linux-hardening - [RFC PATCH 05/12] arm64: mm: remap PUD pages r/o in linear region

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Message-Id: <20220126173011.3476262-6-ardb@kernel.org>
Date:   Wed, 26 Jan 2022 18:30:04 +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 05/12] arm64: mm: remap PUD pages r/o in linear region

Implement the arch specific PUD alloc/free helpers by wrapping the
generic code, and remapping the page read-only on allocation and
read-write on free.

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              | 20 ++++++++++++++++++++
 3 files changed, 27 insertions(+)

diff --git a/arch/arm64/include/asm/pgalloc.h b/arch/arm64/include/asm/pgalloc.h
index d54ac9f8d6c7..737e9f32b199 100644
--- a/arch/arm64/include/asm/pgalloc.h
+++ b/arch/arm64/include/asm/pgalloc.h
@@ -14,6 +14,8 @@
 #include <asm/tlbflush.h>
 
 #define __HAVE_ARCH_PGD_FREE
+#define __HAVE_ARCH_PUD_ALLOC_ONE
+#define __HAVE_ARCH_PUD_FREE
 #include <asm-generic/pgalloc.h>
 
 #define PGD_SIZE	(PTRS_PER_PGD * sizeof(pgd_t))
@@ -45,6 +47,9 @@ static inline void __pud_populate(pud_t *pudp, phys_addr_t pmdp, pudval_t prot)
 
 #if CONFIG_PGTABLE_LEVELS > 3
 
+pud_t *pud_alloc_one(struct mm_struct *mm, unsigned long addr);
+void pud_free(struct mm_struct *mm, pud_t *pud);
+
 static inline void __p4d_populate(p4d_t *p4dp, phys_addr_t pudp, p4dval_t prot)
 {
 	set_p4d(p4dp, __p4d(__phys_to_p4d_val(pudp) | prot));
diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h
index c995d1f4594f..6557626752fc 100644
--- a/arch/arm64/include/asm/tlb.h
+++ b/arch/arm64/include/asm/tlb.h
@@ -94,6 +94,8 @@ static inline void __pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmdp,
 static inline void __pud_free_tlb(struct mmu_gather *tlb, pud_t *pudp,
 				  unsigned long addr)
 {
+	if (page_tables_are_ro())
+		set_pgtable_rw(pudp);
 	tlb_remove_table(tlb, virt_to_page(pudp));
 }
 #endif
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index a52c3162beae..03d77c4c3570 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1645,3 +1645,23 @@ static int __init prevent_bootmem_remove_init(void)
 }
 early_initcall(prevent_bootmem_remove_init);
 #endif
+
+#ifndef __PAGETABLE_PUD_FOLDED
+pud_t *pud_alloc_one(struct mm_struct *mm, unsigned long addr)
+{
+	pud_t *pud = __pud_alloc_one(mm, addr);
+
+	if (!pud)
+		return NULL;
+	if (page_tables_are_ro())
+		set_pgtable_ro(pud);
+	return pud;
+}
+
+void pud_free(struct mm_struct *mm, pud_t *pud)
+{
+	if (page_tables_are_ro())
+		set_pgtable_rw(pud);
+	free_page((u64)pud);
+}
+#endif
-- 
2.30.2