linux-hardening - [RFC PATCH 06/12] arm64: mm: remap PMD pages r/o in linear region

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Date:   Wed, 26 Jan 2022 18:30:05 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     kvmarm@...ts.cs.columbia.edu, linux-hardening@...r.kernel.org,
        Ard Biesheuvel <ardb@...nel.org>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Fuad Tabba <tabba@...gle.com>,
        Quentin Perret <qperret@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        Catalin Marinas <catalin.marinas@....com>
Subject: [RFC PATCH 06/12] arm64: mm: remap PMD pages r/o in linear region

PMD modifications all go through the fixmap update routine, so there is
no longer a need to keep it mapped read/write in the linear region.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/arm64/include/asm/pgalloc.h |  5 +++++
 arch/arm64/include/asm/tlb.h     |  2 ++
 arch/arm64/mm/mmu.c              | 21 ++++++++++++++++++++
 3 files changed, 28 insertions(+)

diff --git a/arch/arm64/include/asm/pgalloc.h b/arch/arm64/include/asm/pgalloc.h
index 737e9f32b199..63f9ae9e96fe 100644
--- a/arch/arm64/include/asm/pgalloc.h
+++ b/arch/arm64/include/asm/pgalloc.h
@@ -16,12 +16,17 @@
 #define __HAVE_ARCH_PGD_FREE
 #define __HAVE_ARCH_PUD_ALLOC_ONE
 #define __HAVE_ARCH_PUD_FREE
+#define __HAVE_ARCH_PMD_ALLOC_ONE
+#define __HAVE_ARCH_PMD_FREE
 #include <asm-generic/pgalloc.h>
 
 #define PGD_SIZE	(PTRS_PER_PGD * sizeof(pgd_t))
 
 #if CONFIG_PGTABLE_LEVELS > 2
 
+pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long addr);
+void pmd_free(struct mm_struct *mm, pmd_t *pmd);
+
 static inline void __pud_populate(pud_t *pudp, phys_addr_t pmdp, pudval_t prot)
 {
 	set_pud(pudp, __pud(__phys_to_pud_val(pmdp) | prot));
diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h
index 6557626752fc..0f54fbb59bba 100644
--- a/arch/arm64/include/asm/tlb.h
+++ b/arch/arm64/include/asm/tlb.h
@@ -85,6 +85,8 @@ static inline void __pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmdp,
 {
 	struct page *page = virt_to_page(pmdp);
 
+	if (page_tables_are_ro())
+		set_pgtable_rw(pmdp);
 	pgtable_pmd_page_dtor(page);
 	tlb_remove_table(tlb, page);
 }
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 03d77c4c3570..e55d91a5f1ed 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1665,3 +1665,24 @@ void pud_free(struct mm_struct *mm, pud_t *pud)
 	free_page((u64)pud);
 }
 #endif
+
+#ifndef __PAGETABLE_PMD_FOLDED
+pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long addr)
+{
+	pmd_t *pmd = __pmd_alloc_one(mm, addr);
+
+	if (!pmd)
+		return NULL;
+	if (page_tables_are_ro())
+		set_pgtable_ro(pmd);
+	return pmd;
+}
+
+void pmd_free(struct mm_struct *mm, pmd_t *pmd)
+{
+	if (page_tables_are_ro())
+		set_pgtable_rw(pmd);
+	pgtable_pmd_page_dtor(virt_to_page(pmd));
+	free_page((u64)pmd);
+}
+#endif
-- 
2.30.2