[PATCH v2 3/3] arm64: mm: use XN table mapping attributes for user/kernel mappings

[Anshuman Khandual]

On 3/8/21 11:45 PM, Ard Biesheuvel wrote:
> As the kernel and user space page tables are strictly mutually exclusive
> when it comes to executable permissions, we can set the UXN table attribute
> on all table entries that are created while creating kernel mappings in the
> swapper page tables, and the PXN table attribute on all table entries that
> are created while creating user space mappings in user space page tables.
> 
> While at it, get rid of a redundant comment.
> 
> Signed-off-by: Ard Biesheuvel <ardb at kernel.org>

Reviewed-by: Anshuman Khandual <anshuman.khandual at arm.com>

> ---
>  arch/arm64/include/asm/pgalloc.h | 19 ++++++++++++-------
>  1 file changed, 12 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/pgalloc.h b/arch/arm64/include/asm/pgalloc.h
> index 27cc643d0509..31fbab3d6f99 100644
> --- a/arch/arm64/include/asm/pgalloc.h
> +++ b/arch/arm64/include/asm/pgalloc.h
> @@ -27,7 +27,10 @@ static inline void __pud_populate(pud_t *pudp, phys_addr_t pmdp, pudval_t prot)
>  
>  static inline void pud_populate(struct mm_struct *mm, pud_t *pudp, pmd_t *pmdp)
>  {
> -	__pud_populate(pudp, __pa(pmdp), PUD_TYPE_TABLE);
> +	pudval_t pudval = PUD_TYPE_TABLE;
> +
> +	pudval |= (mm == &init_mm) ? PUD_TABLE_UXN : PUD_TABLE_PXN;
> +	__pud_populate(pudp, __pa(pmdp), pudval);
>  }
>  #else
>  static inline void __pud_populate(pud_t *pudp, phys_addr_t pmdp, pudval_t prot)
> @@ -45,7 +48,10 @@ static inline void __p4d_populate(p4d_t *p4dp, phys_addr_t pudp, p4dval_t prot)
>  
>  static inline void p4d_populate(struct mm_struct *mm, p4d_t *p4dp, pud_t *pudp)
>  {
> -	__p4d_populate(p4dp, __pa(pudp), P4D_TYPE_TABLE);
> +	p4dval_t p4dval = P4D_TYPE_TABLE;
> +
> +	p4dval |= (mm == &init_mm) ? P4D_TABLE_UXN : P4D_TABLE_PXN;
> +	__p4d_populate(p4dp, __pa(pudp), p4dval);
>  }
>  #else
>  static inline void __p4d_populate(p4d_t *p4dp, phys_addr_t pudp, p4dval_t prot)
> @@ -70,16 +76,15 @@ static inline void __pmd_populate(pmd_t *pmdp, phys_addr_t ptep,
>  static inline void
>  pmd_populate_kernel(struct mm_struct *mm, pmd_t *pmdp, pte_t *ptep)
>  {
> -	/*
> -	 * The pmd must be loaded with the physical address of the PTE table
> -	 */
> -	__pmd_populate(pmdp, __pa(ptep), PMD_TYPE_TABLE);
> +	VM_BUG_ON(mm != &init_mm);
> +	__pmd_populate(pmdp, __pa(ptep), PMD_TYPE_TABLE | PMD_TABLE_UXN);
>  }
>  
>  static inline void
>  pmd_populate(struct mm_struct *mm, pmd_t *pmdp, pgtable_t ptep)
>  {
> -	__pmd_populate(pmdp, page_to_phys(ptep), PMD_TYPE_TABLE);
> +	VM_BUG_ON(mm == &init_mm);
> +	__pmd_populate(pmdp, page_to_phys(ptep), PMD_TYPE_TABLE | PMD_TABLE_PXN);
>  }
>  #define pmd_pgtable(pmd) pmd_page(pmd)
>  
>