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a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1787062336; bh=/3l8zOUYVj+WOkd0xAlju+IzOxqp5kEU0RRVT0zZ9Bw=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=DijChpUdF1RuBdkyLFATeOsiSAmz3vRvsbQu9Xf4r8fSCwkLPYeX2u4TqhHmuvK5v bEA78LX2fa1R1gpIgUtzR5f05+sSjB9A7FnAX66ViZQxIp8GFqGwo92X07hrUbqCmL RxLHMp+W+M6Qq0IWBi4KLPfjUbXSDVaC+IE4DK+w= From: Kevin Brodsky Date: Tue, 18 Aug 2026 15:08:53 +0100 Subject: [PATCH RFC v9 11/25] mm: kpkeys: Introduce kpkeys_hardened_pgtables feature MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260818-kpkeys-v9-11-743ad31b2c8f@arm.com> References: <20260818-kpkeys-v9-0-743ad31b2c8f@arm.com> In-Reply-To: <20260818-kpkeys-v9-0-743ad31b2c8f@arm.com> To: linux-hardening@vger.kernel.org Cc: Kevin Brodsky , Andrew Morton , Andy Lutomirski , Catalin Marinas , Dave Hansen , "David Hildenbrand (Arm)" , Jann Horn , Jeff Xu , Joey Gouly , Kees Cook , Linu Cherian , Linus Walleij , Marc Zyngier , Mark Brown , Matthew Wilcox , Maxwell Bland , "Mike Rapoport (IBM)" , Peter Zijlstra , Pierre Langlois , =?utf-8?q?Pierre-Cl=C3=A9ment_Tosi?= , 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, Ira Weiny , Lorenzo Stoakes , Thomas Gleixner X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=ed25519-sha256; t=1787062276; l=5593; i=kevin.brodsky@arm.com; s=20260427; h=from:subject:message-id; bh=/3l8zOUYVj+WOkd0xAlju+IzOxqp5kEU0RRVT0zZ9Bw=; b=qTIS+Q2f7O/ftDpgcOtYPcie0+ZP70DESK0YuE6VZ35VxabKw7HIm6ZYoMNyRRP8plVUnpJTj ukEN7bDubSeA5X5+HECw13im2U5oHjzFkg4rQuW3Ysw2V1t7wzyGZku X-Developer-Key: i=kevin.brodsky@arm.com; a=ed25519; pk=N2QG+eJKrvkNovwhhwJhnJ4+ScVfsGCHldmqLfcMTFs= X-Rspamd-Queue-Id: 8C1D91C0006 X-Rspam-User: X-Stat-Signature: qom57xnedd1upyihzgh89qb8r4wqs7mb X-Rspamd-Server: rspam06 X-HE-Tag: 1787062337-863189 X-HE-Meta: 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 Enx5ZzaN 7XHCp4oXkBr3Dpd101wS/pSBpSha3Gh6dluneHdQrv2PQHd9wKZ7acuch0XqqkhPYksdITxs47a24sCtRFe5QrNKy2+XfSftoQsqBWQFHM07xbbaeGzfp4BLabAdEcvlbxfXkGmEJ5uQDOCPvrAiGMhzl6WahpX3/t50yEyUOcLiFbHxofUd1fAD5Z/yoRxRa3ZxRxCYatDDbGdYKD7t10j82dJcjEbdd5848nRXku4xIsOPqWyk2Tf9QE1sngT7asKqylcpC4aULSikAoj7Sjq3KjiM2gF3NKELmXR/77YK19VHac7FX+dk1/gY7HdLHe34qsyxEzn0v6Lekvd4VYAu5Rg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 supported 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/linux/kpkeys.h | 37 +++++++++++++++++++++++++++++++++++++ include/linux/kpkeys_types.h | 5 +++++ mm/Kconfig | 3 +++ mm/Makefile | 1 + mm/kpkeys_hardened_pgtables.c | 16 ++++++++++++++++ security/Kconfig.hardening | 12 ++++++++++++ 6 files changed, 74 insertions(+) diff --git a/include/linux/kpkeys.h b/include/linux/kpkeys.h index eac522f55214..23ae4ed512f5 100644 --- a/include/linux/kpkeys.h +++ b/include/linux/kpkeys.h @@ -4,6 +4,7 @@ #include #include +#include #include /** @@ -101,4 +102,40 @@ static inline bool kpkeys_supported(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/include/linux/kpkeys_types.h b/include/linux/kpkeys_types.h index 9de59092e9c3..09f15a9565cf 100644 --- a/include/linux/kpkeys_types.h +++ b/include/linux/kpkeys_types.h @@ -8,10 +8,15 @@ #include #endif +#ifndef KPKEYS_PKEY_PGTABLES +#define KPKEYS_PKEY_PGTABLES 1 +#endif + #if defined(CONFIG_ARCH_HAS_KPKEYS) && !defined(__ASSEMBLY__) enum kpkeys_ctx { KPKEYS_CTX_DEFAULT = 0, + KPKEYS_CTX_PGTABLES, KPKEYS_CTX_COUNT, }; diff --git a/mm/Kconfig b/mm/Kconfig index 55e6763d5792..21bd3e550de8 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -1283,6 +1283,9 @@ 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 eff9f9e7e061..35982b6efb56 100644 --- a/mm/Makefile +++ b/mm/Makefile @@ -147,3 +147,4 @@ 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..4c654e0cf585 --- /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_supported()) + return; + + static_branch_enable(&kpkeys_hardened_pgtables_key); +} diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening index 6923036e1a2f..bb75b580b7f1 100644 --- a/security/Kconfig.hardening +++ b/security/Kconfig.hardening @@ -271,6 +271,18 @@ 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