From nobody Tue Apr 7 19:54:16 2026 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 935B336A008; Fri, 27 Feb 2026 17:57:50 +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=1772215074; cv=none; b=sLMoCJPkaJ0O/J9O7rnmacjcG3lXgp2rIZ0b3f0ZgsXtRSamYmd3YUnozlNnsrqpomUS1WPUBniDl2RPixHmTnIVXBUKh+jqaG8cKswjyXuPFo+uVQxalzNRVL0aqMY5x7cYoCxD6GgCpPAMQnptSTn7M43sc3WGUfYdYuu9gKM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772215074; c=relaxed/simple; bh=9KwLUMHfMbYG//pAcS+P4qp3v8orqOpTxgyzlL2JBG8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=OHPgSEJS+7m0XPxq+UFGY4agq9kyJvm5JNbsxcmeuW4OCT6UgoBjUgHq82Mstj2wvV+v7/dElDU3Id7PWixvD/aHnV4vWK8wvSlaKq5Nd4HMvbfqGhcuWBziJr/RkO+ueOM0hFywzU42niKVn0RWG2E8zD+zphly9ZQeJSeriAY= 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 D969F1516; Fri, 27 Feb 2026 09:57:43 -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 C7D9C3F73B; Fri, 27 Feb 2026 09:57:45 -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 27/30] arm64: kpkeys: Guard page table writes Date: Fri, 27 Feb 2026 17:55:15 +0000 Message-ID: <20260227175518.3728055-28-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" When CONFIG_KPKEYS_HARDENED_PGTABLES is enabled, page tables (both user and kernel) are mapped with a privileged pkey in the linear mapping. As a result, they can only be written at an elevated kpkeys level. Introduce a kpkeys guard that sets POR_EL1 appropriately to allow writing to page tables, and use this guard wherever necessary. The scope is kept as small as possible, so that POR_EL1 is quickly reset to its default value. Where atomics are involved, the guard's scope encompasses the whole loop to avoid switching POR_EL1 unnecessarily. This patch is a no-op if CONFIG_KPKEYS_HARDENED_PGTABLES is disabled (default). Signed-off-by: Kevin Brodsky --- arch/arm64/include/asm/pgtable.h | 22 +++++++++++++++++++++- arch/arm64/mm/fault.c | 2 ++ 2 files changed, 23 insertions(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgta= ble.h index b3e58735c49b..8c85e23223da 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -39,6 +39,14 @@ #include #include #include +#include + +#ifdef CONFIG_KPKEYS_HARDENED_PGTABLES +KPKEYS_GUARD_COND(kpkeys_hardened_pgtables, KPKEYS_LVL_PGTABLES, + kpkeys_hardened_pgtables_enabled()) +#else +KPKEYS_GUARD_NOOP(kpkeys_hardened_pgtables) +#endif =20 static inline void emit_pte_barriers(void) { @@ -363,6 +371,7 @@ static inline pte_t pte_clear_uffd_wp(pte_t pte) =20 static inline void __set_pte_nosync(pte_t *ptep, pte_t pte) { + guard(kpkeys_hardened_pgtables)(); WRITE_ONCE(*ptep, pte); } =20 @@ -830,6 +839,7 @@ static inline void set_pmd(pmd_t *pmdp, pmd_t pmd) } #endif /* __PAGETABLE_PMD_FOLDED */ =20 + guard(kpkeys_hardened_pgtables)(); WRITE_ONCE(*pmdp, pmd); =20 if (pmd_valid(pmd)) @@ -890,6 +900,7 @@ static inline void set_pud(pud_t *pudp, pud_t pud) return; } =20 + guard(kpkeys_hardened_pgtables)(); WRITE_ONCE(*pudp, pud); =20 if (pud_valid(pud)) @@ -971,6 +982,7 @@ static inline void set_p4d(p4d_t *p4dp, p4d_t p4d) return; } =20 + guard(kpkeys_hardened_pgtables)(); WRITE_ONCE(*p4dp, p4d); queue_pte_barriers(); } @@ -1099,6 +1111,7 @@ static inline void set_pgd(pgd_t *pgdp, pgd_t pgd) return; } =20 + guard(kpkeys_hardened_pgtables)(); WRITE_ONCE(*pgdp, pgd); queue_pte_barriers(); } @@ -1295,6 +1308,7 @@ static inline int __ptep_test_and_clear_young(struct = vm_area_struct *vma, { pte_t old_pte, pte; =20 + guard(kpkeys_hardened_pgtables)(); pte =3D __ptep_get(ptep); do { old_pte =3D pte; @@ -1343,7 +1357,10 @@ static inline pte_t __ptep_get_and_clear_anysz(struc= t mm_struct *mm, pte_t *ptep, unsigned long pgsize) { - pte_t pte =3D __pte(xchg_relaxed(&pte_val(*ptep), 0)); + pte_t pte; + + scoped_guard(kpkeys_hardened_pgtables) + pte =3D __pte(xchg_relaxed(&pte_val(*ptep), 0)); =20 switch (pgsize) { case PAGE_SIZE: @@ -1416,6 +1433,7 @@ static inline void ___ptep_set_wrprotect(struct mm_st= ruct *mm, { pte_t old_pte; =20 + guard(kpkeys_hardened_pgtables)(); do { old_pte =3D pte; pte =3D pte_wrprotect(pte); @@ -1449,6 +1467,7 @@ static inline void __clear_young_dirty_pte(struct vm_= area_struct *vma, { pte_t old_pte; =20 + guard(kpkeys_hardened_pgtables)(); do { old_pte =3D pte; =20 @@ -1496,6 +1515,7 @@ static inline pmd_t pmdp_establish(struct vm_area_str= uct *vma, unsigned long address, pmd_t *pmdp, pmd_t pmd) { page_table_check_pmd_set(vma->vm_mm, address, pmdp, pmd); + guard(kpkeys_hardened_pgtables)(); return __pmd(xchg_relaxed(&pmd_val(*pmdp), pmd_val(pmd))); } #endif diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index be9dab2c7d6a..7e230499f7fe 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -214,6 +214,8 @@ int __ptep_set_access_flags(struct vm_area_struct *vma, if (pte_same(pte, entry)) return 0; =20 + guard(kpkeys_hardened_pgtables)(); + /* only preserve the access flags and write permission */ pte_val(entry) &=3D PTE_RDONLY | PTE_AF | PTE_WRITE | PTE_DIRTY; =20 --=20 2.51.2