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bh=6UbRYk/YvXUAWtpLYZu6wDPS/Pd5/nUfgqkLWHxrJ7c=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=PePxMqzVehj2UIBIbvm64QPCtnTfHakL0X6eYCYG5J1vb7mX7Z/Psv1CjxGeS/4QO IsEBBZDmeJFpvUK/kTgDkv3PDWQbzu8JWM8A0PpE16sxAkCdbkmo/xXA9mCxO7cLv0 DMI3tXJJzIrziKlnKHRV0juOFlczSPj0yPtA3hhg= From: Kevin Brodsky Date: Tue, 26 May 2026 12:16:01 +0100 Subject: [PATCH RFC v8 12/24] mm: kpkeys: Protect regular page tables MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260526-kpkeys-v8-12-eaaacdacc67c@arm.com> References: <20260526-kpkeys-v8-0-eaaacdacc67c@arm.com> In-Reply-To: <20260526-kpkeys-v8-0-eaaacdacc67c@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 , Vlastimil Babka , Will Deacon , Yang Shi , Yeoreum Yun , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, x86@kernel.org, Lorenzo Stoakes , Thomas Gleixner X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=ed25519-sha256; t=1779794212; l=5204; i=kevin.brodsky@arm.com; s=20260427; h=from:subject:message-id; bh=6UbRYk/YvXUAWtpLYZu6wDPS/Pd5/nUfgqkLWHxrJ7c=; b=AfN7/YEevro//gMjkeXy1J5hlaMTGq9n0DUXKz40Zk4xYFsOdqkZJNxCNaiTUVJj9XCfiB7uO IVqsUweiiGOD1AQZhV/Z19fptOVNk7FpYunOkPfOIhc3Pm70S4uyOt0 X-Developer-Key: i=kevin.brodsky@arm.com; a=ed25519; pk=N2QG+eJKrvkNovwhhwJhnJ4+ScVfsGCHldmqLfcMTFs= X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: B9DD4180009 X-Stat-Signature: iotpmdeqp77t8y3ysajihw67egmeahri X-HE-Tag: 1779794280-577357 X-HE-Meta: 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 yFcqrxAN 5JRTDiFJW2hizDapjeyI0KRfdZkxYJi/NYLqteZFToOBTXV29jXbhT6TYmhz4tj/6okYfRhtz0uQbBzzZjXdPIbetrgNnV//rKjOJNlIixyp6MSdh7ABOdL3AHGt16svEVxb+8ex7L4wMNqw4ytfkp9wlsPsF9Xu3dR3ljGRwtfrNIgKWkx0XnUXBdXHBVPvwFx9PTGIn9StVd7J643zVrS3f+sPfMzZTaz70bhZvVxZ4Q3l2P6KR/yZc7NeIUdQ2JsYyd+9HJyZpXxGOLOK9y0t9o+BC0Cbt6BFp 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 d413a17f8882..c7529f9e9f97 100644 --- a/include/linux/kpkeys.h +++ b/include/linux/kpkeys.h @@ -135,6 +135,9 @@ 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(). @@ -153,6 +156,13 @@ 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 af23453e9dbd..7b95b2351763 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -37,6 +37,7 @@ #include #include #include +#include struct mempolicy; struct anon_vma; @@ -3648,7 +3649,12 @@ 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); } @@ -3657,8 +3663,12 @@ 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 763f267bbfe4..fff7e2a64b64 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, KPKEYS_PKEY_DEFAULT); + + 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_enabled()) -- 2.51.2