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bh=tZCx6H+R2YFZA0lLWiMZtQV/Hy+U8ncgFSxFQ23UdqA=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=tIsYUIRX9NUSaLkDiVL/frOEpjOraO7b7Ujw8E9/8sWJlXOsVRfBRvlEPIKKy5/2b OX9i78F7MPbzP/Em2u8IG4oCPnQyJvZ5CSybZbzV6WLA79X4pz6pwrNcT082n/FI+U Aure/5nAHyQLFM2CQIQSCV97xfifLfU1yiwz68yI= From: Kevin Brodsky Date: Tue, 18 Aug 2026 15:08:54 +0100 Subject: [PATCH RFC v9 12/25] mm: kpkeys: Protect regular page tables MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260818-kpkeys-v9-12-743ad31b2c8f@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=5188; i=kevin.brodsky@arm.com; s=20260427; h=from:subject:message-id; bh=tZCx6H+R2YFZA0lLWiMZtQV/Hy+U8ncgFSxFQ23UdqA=; b=+wzJO/yKNtQkrrxtuiAwZr6RGyNqWmeattGueL0R06BjBBkuM3tkUp27om/GuO+f86HfknPmK gUvv1ntSCNYDJhr4LhiUi0N4i2pDOR7HO3lJUSyIGADw1unJGF+gEjl X-Developer-Key: i=kevin.brodsky@arm.com; a=ed25519; pk=N2QG+eJKrvkNovwhhwJhnJ4+ScVfsGCHldmqLfcMTFs= X-Rspamd-Queue-Id: 92A4F2000A X-Stat-Signature: d7jo7dn7bxb495fab5r8q5es3pfs8gh3 X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1787062342-660456 X-HE-Meta: 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 Z/9mR2oQ +9MzSF9q3HrruSE83CGhECrz3hEeG9+1q0SxS+SNZBhS/IieexShhWhRnIqdcpK2C0UKEl0BPF3axn/hdOsm0If+YIhok6RDMU1KQcGiLF/pRrAnV1ttvp6awFKVkKuCgviccRbAUv7qjV73tDQpMNvPMe7dCEePdtuopddGmourEa1UYLJ5JtRgR88R1rmES06WDdGsxzsZeD+Ocjrgfq3VTJWJyDerJpwbU1PJZwxiZjvUEgepw7VYL2E2sbM3Wp/OM Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: If the kpkeys_hardened_pgtables feature is enabled, page table pages (PTPs) should be protected by modifying the linear mapping to map them with a privileged pkey (KPKEYS_PKEY_PGTABLES). This patch introduces a new page allocator for that purpose: * kpkeys_pgtable_alloc() allocates a new PTP and sets the linear mapping to KPKEYS_PKEY_PGTABLES for that page * kpkeys_pgtable_free() frees such a PTP and restores the linear mapping to the default pkey This interface is then hooked into pagetable_alloc() and pagetable_free(), protecting all page tables created once the buddy allocator is available. Early page tables are allocated in other ways and will be protected in subsequent patches. This implementation of kpkeys_pgtable_{alloc,free}() is minimal and relies on the linear map being fully PTE-mapped - otherwise calling set_memory_pkey() on a single page may result in splitting a block mapping, which in turn requires allocating a new PTP. A more elaborate implementation could be added later to handle this situation. Signed-off-by: Kevin Brodsky --- include/linux/kpkeys.h | 10 +++++++++ include/linux/mm.h | 14 +++++++++++-- mm/kpkeys_hardened_pgtables.c | 47 +++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 69 insertions(+), 2 deletions(-) diff --git a/include/linux/kpkeys.h b/include/linux/kpkeys.h index 23ae4ed512f5..288c8853eed6 100644 --- a/include/linux/kpkeys.h +++ b/include/linux/kpkeys.h @@ -116,6 +116,9 @@ static inline bool kpkeys_hardened_pgtables_early_enabled(void) return arch_supports_kpkeys_early(); } +struct page *kpkeys_pgtable_alloc(gfp_t gfp, unsigned int order); +void kpkeys_pgtable_free(struct page *page, unsigned int order); + /* * Should be called from mem_init(): as soon as the buddy allocator becomes * available and before any call to pagetable_alloc(). @@ -134,6 +137,13 @@ static inline bool kpkeys_hardened_pgtables_early_enabled(void) return false; } +static inline struct page *kpkeys_pgtable_alloc(gfp_t gfp, unsigned int order) +{ + return NULL; +} + +static inline void kpkeys_pgtable_free(struct page *page, unsigned int order) {} + static inline void kpkeys_hardened_pgtables_init(void) {} #endif /* CONFIG_KPKEYS_HARDENED_PGTABLES */ diff --git a/include/linux/mm.h b/include/linux/mm.h index 485df9c2dbdd..eea3131786b3 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -37,6 +37,7 @@ #include #include #include +#include struct mempolicy; struct anon_vma; @@ -3682,7 +3683,12 @@ static inline bool ptdesc_test_kernel(const struct ptdesc *ptdesc) */ static inline struct ptdesc *pagetable_alloc_noprof(gfp_t gfp, unsigned int order) { - struct page *page = alloc_pages_noprof(gfp | __GFP_COMP, order); + struct page *page; + + if (kpkeys_hardened_pgtables_enabled()) + page = kpkeys_pgtable_alloc(gfp | __GFP_COMP, order); + else + page = alloc_pages_noprof(gfp | __GFP_COMP, order); return page_ptdesc(page); } @@ -3691,8 +3697,12 @@ static inline struct ptdesc *pagetable_alloc_noprof(gfp_t gfp, unsigned int orde static inline void __pagetable_free(struct ptdesc *pt) { struct page *page = ptdesc_page(pt); + unsigned int order = compound_order(page); - __free_pages(page, compound_order(page)); + if (kpkeys_hardened_pgtables_enabled()) + kpkeys_pgtable_free(page, order); + else + __free_pages(page, order); } #ifdef CONFIG_ASYNC_KERNEL_PGTABLE_FREE diff --git a/mm/kpkeys_hardened_pgtables.c b/mm/kpkeys_hardened_pgtables.c index 4c654e0cf585..eca798207107 100644 --- a/mm/kpkeys_hardened_pgtables.c +++ b/mm/kpkeys_hardened_pgtables.c @@ -1,12 +1,59 @@ // SPDX-License-Identifier: GPL-2.0-only #include #include +#include #include __ro_after_init DEFINE_STATIC_KEY_FALSE(kpkeys_hardened_pgtables_key); EXPORT_SYMBOL_IF_KUNIT(kpkeys_hardened_pgtables_key); +static int set_pkey_pgtable(struct page *page, unsigned int nr_pages) +{ + unsigned long addr = (unsigned long)page_address(page); + int ret; + + ret = set_memory_pkey(addr, nr_pages, KPKEYS_PKEY_PGTABLES); + + WARN_ON(ret); + return ret; +} + +static int set_pkey_default(struct page *page, unsigned int nr_pages) +{ + unsigned long addr = (unsigned long)page_address(page); + int ret; + + ret = set_memory_pkey(addr, nr_pages, 0); + + WARN_ON(ret); + return ret; +} + +struct page *kpkeys_pgtable_alloc(gfp_t gfp, unsigned int order) +{ + struct page *page; + int ret; + + page = alloc_pages_noprof(gfp, order); + if (!page) + return page; + + ret = set_pkey_pgtable(page, 1 << order); + if (ret) { + __free_pages(page, order); + return NULL; + } + + return page; +} + +void kpkeys_pgtable_free(struct page *page, unsigned int order) +{ + set_pkey_default(page, 1 << order); + __free_pages(page, order); +} + void __init kpkeys_hardened_pgtables_init(void) { if (!kpkeys_supported()) -- 2.51.2