[PATCH v1 12/18] arm64: add PTE_UXN/PTE_WRITE to SWAPPER_*_FLAGS

[Catalin Marinas]

On Thu, Mar 09, 2023 at 02:52:40PM +0000, Joey Gouly wrote:
> With PIE enabled, the swapper PTEs would have a Permission Indirection Index (PIIndex)
> of 0. A PIIndex of 0 is not currently used by any other PTEs.
> 
> To avoid using index 0 specifically for the swapper PTEs, mark them as PTE_UXN
> and PTE_WRITE, so that they map to a PAGE_KERNEL_EXEC equivalent.
> 
> Signed-off-by: Joey Gouly <joey.gouly at arm.com>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Will Deacon <will at kernel.org>
> Cc: Mark Rutland <mark.rutland at arm.com>
> ---
>  arch/arm64/include/asm/kernel-pgtable.h | 4 ++--
>  arch/arm64/kernel/head.S                | 8 ++++----
>  arch/arm64/mm/proc.S                    | 2 +-
>  3 files changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kernel-pgtable.h b/arch/arm64/include/asm/kernel-pgtable.h
> index fcd14197756f..daf1909116f6 100644
> --- a/arch/arm64/include/asm/kernel-pgtable.h
> +++ b/arch/arm64/include/asm/kernel-pgtable.h
> @@ -104,8 +104,8 @@
>  /*
>   * Initial memory map attributes.
>   */
> -#define SWAPPER_PTE_FLAGS	(PTE_TYPE_PAGE | PTE_AF | PTE_SHARED)
> -#define SWAPPER_PMD_FLAGS	(PMD_TYPE_SECT | PMD_SECT_AF | PMD_SECT_S)
> +#define SWAPPER_PTE_FLAGS	(PTE_TYPE_PAGE | PTE_AF | PTE_SHARED | PTE_UXN | PTE_WRITE)
> +#define SWAPPER_PMD_FLAGS	(PMD_TYPE_SECT | PMD_SECT_AF | PMD_SECT_S | PTE_UXN | PTE_WRITE)

Adding PTE_UXN is fine but we have SWAPPER_RX_MMUFLAGS which is no
longer read-only after this change. I don't think this matters much as
IIUC we only use init_pg_dir briefly before creating the proper
swapper_pg_dir.

-- 
Catalin