[PATCH V2 1/2] arm64: Re-order reserved_ttbr0 in linker script

[Ard Biesheuvel]

On 23 November 2017 at 16:40, Steve Capper <steve.capper at arm.com> wrote:
> Currently one resolves the location of the reserved_ttbr0 for PAN by
> taking a positive offset from swapper_pg_dir. In a future patch we wish
> to extend the swapper s.t. its size is determined at link time rather
> than compile time, rendering SWAPPER_DIR_SIZE unsuitable for such a low
> level calculation.
>
> In this patch we re-arrange the order of the linker script s.t. instead
> one computes reserved_ttbr0 by subtracting RESERVED_TTBR0_SIZE from
> swapper_pg_dir.
>
> Signed-off-by: Steve Capper <steve.capper at arm.com>
> Acked-by: Mark Rutland <mark.rutland at arm.com>
> ---
>  arch/arm64/include/asm/asm-uaccess.h | 6 +++---
>  arch/arm64/include/asm/uaccess.h     | 2 +-
>  arch/arm64/kernel/vmlinux.lds.S      | 5 ++---
>  3 files changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/include/asm/asm-uaccess.h b/arch/arm64/include/asm/asm-uaccess.h
> index b3da6c886835..e09f02cd3e7a 100644
> --- a/arch/arm64/include/asm/asm-uaccess.h
> +++ b/arch/arm64/include/asm/asm-uaccess.h
> @@ -12,9 +12,9 @@
>   */
>  #ifdef CONFIG_ARM64_SW_TTBR0_PAN
>         .macro  __uaccess_ttbr0_disable, tmp1
> -       mrs     \tmp1, ttbr1_el1                // swapper_pg_dir
> -       add     \tmp1, \tmp1, #SWAPPER_DIR_SIZE // reserved_ttbr0 at the end of swapper_pg_dir
> -       msr     ttbr0_el1, \tmp1                // set reserved TTBR0_EL1
> +       mrs     \tmp1, ttbr1_el1                        // swapper_pg_dir
> +       sub     \tmp1, \tmp1, #RESERVED_TTBR0_SIZE      // reserved_ttbr0 just before swapper_pg_dir
> +       msr     ttbr0_el1, \tmp1                        // set reserved TTBR0_EL1
>         isb
>         .endm
>
> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> index fc0f9eb66039..66170fd4b58f 100644
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -108,7 +108,7 @@ static inline void __uaccess_ttbr0_disable(void)
>         unsigned long ttbr;
>
>         /* reserved_ttbr0 placed at the end of swapper_pg_dir */

You missed a comment here ^^^

> -       ttbr = read_sysreg(ttbr1_el1) + SWAPPER_DIR_SIZE;
> +       ttbr = read_sysreg(ttbr1_el1) - RESERVED_TTBR0_SIZE;
>         write_sysreg(ttbr, ttbr0_el1);
>         isb();
>  }
> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> index 7da3e5c366a0..2a9475733e84 100644
> --- a/arch/arm64/kernel/vmlinux.lds.S
> +++ b/arch/arm64/kernel/vmlinux.lds.S
> @@ -206,13 +206,12 @@ SECTIONS
>         . = ALIGN(PAGE_SIZE);
>         idmap_pg_dir = .;
>         . += IDMAP_DIR_SIZE;
> -       swapper_pg_dir = .;
> -       . += SWAPPER_DIR_SIZE;
> -
>  #ifdef CONFIG_ARM64_SW_TTBR0_PAN
>         reserved_ttbr0 = .;
>         . += RESERVED_TTBR0_SIZE;
>  #endif
> +       swapper_pg_dir = .;
> +       . += SWAPPER_DIR_SIZE;
>
>         __pecoff_data_size = ABSOLUTE(. - __initdata_begin);
>         _end = .;

With that fixed,

Reviewed-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>