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h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=Yu3zLptzCPLqvH8Q+sqa85JAVjpLwPQbG+OrPDX/KS8hogd41ekg7h6crakPjmpTP Ku9IYp3fgjgPyxdJNPDSBF8daqF1TwN29q45z9YMD/uBuVQz7gAeTh6JYGL+Nv70LQ G4Sp3UZIpY0k6OvcGBMLg4rsfaNYhxFbPLZEUqfc= From: Kevin Brodsky Date: Tue, 05 May 2026 17:06:10 +0100 Subject: [PATCH RFC v7 21/24] arm64: kpkeys: Guard page table writes MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260505-kpkeys-v7-21-20c0bdd97197@arm.com> References: <20260505-kpkeys-v7-0-20c0bdd97197@arm.com> In-Reply-To: <20260505-kpkeys-v7-0-20c0bdd97197@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 , Will Deacon , Yang Shi , Yeoreum Yun , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, x86@kernel.org, Lorenzo Stoakes , Thomas Gleixner , Vlastimil Babka X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=ed25519-sha256; t=1777997220; l=4227; i=kevin.brodsky@arm.com; s=20260427; h=from:subject:message-id; bh=EySxOil8TcwYwuEGrwoYGjRX1REQ6GfG8Z5Pa273DNk=; b=mRcytsacp6RNX+Hj6r9mKLTM3GOBVXID2ixTkPwGAnuh7HX9DpNNqWA8cg4SGJhhJl7bEh0zm 1Jw6+Pn/60MCHN6q6Oe4v/RN3AvQYzLlIvhzlxWAB1KFdXTIH/hF8uY X-Developer-Key: i=kevin.brodsky@arm.com; a=ed25519; pk=N2QG+eJKrvkNovwhhwJhnJ4+ScVfsGCHldmqLfcMTFs= X-Stat-Signature: g853rq64j1uez3q8mfsppzkrgremn876 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 3155340016 X-Rspam-User: X-HE-Tag: 1777997318-130717 X-HE-Meta: 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 aQzR9x+O 1SrZcFQr/7Av/exzcdgTJqtN/pCVnL230rqDyTgESVpW2uaZUh40czadD6UTUoEfEANoXEinm2RLCVKUR+Kb6hI6s9GhQb7qzdL7BjpBs0VdD19SCTmWPjnqa05UfPD/huBTZV6BIio93uw147LR7Qtim1OTo1wltgm77rmXQdqsE34/WXc2muUIoLOgpNXN47s9EXaUafkEhwfm8FsWv9iYZDRiWYGwPYE+E1L6AqUYwYQp7eVO6IkP9TIelA/GLMwYO5PuJC1bSO/k2G5dJCMBxnKH+OEKa1iUfkEyELadVvyluhk+8tUlcUJRoMcU+b3cOvwy1M23pSsc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 in a privileged kpkeys context. 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/pgtable.h index 4dfa42b7d053..20072f32677d 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_CTX_PGTABLES, + kpkeys_hardened_pgtables_enabled()) +#else +KPKEYS_GUARD_NOOP(kpkeys_hardened_pgtables) +#endif static inline void emit_pte_barriers(void) { @@ -359,6 +367,7 @@ static inline pte_t pte_clear_uffd_wp(pte_t pte) static inline void __set_pte_nosync(pte_t *ptep, pte_t pte) { + guard(kpkeys_hardened_pgtables)(); WRITE_ONCE(*ptep, pte); } @@ -830,6 +839,7 @@ static inline void set_pmd(pmd_t *pmdp, pmd_t pmd) } #endif /* __PAGETABLE_PMD_FOLDED */ + guard(kpkeys_hardened_pgtables)(); WRITE_ONCE(*pmdp, pmd); if (pmd_valid(pmd)) @@ -894,6 +904,7 @@ static inline void set_pud(pud_t *pudp, pud_t pud) return; } + guard(kpkeys_hardened_pgtables)(); WRITE_ONCE(*pudp, pud); if (pud_valid(pud)) @@ -975,6 +986,7 @@ static inline void set_p4d(p4d_t *p4dp, p4d_t p4d) return; } + guard(kpkeys_hardened_pgtables)(); WRITE_ONCE(*p4dp, p4d); queue_pte_barriers(); } @@ -1103,6 +1115,7 @@ static inline void set_pgd(pgd_t *pgdp, pgd_t pgd) return; } + guard(kpkeys_hardened_pgtables)(); WRITE_ONCE(*pgdp, pgd); queue_pte_barriers(); } @@ -1307,6 +1320,7 @@ static inline bool __ptep_test_and_clear_young(struct vm_area_struct *vma, { pte_t old_pte, pte; + guard(kpkeys_hardened_pgtables)(); pte = __ptep_get(ptep); do { old_pte = pte; @@ -1354,7 +1368,10 @@ static inline pte_t __ptep_get_and_clear_anysz(struct mm_struct *mm, pte_t *ptep, unsigned long pgsize) { - pte_t pte = __pte(xchg_relaxed(&pte_val(*ptep), 0)); + pte_t pte; + + scoped_guard(kpkeys_hardened_pgtables) + pte = __pte(xchg_relaxed(&pte_val(*ptep), 0)); switch (pgsize) { case PAGE_SIZE: @@ -1427,6 +1444,7 @@ static inline void ___ptep_set_wrprotect(struct mm_struct *mm, { pte_t old_pte; + guard(kpkeys_hardened_pgtables)(); do { old_pte = pte; pte = pte_wrprotect(pte); @@ -1460,6 +1478,7 @@ static inline void __clear_young_dirty_pte(struct vm_area_struct *vma, { pte_t old_pte; + guard(kpkeys_hardened_pgtables)(); do { old_pte = pte; @@ -1507,6 +1526,7 @@ static inline pmd_t pmdp_establish(struct vm_area_struct *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 0f3c5c7ca054..858f5d3e8f22 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -216,6 +216,8 @@ int __ptep_set_access_flags_anysz(struct vm_area_struct *vma, if (pte_same(pte, entry)) return 0; + guard(kpkeys_hardened_pgtables)(); + /* only preserve the access flags and write permission */ pte_val(entry) &= PTE_RDONLY | PTE_AF | PTE_WRITE | PTE_DIRTY; -- 2.51.2