172]:32798 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229708AbhFULUo (ORCPT ); Mon, 21 Jun 2021 07:20:44 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6C687D6E; Mon, 21 Jun 2021 04:18:30 -0700 (PDT) Received: from e112269-lin.arm.com (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AE5C93F718; Mon, 21 Jun 2021 04:18:27 -0700 (PDT) From: Steven Price To: Catalin Marinas , Marc Zyngier , Will Deacon Cc: Steven Price , James Morse , Julien Thierry , Suzuki K Poulose , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Dave Martin , Mark Rutland , Thomas Gleixner , qemu-devel@nongnu.org, Juan Quintela , "Dr. David Alan Gilbert" , Richard Henderson , Peter Maydell , Andrew Jones Subject: [PATCH v17 1/6] arm64: mte: Sync tags for pages where PTE is untagged Date: Mon, 21 Jun 2021 12:17:11 +0100 Message-Id: <20210621111716.37157-2-steven.price@arm.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20210621111716.37157-1-steven.price@arm.com> References: <20210621111716.37157-1-steven.price@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" A KVM guest could store tags in a page even if the VMM hasn't mapped the page with PROT_MTE. So when restoring pages from swap we will need to check to see if there are any saved tags even if !pte_tagged(). However don't check pages for which pte_access_permitted() returns false as these will not have been swapped out. Reviewed-by: Catalin Marinas Signed-off-by: Steven Price --- arch/arm64/include/asm/mte.h | 4 ++-- arch/arm64/include/asm/pgtable.h | 22 +++++++++++++++++++--- arch/arm64/kernel/mte.c | 18 +++++++++++++----- 3 files changed, 34 insertions(+), 10 deletions(-) diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h index bc88a1ced0d7..347ef38a35f7 100644 --- a/arch/arm64/include/asm/mte.h +++ b/arch/arm64/include/asm/mte.h @@ -37,7 +37,7 @@ void mte_free_tag_storage(char *storage); /* track which pages have valid allocation tags */ #define PG_mte_tagged PG_arch_2 =20 -void mte_sync_tags(pte_t *ptep, pte_t pte); +void mte_sync_tags(pte_t old_pte, pte_t pte); void mte_copy_page_tags(void *kto, const void *kfrom); void mte_thread_init_user(void); void mte_thread_switch(struct task_struct *next); @@ -53,7 +53,7 @@ int mte_ptrace_copy_tags(struct task_struct *child, long = request, /* unused if !CONFIG_ARM64_MTE, silence the compiler */ #define PG_mte_tagged 0 =20 -static inline void mte_sync_tags(pte_t *ptep, pte_t pte) +static inline void mte_sync_tags(pte_t old_pte, pte_t pte) { } static inline void mte_copy_page_tags(void *kto, const void *kfrom) diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgta= ble.h index 0b10204e72fc..db5402168841 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -314,9 +314,25 @@ static inline void set_pte_at(struct mm_struct *mm, un= signed long addr, if (pte_present(pte) && pte_user_exec(pte) && !pte_special(pte)) __sync_icache_dcache(pte); =20 - if (system_supports_mte() && - pte_present(pte) && pte_tagged(pte) && !pte_special(pte)) - mte_sync_tags(ptep, pte); + /* + * If the PTE would provide user space access to the tags associated + * with it then ensure that the MTE tags are synchronised. Although + * pte_access_permitted() returns false for exec only mappings, they + * don't expose tags (instruction fetches don't check tags). + */ + if (system_supports_mte() && pte_access_permitted(pte, false) && + !pte_special(pte)) { + pte_t old_pte =3D READ_ONCE(*ptep); + /* + * We only need to synchronise if the new PTE has tags enabled + * or if swapping in (in which case another mapping may have + * set tags in the past even if this PTE isn't tagged). + * (!pte_none() && !pte_present()) is an open coded version of + * is_swap_pte() + */ + if (pte_tagged(pte) || (!pte_none(old_pte) && !pte_present(old_pte))) + mte_sync_tags(old_pte, pte); + } =20 __check_racy_pte_update(mm, ptep, pte); =20 diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c index 125a10e413e9..69b3fde8759e 100644 --- a/arch/arm64/kernel/mte.c +++ b/arch/arm64/kernel/mte.c @@ -32,10 +32,9 @@ DEFINE_STATIC_KEY_FALSE(mte_async_mode); EXPORT_SYMBOL_GPL(mte_async_mode); #endif =20 -static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_= swap) +static void mte_sync_page_tags(struct page *page, pte_t old_pte, + bool check_swap, bool pte_is_tagged) { - pte_t old_pte =3D READ_ONCE(*ptep); - if (check_swap && is_swap_pte(old_pte)) { swp_entry_t entry =3D pte_to_swp_entry(old_pte); =20 @@ -43,6 +42,9 @@ static void mte_sync_page_tags(struct page *page, pte_t *= ptep, bool check_swap) return; } =20 + if (!pte_is_tagged) + return; + page_kasan_tag_reset(page); /* * We need smp_wmb() in between setting the flags and clearing the @@ -55,16 +57,22 @@ static void mte_sync_page_tags(struct page *page, pte_t= *ptep, bool check_swap) mte_clear_page_tags(page_address(page)); } =20 -void mte_sync_tags(pte_t *ptep, pte_t pte) +void mte_sync_tags(pte_t old_pte, pte_t pte) { struct page *page =3D pte_page(pte); long i, nr_pages =3D compound_nr(page); bool check_swap =3D nr_pages =3D=3D 1; + bool pte_is_tagged =3D pte_tagged(pte); + + /* Early out if there's nothing to do */ + if (!check_swap && !pte_is_tagged) + return; =20 /* if PG_mte_tagged is set, tags have already been initialised */ for (i =3D 0; i < nr_pages; i++, page++) { if (!test_and_set_bit(PG_mte_tagged, &page->flags)) - mte_sync_page_tags(page, ptep, check_swap); + mte_sync_page_tags(page, old_pte, check_swap, + pte_is_tagged); } } =20 --=20 2.20.1