From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 382E63DFC65 for ; Tue, 26 May 2026 11:17:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779794276; cv=none; b=Uw8I63k+m/mvWSL1bECdJ8R1fy+7x1cuid8BQ7SgYUXnsBy3Moxvb9Z1H1PMInLG3T2Gv//tIgcgRD4An5t/gyYoXfGaN9UCnzVm/nAIvr/JrH0SQZL295vi7N4blwTcNy83E7BqZ3sLmbL/Nmex6Uo70knhpf4EhRHGSTxEBYw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779794276; c=relaxed/simple; bh=FwJkibkCBOdtFacZl+Z5KjOcoULy9AB4XvS2nXgTrfE=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=D3+O24HwKOfQ3Q4fZn9f39YbzEKaCfd7EZQlgSb8KnjVKhb9282IeYQHXlCuOYCWwxhyCNxkYQOl+SJUwWYbBresEG2n4nAgSlo6GQG5RCBZuThmd0xI0krAJSOun6fIUro6EzvAC1IEXk1Va4H4ZX/gYwcEVdINh/eouEOcLZU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=Nn4RkJoL; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="Nn4RkJoL" 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 B5A35169C; Tue, 26 May 2026 04:17:49 -0700 (PDT) Received: from localhost.localdomain (e123572-lin.cambridge.arm.com [10.1.194.54]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E95EE3F7D8; Tue, 26 May 2026 04:17:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1779794274; bh=FwJkibkCBOdtFacZl+Z5KjOcoULy9AB4XvS2nXgTrfE=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=Nn4RkJoLmryKMcVWDZAo2G9SJrXDVC2e2IVuX/B4SuByLHEZPp3EyUsOPRPwgnKi6 u2JIa00peJahtdJ4OiA0FfTH8N4jRfG9r7HvRDrqlEhilfbnhdNzlAkCn7kk69m/5g wdoPZfIR93zdMSoyz0ZavQj7CwZPq+wYJJ0iqOnI= From: Kevin Brodsky Date: Tue, 26 May 2026 12:16:00 +0100 Subject: [PATCH RFC v8 11/24] mm: kpkeys: Introduce kpkeys_hardened_pgtables feature Precedence: bulk X-Mailing-List: linux-hardening@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260526-kpkeys-v8-11-eaaacdacc67c@arm.com> References: <20260526-kpkeys-v8-0-eaaacdacc67c@arm.com> In-Reply-To: <20260526-kpkeys-v8-0-eaaacdacc67c@arm.com> To: linux-hardening@vger.kernel.org Cc: Kevin Brodsky , Andrew Morton , Andy Lutomirski , Catalin Marinas , Dave Hansen , "David Hildenbrand (Arm)" , Ira Weiny , Jann Horn , Jeff Xu , Joey Gouly , Kees Cook , Linus Walleij , Marc Zyngier , Mark Brown , Matthew Wilcox , Maxwell Bland , "Mike Rapoport (IBM)" , Peter Zijlstra , Pierre Langlois , Quentin Perret , Rick Edgecombe , Ryan Roberts , Vlastimil Babka , Will Deacon , Yang Shi , Yeoreum Yun , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, x86@kernel.org, Lorenzo Stoakes , Thomas Gleixner X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=ed25519-sha256; t=1779794212; l=5797; i=kevin.brodsky@arm.com; s=20260427; h=from:subject:message-id; bh=FwJkibkCBOdtFacZl+Z5KjOcoULy9AB4XvS2nXgTrfE=; b=2cUTS8rHt18AsAstVm0NGzVThMD7m5Y67bLhIkADws+GYq1Gk7VC/5rzaVdp7P+4+Kt/pmT4Z oudsu0Y2wlWDejRI1Ya9DPrboy1WjZKr1FzWCgjzCZ4t/G+vItNf9AV X-Developer-Key: i=kevin.brodsky@arm.com; a=ed25519; pk=N2QG+eJKrvkNovwhhwJhnJ4+ScVfsGCHldmqLfcMTFs= kpkeys_hardened_pgtables is a hardening feature based on kpkeys. It aims to prevent the corruption of page tables by: 1. mapping all page table pages, both kernel and user, with a privileged pkey (KPKEYS_PKEY_PGTABLES), and 2. granting write access to that pkey only when running at in a privileged kpkeys context (KPKEYS_CTX_PGTABLES). This patch introduces basic infrastructure; the implementation of both aspects will follow. The feature is exposed as CONFIG_KPKEYS_HARDENED_PGTABLES; it requires explicit architecture opt-in by selecting ARCH_HAS_KPKEYS_HARDENED_PGTABLES, since much of the page table handling is arch-specific. Because this feature relies on kpkeys being available and enabled, and modifies attributes of the linear map, it must be inactive on boot. kpkeys_hardened_pgtables_init() enables it by toggling a static key; this function must be called by supported architectures in mem_init(), before any call to pagetable_alloc() is made. Supported architectures must also provide arch_supports_kpkeys_early() in . This will be used during early boot to detect whether kpkeys_hardened_pgtables is going to be enabled (e.g. to decide how to allocate early page tables). Signed-off-by: Kevin Brodsky --- include/asm-generic/kpkeys.h | 4 ++++ include/linux/kpkeys.h | 40 +++++++++++++++++++++++++++++++++++++++- mm/Kconfig | 3 +++ mm/Makefile | 1 + mm/kpkeys_hardened_pgtables.c | 16 ++++++++++++++++ security/Kconfig.hardening | 12 ++++++++++++ 6 files changed, 75 insertions(+), 1 deletion(-) diff --git a/include/asm-generic/kpkeys.h b/include/asm-generic/kpkeys.h index ab819f157d6a..cec92334a9f3 100644 --- a/include/asm-generic/kpkeys.h +++ b/include/asm-generic/kpkeys.h @@ -2,6 +2,10 @@ #ifndef __ASM_GENERIC_KPKEYS_H #define __ASM_GENERIC_KPKEYS_H +#ifndef KPKEYS_PKEY_PGTABLES +#define KPKEYS_PKEY_PGTABLES 1 +#endif + #ifndef KPKEYS_PKEY_DEFAULT #define KPKEYS_PKEY_DEFAULT 0 #endif diff --git a/include/linux/kpkeys.h b/include/linux/kpkeys.h index 0ce0db80b4ee..d413a17f8882 100644 --- a/include/linux/kpkeys.h +++ b/include/linux/kpkeys.h @@ -4,11 +4,13 @@ #include #include +#include #define KPKEYS_CTX_DEFAULT 0 +#define KPKEYS_CTX_PGTABLES 1 #define KPKEYS_CTX_MIN KPKEYS_CTX_DEFAULT -#define KPKEYS_CTX_MAX KPKEYS_CTX_DEFAULT +#define KPKEYS_CTX_MAX KPKEYS_CTX_PGTABLES /* * ... is used to discard extra arguments - this allows users of this macro @@ -119,4 +121,40 @@ static inline bool kpkeys_enabled(void) #endif /* CONFIG_ARCH_HAS_KPKEYS */ +#ifdef CONFIG_KPKEYS_HARDENED_PGTABLES + +DECLARE_STATIC_KEY_FALSE(kpkeys_hardened_pgtables_key); + +static inline bool kpkeys_hardened_pgtables_enabled(void) +{ + return static_branch_unlikely(&kpkeys_hardened_pgtables_key); +} + +static inline bool kpkeys_hardened_pgtables_early_enabled(void) +{ + return arch_supports_kpkeys_early(); +} + +/* + * Should be called from mem_init(): as soon as the buddy allocator becomes + * available and before any call to pagetable_alloc(). + */ +void kpkeys_hardened_pgtables_init(void); + +#else /* CONFIG_KPKEYS_HARDENED_PGTABLES */ + +static inline bool kpkeys_hardened_pgtables_enabled(void) +{ + return false; +} + +static inline bool kpkeys_hardened_pgtables_early_enabled(void) +{ + return false; +} + +static inline void kpkeys_hardened_pgtables_init(void) {} + +#endif /* CONFIG_KPKEYS_HARDENED_PGTABLES */ + #endif /* _LINUX_KPKEYS_H */ diff --git a/mm/Kconfig b/mm/Kconfig index 819fb0d7b7bd..042541d28692 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -1244,6 +1244,9 @@ config ARCH_HAS_PKEYS bool config ARCH_HAS_KPKEYS bool +config ARCH_HAS_KPKEYS_HARDENED_PGTABLES + bool + depends on ARCH_HAS_KPKEYS config ARCH_USES_PG_ARCH_2 bool diff --git a/mm/Makefile b/mm/Makefile index 8ad2ab08244e..7603e6051afa 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -150,3 +150,4 @@ obj-$(CONFIG_SHRINKER_DEBUG) += shrinker_debug.o obj-$(CONFIG_EXECMEM) += execmem.o obj-$(CONFIG_TMPFS_QUOTA) += shmem_quota.o obj-$(CONFIG_LAZY_MMU_MODE_KUNIT_TEST) += tests/lazy_mmu_mode_kunit.o +obj-$(CONFIG_KPKEYS_HARDENED_PGTABLES) += kpkeys_hardened_pgtables.o diff --git a/mm/kpkeys_hardened_pgtables.c b/mm/kpkeys_hardened_pgtables.c new file mode 100644 index 000000000000..763f267bbfe4 --- /dev/null +++ b/mm/kpkeys_hardened_pgtables.c @@ -0,0 +1,16 @@ +// SPDX-License-Identifier: GPL-2.0-only +#include +#include + +#include + +__ro_after_init DEFINE_STATIC_KEY_FALSE(kpkeys_hardened_pgtables_key); +EXPORT_SYMBOL_IF_KUNIT(kpkeys_hardened_pgtables_key); + +void __init kpkeys_hardened_pgtables_init(void) +{ + if (!kpkeys_enabled()) + return; + + static_branch_enable(&kpkeys_hardened_pgtables_key); +} diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening index 86f8768c63d4..fdaf977d4626 100644 --- a/security/Kconfig.hardening +++ b/security/Kconfig.hardening @@ -275,6 +275,18 @@ config BUG_ON_DATA_CORRUPTION If unsure, say N. +config KPKEYS_HARDENED_PGTABLES + bool "Harden page tables using kernel pkeys" + depends on ARCH_HAS_KPKEYS_HARDENED_PGTABLES + help + This option makes all page tables mostly read-only by + allocating them with a non-default protection key (pkey) and + only enabling write access to that pkey in routines that are + expected to write to page table entries. + + This option has no effect if the system does not support + kernel pkeys. + endmenu config CC_HAS_RANDSTRUCT -- 2.51.2