[PATCH RFC v3 2/4] mm/pgtable: Make pfn_pte() filter out huge page attributes
From: Yin Tirui <hidden>
Date: 2026-02-28 07:15:27
Also in:
linux-mm, lkml
Subsystem:
arm64 port (aarch64 architecture), the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Catalin Marinas, Will Deacon, Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
A fundamental principle of page table type safety is that `pte_t` represents the lowest level page table entry and should never carry huge page attributes. Currently, passing a pgprot with huge page bits (e.g., extracted via pmd_pgprot()) into pfn_pte() creates a malformed PTE that retains the huge attribute, leading to the necessity of the ugly `pte_clrhuge()` anti-pattern. Enforce type safety by making `pfn_pte()` inherently filter out huge page attributes: - On x86: Strip the `_PAGE_PSE` bit. - On ARM64: Mask out the block descriptor bits in `PTE_TYPE_MASK` and enforce the `PTE_TYPE_PAGE` format. - On RISC-V: No changes required, as RISC-V leaf PMDs and PTEs share the exact same hardware format and do not use a distinct huge bit. Signed-off-by: Yin Tirui <redacted> --- arch/arm64/include/asm/pgtable.h | 4 +++- arch/x86/include/asm/pgtable.h | 4 ++++ 2 files changed, 7 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index b3e58735c49b..f2a7a40106d2 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h@@ -141,7 +141,9 @@ static inline pteval_t __phys_to_pte_val(phys_addr_t phys) #define pte_pfn(pte) (__pte_to_phys(pte) >> PAGE_SHIFT) #define pfn_pte(pfn,prot) \ - __pte(__phys_to_pte_val((phys_addr_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot)) + __pte(__phys_to_pte_val((phys_addr_t)(pfn) << PAGE_SHIFT) | \ + ((pgprot_val(prot) & ~(PTE_TYPE_MASK & ~PTE_VALID)) | \ + (PTE_TYPE_PAGE & ~PTE_VALID))) #define pte_none(pte) (!pte_val(pte)) #define pte_page(pte) (pfn_to_page(pte_pfn(pte)))
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 1662c5a8f445..a4dbd81d42bf 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h@@ -738,6 +738,10 @@ static inline pgprotval_t check_pgprot(pgprot_t pgprot) static inline pte_t pfn_pte(unsigned long page_nr, pgprot_t pgprot) { phys_addr_t pfn = (phys_addr_t)page_nr << PAGE_SHIFT; + + /* Filter out _PAGE_PSE to ensure PTEs never carry the huge page bit */ + pgprot = __pgprot(pgprot_val(pgprot) & ~_PAGE_PSE); + /* This bit combination is used to mark shadow stacks */ WARN_ON_ONCE((pgprot_val(pgprot) & (_PAGE_DIRTY | _PAGE_RW)) == _PAGE_DIRTY);
--
2.22.0