Commit 004fc58f authored by Anshuman Khandual's avatar Anshuman Khandual Committed by Catalin Marinas
Browse files

arm64/mm: Intercept pfn changes in set_pte_at() 



Changing pfn on a user page table mapped entry, without first going through
break-before-make (BBM) procedure is unsafe. This just updates set_pte_at()
to intercept such changes, via an updated pgattr_change_is_safe(). This new
check happens via __check_racy_pte_update(), which has now been renamed as
__check_safe_pte_update().

Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Acked-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarAnshuman Khandual <anshuman.khandual@arm.com>
Link: https://lore.kernel.org/r/20230130121457.1607675-1-anshuman.khandual@arm.com


Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent a70f00e7

arch/arm64/include/asm/pgtable.h

+6 −2
Original line number Diff line number Diff line
@@ -275,6 +275,7 @@ static inline void set_pte(pte_t *ptep, pte_t pte) 
}



extern void __sync_icache_dcache(pte_t pteval);

bool pgattr_change_is_safe(u64 old, u64 new);



/*

 * PTE bits configuration in the presence of hardware Dirty Bit Management
@@ -292,7 +293,7 @@ extern void __sync_icache_dcache(pte_t pteval); 
 *   PTE_DIRTY || (PTE_WRITE && !PTE_RDONLY)

 */



static inline void __check_racy_pte_update(struct mm_struct *mm, pte_t *ptep,

static inline void __check_safe_pte_update(struct mm_struct *mm, pte_t *ptep,

					   pte_t pte)

{

	pte_t old_pte;
@@ -318,6 +319,9 @@ static inline void __check_racy_pte_update(struct mm_struct *mm, pte_t *ptep, 
	VM_WARN_ONCE(pte_write(old_pte) && !pte_dirty(pte),

		     "%s: racy dirty state clearing: 0x%016llx -> 0x%016llx",

		     __func__, pte_val(old_pte), pte_val(pte));

	VM_WARN_ONCE(!pgattr_change_is_safe(pte_val(old_pte), pte_val(pte)),

		     "%s: unsafe attribute change: 0x%016llx -> 0x%016llx",

		     __func__, pte_val(old_pte), pte_val(pte));

}



static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr,
@@ -346,7 +350,7 @@ static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr, 
			mte_sync_tags(old_pte, pte);

	}



	__check_racy_pte_update(mm, ptep, pte);

	__check_safe_pte_update(mm, ptep, pte);



	set_pte(ptep, pte);

}

arch/arm64/mm/mmu.c

+6 −2
Original line number Diff line number Diff line
@@ -133,7 +133,7 @@ static phys_addr_t __init early_pgtable_alloc(int shift) 
	return phys;

}



static bool pgattr_change_is_safe(u64 old, u64 new)

bool pgattr_change_is_safe(u64 old, u64 new)

{

	/*

	 * The following mapping attributes may be updated in live
@@ -142,9 +142,13 @@ static bool pgattr_change_is_safe(u64 old, u64 new) 
	pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG;



	/* creating or taking down mappings is always safe */

	if (old == 0 || new == 0)

	if (!pte_valid(__pte(old)) || !pte_valid(__pte(new)))

		return true;



	/* A live entry's pfn should not change */

	if (pte_pfn(__pte(old)) != pte_pfn(__pte(new)))

		return false;



	/* live contiguous mappings may not be manipulated at all */

	if ((old | new) & PTE_CONT)

		return false;