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t=1777997278; bh=7pzU3b7DWaYhX0sffzNlwFRd/XRrt+LdkFDa48ecpjg=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=cBR/6v4Hv4Sr3C+f8YDgEMZpwRWX1wtvmFmvJ4Q2erUf2USp4d9GAswyqWIF4sbnG GLczzGyxydeIfR6a0yyGKRWCwOyymK1qljTki04APrLxiztckPYDhTly8QWWwWVkWp T9E7LuRUPGl4uZfQnqobNvCfJI5rRz0OdpVFUCK8= From: Kevin Brodsky Date: Tue, 05 May 2026 17:06:01 +0100 Subject: [PATCH RFC v7 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: <20260505-kpkeys-v7-12-20c0bdd97197@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=5204; i=kevin.brodsky@arm.com; s=20260427; h=from:subject:message-id; bh=7pzU3b7DWaYhX0sffzNlwFRd/XRrt+LdkFDa48ecpjg=; b=gnCgSobzbTfSdcQyyWLGAZ1VLNECP5e8FFcomVkcQfwTIUG7UQTxpTJUfrmF0R9blBKBKk2dU 7NsCVzqmZ4hC2NzC38FxkayBoIYqxn8krJSXX+7okMc6XTHfLzpc8aQ X-Developer-Key: i=kevin.brodsky@arm.com; a=ed25519; pk=N2QG+eJKrvkNovwhhwJhnJ4+ScVfsGCHldmqLfcMTFs= X-Rspam-User: X-Rspamd-Queue-Id: 48FDA1A0019 X-Rspamd-Server: rspam04 X-Stat-Signature: ssj3wh3hbzdo371o9rhstsyqo95r6rnm X-HE-Tag: 1777997279-683009 X-HE-Meta: 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 +zaUpT7a EixGcXPt8/ETBEk0PZjYg8TcVnlOLiRGn3/eh2xKv4oh9UFSuwtVlmFv6Eb+356tjT+AvahFCXsyBPFZT8ErLY/JRdLzP43yZLhn6SEtnO8GljhhdTFqok6EY+RaTEAsdZmdJu8kOyAIxm9HT+Ribs2uZLUHuHK7LoOCfUp8bqbUMCGQwEnGXaQfn/sT1WAjIXEfmuUSVP/jmFah94IC3UD1N9SSj8ODvgY3E8sqppJKA1gBZvMJ3k/fCm9WoMR0zkMH7qTVLXmNc6bla7HGkZ4kad9PmRUWLxljF 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 1ed0299ad5ac..c9f63415162b 100644 --- a/include/linux/kpkeys.h +++ b/include/linux/kpkeys.h @@ -131,6 +131,9 @@ 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(). @@ -149,6 +152,13 @@ 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