From nobody Tue Apr 7 19:54:15 2026 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 21DA3363C47; Fri, 27 Feb 2026 17:56:44 +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=1772215006; cv=none; b=OtLhYpY1kO79fOAi6OIRdyy4Jwmi5yEsSCGmDIcIbx1AZmMGtJgX7DAtYp6O8aMt4O1sAjKBgV2jiA/bKW7q+XiNPNVkgIdikK1YvNJf3/Pe5qozUi4vGWk+jE0rBOLZuzR8TQnsaPDhQ2jK4A4/afu5Z3McmsYp6HVg4EJMXOA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772215006; c=relaxed/simple; bh=D5Owso3kL3tNXX+NEVCNUdCgiZjSrcpI+oWpSvO/QiM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=c11M8GtFO+LMD5Vp2xgYC6b+xqnvzrEn82jYaV83omdYf69oMk4javYcbPp+inB08QP46e9Vz1XtOHMWqCZnJXPeYccHrKmtdvsye68dtpq0cEuPZmOqZxnDfgWInEZ0OVMejpGmhRL8wkgibEi3xkyQAhVrH2Os6Z7zkB1GPBk= 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; 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 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 3F377176B; Fri, 27 Feb 2026 09:56:38 -0800 (PST) Received: from e123572-lin.arm.com (e123572-lin.cambridge.arm.com [10.1.194.54]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 2979F3F73B; Fri, 27 Feb 2026 09:56:40 -0800 (PST) From: Kevin Brodsky To: linux-hardening@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Kevin Brodsky , Andrew Morton , Andy Lutomirski , Catalin Marinas , Dave Hansen , David Hildenbrand , Ira Weiny , Jann Horn , Jeff Xu , Joey Gouly , Kees Cook , Linus Walleij , Lorenzo Stoakes , Marc Zyngier , Mark Brown , Matthew Wilcox , Maxwell Bland , "Mike Rapoport (IBM)" , Peter Zijlstra , Pierre Langlois , Quentin Perret , Rick Edgecombe , Ryan Roberts , Thomas Gleixner , Vlastimil Babka , Will Deacon , Yang Shi , Yeoreum Yun , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, x86@kernel.org Subject: [PATCH v6 13/30] mm: kpkeys: Introduce kpkeys_hardened_pgtables feature Date: Fri, 27 Feb 2026 17:55:01 +0000 Message-ID: <20260227175518.3728055-14-kevin.brodsky@arm.com> X-Mailer: git-send-email 2.51.2 In-Reply-To: <20260227175518.3728055-1-kevin.brodsky@arm.com> References: <20260227175518.3728055-1-kevin.brodsky@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 a higher kpkeys level (KPKEYS_LVL_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. Signed-off-by: Kevin Brodsky --- include/asm-generic/kpkeys.h | 4 ++++ include/linux/kpkeys.h | 30 +++++++++++++++++++++++++++++- mm/Kconfig | 3 +++ mm/Makefile | 1 + mm/kpkeys_hardened_pgtables.c | 13 +++++++++++++ security/Kconfig.hardening | 12 ++++++++++++ 6 files changed, 62 insertions(+), 1 deletion(-) create mode 100644 mm/kpkeys_hardened_pgtables.c 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 =20 +#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 faa6e2615798..49af2ec76923 100644 --- a/include/linux/kpkeys.h +++ b/include/linux/kpkeys.h @@ -4,11 +4,13 @@ =20 #include #include +#include =20 #define KPKEYS_LVL_DEFAULT 0 +#define KPKEYS_LVL_PGTABLES 1 =20 #define KPKEYS_LVL_MIN KPKEYS_LVL_DEFAULT -#define KPKEYS_LVL_MAX KPKEYS_LVL_DEFAULT +#define KPKEYS_LVL_MAX KPKEYS_LVL_PGTABLES =20 #define __KPKEYS_GUARD(name, set_level, restore_pkey_reg, set_arg, ...) \ __DEFINE_CLASS_IS_CONDITIONAL(name, false); \ @@ -110,4 +112,30 @@ static inline bool arch_kpkeys_enabled(void) =20 #endif /* CONFIG_ARCH_HAS_KPKEYS */ =20 +#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); +} + +/* + * 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 void kpkeys_hardened_pgtables_init(void) {} + +#endif /* CONFIG_KPKEYS_HARDENED_PGTABLES */ + #endif /* _LINUX_KPKEYS_H */ diff --git a/mm/Kconfig b/mm/Kconfig index 2baedee59bb2..2f87ee69d16e 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -1245,6 +1245,9 @@ config ARCH_HAS_PKEYS bool config ARCH_HAS_KPKEYS bool +# ARCH_HAS_KPKEYS must be selected when selecting this option +config ARCH_HAS_KPKEYS_HARDENED_PGTABLES + bool =20 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-$(CONFIG_SHRINKER_DEBUG) +=3D shrinker_debug.o obj-$(CONFIG_EXECMEM) +=3D execmem.o obj-$(CONFIG_TMPFS_QUOTA) +=3D shmem_quota.o obj-$(CONFIG_LAZY_MMU_MODE_KUNIT_TEST) +=3D tests/lazy_mmu_mode_kunit.o +obj-$(CONFIG_KPKEYS_HARDENED_PGTABLES) +=3D kpkeys_hardened_pgtables.o diff --git a/mm/kpkeys_hardened_pgtables.c b/mm/kpkeys_hardened_pgtables.c new file mode 100644 index 000000000000..9e4771263ad2 --- /dev/null +++ b/mm/kpkeys_hardened_pgtables.c @@ -0,0 +1,13 @@ +// SPDX-License-Identifier: GPL-2.0-only +#include +#include + +__ro_after_init DEFINE_STATIC_KEY_FALSE(kpkeys_hardened_pgtables_key); + +void __init kpkeys_hardened_pgtables_init(void) +{ + if (!arch_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 =20 If unsure, say N. =20 +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 =20 config CC_HAS_RANDSTRUCT --=20 2.51.2