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

[Steve Capper]

On Mon, Dec 04, 2017 at 02:13:38PM +0000, Ard Biesheuvel wrote:
> 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 ^^^
>

Thanks, I will update this.

> > -       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>

Thanks Ard!

Cheers,
--
Steve
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