From nobody Mon Apr 6 12:53:28 2026 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6704DC54EE9 for ; Wed, 7 Sep 2022 11:00:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229908AbiIGLAh (ORCPT ); Wed, 7 Sep 2022 07:00:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59200 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229915AbiIGLA2 (ORCPT ); Wed, 7 Sep 2022 07:00:28 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id D385286FF4 for ; Wed, 7 Sep 2022 04:00:26 -0700 (PDT) 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 B4DAE106F; Wed, 7 Sep 2022 04:00:32 -0700 (PDT) Received: from e119884-lin.cambridge.arm.com (e119884-lin.cambridge.arm.com [10.1.196.72]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8A3B43F7B4; Wed, 7 Sep 2022 04:00:25 -0700 (PDT) From: Vincenzo Frascino To: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com Cc: Vincenzo Frascino , Catalin Marinas , Will Deacon Subject: [PATCH v2] mte: Initialize tag storage to KASAN_TAG_INVALID Date: Wed, 7 Sep 2022 12:00:15 +0100 Message-Id: <20220907110015.11489-1-vincenzo.frascino@arm.com> X-Mailer: git-send-email 2.37.3 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" When the kernel is entered on aarch64, the MTE allocation tags are in an UNKNOWN state. With MTE enabled, the tags are initialized: - When a page is allocated and the user maps it with PROT_MTE. - On allocation, with in-kernel MTE enabled (HW_TAGS KASAN). If the tag pool is zeroed by the hardware at reset, it makes it difficult to track potential places where the initialization of the tags was missed. This can be observed under QEMU for aarch64, which initializes the MTE allocation tags to zero. Initialize to tag storage to KASAN_TAG_INVALID to catch potential places where the initialization of the tags was missed. This is done introducing a new kernel command line parameter "mte.tags_init" that enables the debug option. Note: The proposed solution should be considered a debug option because it might have performance impact on large machines at boot. Cc: Catalin Marinas Cc: Will Deacon Signed-off-by: Vincenzo Frascino --- arch/arm64/kernel/mte.c | 47 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 47 insertions(+) diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c index b2b730233274..af9a8eba9be4 100644 --- a/arch/arm64/kernel/mte.c +++ b/arch/arm64/kernel/mte.c @@ -6,6 +6,7 @@ #include #include #include +#include #include #include #include @@ -35,6 +36,8 @@ DEFINE_STATIC_KEY_FALSE(mte_async_or_asymm_mode); EXPORT_SYMBOL_GPL(mte_async_or_asymm_mode); #endif =20 +static bool mte_tags_init __ro_after_init; + static void mte_sync_page_tags(struct page *page, pte_t old_pte, bool check_swap, bool pte_is_tagged) { @@ -98,6 +101,48 @@ int memcmp_pages(struct page *page1, struct page *page2) return ret; } =20 +/* mte.tags_init=3Doff/on */ +static int __init early_mte_tags_init(char *arg) +{ + if (!arg) + return -EINVAL; + + if (!strcmp(arg, "off")) + mte_tags_init =3D false; + else if (!strcmp(arg, "on")) + mte_tags_init =3D true; + else + return -EINVAL; + + return 0; +} +early_param("mte.tags_init", early_mte_tags_init); + +static inline void __mte_tag_storage_init(void) +{ + static bool mte_tags_uninitialized =3D true; + phys_addr_t pa_start, pa_end; + u64 index; + + if (mte_tags_init && !mte_tags_uninitialized) + return; + + for_each_mem_range(index, &pa_start, &pa_end) { + void *va_start =3D (void *)__phys_to_virt(pa_start); + void *va_end =3D (void *)__phys_to_virt(pa_end); + size_t va_size =3D (u64)va_end - (u64)va_start; + + if (va_start >=3D va_end) + break; + + mte_set_mem_tag_range(va_start, va_size, KASAN_TAG_INVALID, false); + } + + /* Tags are now initialized to KASAN_TAG_INVALID */ + mte_tags_uninitialized =3D false; + pr_info("MTE: Tag Storage Initialized\n"); +} + static inline void __mte_enable_kernel(const char *mode, unsigned long tcf) { /* Enable MTE Sync Mode for EL1. */ @@ -105,6 +150,8 @@ static inline void __mte_enable_kernel(const char *mode= , unsigned long tcf) SYS_FIELD_PREP(SCTLR_EL1, TCF, tcf)); isb(); =20 + __mte_tag_storage_init(); + pr_info_once("MTE: enabled in %s mode at EL1\n", mode); } =20 --=20 2.37.3