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Tue, 01 Sep 2026 08:18:37 -0700 (PDT) From: Xueyuan Chen To: akpm@linux-foundation.org Cc: david@kernel.org, ljs@kernel.org, usama.arif@linux.dev, ziy@nvidia.com, baolin.wang@linux.alibaba.com, liam@infradead.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, kas@kernel.org, rppt@kernel.org, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, linux-arm-kernel@lists.infradead.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, luto@kernel.org, peterz@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v7 1/3] mm: make persistent huge zero folio read-only Date: Tue, 1 Sep 2026 23:18:16 +0800 Message-ID: <20260901151818.3191443-2-xueyuan.chen21@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260901151818.3191443-1-xueyuan.chen21@gmail.com> References: <20260901151818.3191443-1-xueyuan.chen21@gmail.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" The persistent huge zero folio is shared globally and should stay zero after initialization. As Jann Horn pointed out [1], kernel bugs have ended up writing to pages that were meant to be read-only, including in security-sensitive cases. Making the folio read-only in the direct map turns such writes into faults instead of silent zero-page corruption. Add a page-based helper consistent with the existing direct-map interfaces. Handle TLB invalidation in the architecture implementation; unsupported architectures retain their current behavior. Protect the folio after initialization. Skip highmem folios, which have no permanent direct-map mapping. Inspired by Jann Horn's read-only zero page work [1] and follow-up discussion [3] with Yang Shi. Link: https://lore.kernel.org/r/20260508-ro-zeropage-v1-1-9808abc20b49@goog= le.com [1] Link: https://lore.kernel.org/r/0e5b23a6-4895-454a-9dfa-6dc21adc2991@kernel= .org [2] Link: https://lore.kernel.org/r/CAHbLzkrXXe7r3n3jXgDKtwZhRqj=3DjDx9E6dLOULo= hnhBguvi9A@mail.gmail.com [3] Suggested-by: David Hildenbrand Suggested-by: Usama Arif Co-developed-by: Lance Yang Signed-off-by: Lance Yang Signed-off-by: Xueyuan Chen --- include/linux/set_memory.h | 17 +++++++++++++++++ mm/huge_memory.c | 13 ++++++++++--- 2 files changed, 27 insertions(+), 3 deletions(-) diff --git a/include/linux/set_memory.h b/include/linux/set_memory.h index 3fe293cfed8c..ed9ce04b18a1 100644 --- a/include/linux/set_memory.h +++ b/include/linux/set_memory.h @@ -54,6 +54,23 @@ static inline bool can_set_direct_map(void) #endif #endif /* CONFIG_ARCH_HAS_SET_DIRECT_MAP */ =20 +#ifndef set_direct_map_ro +/** + * set_direct_map_ro - make a direct-map range read-only + * @page: first page in the direct-map range + * @nr: number of pages in the range + * + * Make the direct-map range starting at @page read-only and invalidate st= ale + * writable translations before returning. + * + * Return: 0 on success, or a negative error code on failure. + */ +static inline int set_direct_map_ro(struct page *page, unsigned int nr) +{ + return 0; +} +#endif + #ifdef CONFIG_X86_64 int set_mce_nospec(unsigned long pfn); int clear_mce_nospec(unsigned long pfn); diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 54494c3fa983..742283b36d74 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -42,6 +42,7 @@ #include #include #include +#include =20 #include #include "internal.h" @@ -291,10 +292,16 @@ static int __init huge_zero_init(void) huge_zero_folio =3D alloc_huge_zero_folio(); if (!huge_zero_folio) { pr_warn("Allocating persistent huge zero folio failed\n"); - } else { - huge_zero_pfn =3D folio_pfn(huge_zero_folio); - count_vm_event(THP_ZERO_PAGE_ALLOC); + return 0; } + + huge_zero_pfn =3D folio_pfn(huge_zero_folio); + count_vm_event(THP_ZERO_PAGE_ALLOC); + + /* Highmem folios have no permanent direct-map mapping to protect. */ + if (!folio_test_highmem(huge_zero_folio)) + set_direct_map_ro(folio_page(huge_zero_folio, 0), HPAGE_PMD_NR); + return 0; } =20 --=20 2.47.3 From nobody Sat Sep 26 12:28:43 2026 Received: from mail-pf1-f171.google.com (mail-pf1-f171.google.com [209.85.210.171]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BE9D92D5C7A for ; 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charset="utf-8" Implement set_direct_map_ro() for arm64 and flush the TLB internally. Co-developed-by: Lance Yang Signed-off-by: Lance Yang Signed-off-by: Xueyuan Chen --- arch/arm64/include/asm/set_memory.h | 2 ++ arch/arm64/mm/pageattr.c | 12 ++++++++++++ 2 files changed, 14 insertions(+) diff --git a/arch/arm64/include/asm/set_memory.h b/arch/arm64/include/asm/s= et_memory.h index 0091ba12200e..1be86dc11543 100644 --- a/arch/arm64/include/asm/set_memory.h +++ b/arch/arm64/include/asm/set_memory.h @@ -13,6 +13,8 @@ int set_memory_valid(unsigned long addr, int numpages, in= t enable); =20 int set_direct_map_invalid_noflush(struct page *page, unsigned int numpage= s); int set_direct_map_default_noflush(struct page *page, unsigned int numpage= s); +int set_direct_map_ro(struct page *page, unsigned int nr); +#define set_direct_map_ro set_direct_map_ro bool kernel_page_present(struct page *page); =20 int set_memory_encrypted(unsigned long addr, int numpages); diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c index 132938b32eb1..0e95cd904ccb 100644 --- a/arch/arm64/mm/pageattr.c +++ b/arch/arm64/mm/pageattr.c @@ -355,6 +355,18 @@ int realm_register_memory_enc_ops(void) return arm64_mem_crypt_ops_register(&realm_crypt_ops); 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Tue, 01 Sep 2026 08:18:54 -0700 (PDT) Received: from o6.lan ([240e:391:ed0:47d0::1]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-85db24f33a0sm89911b3a.9.2026.09.01.08.18.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 01 Sep 2026 08:18:53 -0700 (PDT) From: Xueyuan Chen To: akpm@linux-foundation.org Cc: david@kernel.org, ljs@kernel.org, usama.arif@linux.dev, ziy@nvidia.com, baolin.wang@linux.alibaba.com, liam@infradead.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, kas@kernel.org, rppt@kernel.org, catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com, linux-arm-kernel@lists.infradead.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, luto@kernel.org, peterz@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v7 3/3] x86/mm: add set_direct_map_ro() Date: Tue, 1 Sep 2026 23:18:18 +0800 Message-ID: <20260901151818.3191443-4-xueyuan.chen21@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260901151818.3191443-1-xueyuan.chen21@gmail.com> References: <20260901151818.3191443-1-xueyuan.chen21@gmail.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" Implement set_direct_map_ro() for x86 with a page-based interface. Clear _PAGE_RW and _PAGE_DIRTY through the CPA path and let the common CPA wrapper invalidate stale writable translations before returning. Co-developed-by: Lance Yang Signed-off-by: Lance Yang Signed-off-by: Xueyuan Chen --- arch/x86/include/asm/set_memory.h | 2 ++ arch/x86/mm/pat/set_memory.c | 10 ++++++++++ 2 files changed, 12 insertions(+) diff --git a/arch/x86/include/asm/set_memory.h b/arch/x86/include/asm/set_m= emory.h index 39271a5ea925..710164ea8258 100644 --- a/arch/x86/include/asm/set_memory.h +++ b/arch/x86/include/asm/set_memory.h @@ -88,6 +88,8 @@ int set_pages_rw(struct page *page, int numpages); =20 int set_direct_map_invalid_noflush(struct page *page, unsigned int nr); int set_direct_map_default_noflush(struct page *page, unsigned int nr); +int set_direct_map_ro(struct page *page, unsigned int nr); +#define set_direct_map_ro set_direct_map_ro bool kernel_page_present(struct page *page); =20 extern int kernel_set_to_readonly; diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c index a1a061d995b3..7c0cfa7acd17 100644 --- a/arch/x86/mm/pat/set_memory.c +++ b/arch/x86/mm/pat/set_memory.c @@ -2666,6 +2666,16 @@ int set_direct_map_default_noflush(struct page *page= , unsigned int nr) return __set_pages_p(page, nr, 0); } =20 +int set_direct_map_ro(struct page *page, unsigned int nr) +{ + unsigned long addr =3D (unsigned long)page_address(page); + + /* Direct-map callers are expected to pass pages without aliases. */ + return change_page_attr_set_clr(&addr, nr, __pgprot(0), + __pgprot(_PAGE_RW | _PAGE_DIRTY), 0, + CPA_NO_CHECK_ALIAS, NULL); +} + #ifdef CONFIG_DEBUG_PAGEALLOC void __kernel_map_pages(struct page *page, int numpages, int enable) { --=20 2.47.3