Re: [PATCH] arm64: entry: simplify trampoline data page

[Ard Biesheuvel <ardb@kernel.org>]

On Wed, 27 Apr 2022 at 12:23, Ard Biesheuvel <ardb@kernel.org> wrote:
>
> Get rid of some clunky open coded arithmetic on section addresses, by
> emitting the trampoline data variables into a separate, dedicated r/o
> data section, and putting it at the next page boundary. This way, we can
> access the literals via single LDR instruction.
>
> While at it, get rid of other, implicit literals, and use ADRP/ADD or
> MOVZ/MOVK sequences, as appropriate. Note that the latter are only
> supported for CONFIG_RELOCATABLE=n (which is usually the case if
> CONFIG_RANDOMIZE_BASE=n), so update the CPP conditionals to reflect
> this.
>
> Cc: James Morse <james.morse@arm.com>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

Ping, in case this one slipped behind the desk.

> ---
>  arch/arm64/include/asm/fixmap.h |  4 +-
>  arch/arm64/kernel/entry.S       | 45 ++++++--------------
>  arch/arm64/kernel/vmlinux.lds.S |  3 +-
>  arch/arm64/mm/mmu.c             | 10 ++---
>  4 files changed, 22 insertions(+), 40 deletions(-)
>
> diff --git a/arch/arm64/include/asm/fixmap.h b/arch/arm64/include/asm/fixmap.h
> index daff882883f9..71ed5fdf718b 100644
> --- a/arch/arm64/include/asm/fixmap.h
> +++ b/arch/arm64/include/asm/fixmap.h
> @@ -62,10 +62,12 @@ enum fixed_addresses {
>  #endif /* CONFIG_ACPI_APEI_GHES */
>
>  #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
> +#ifdef CONFIG_RELOCATABLE
> +       FIX_ENTRY_TRAMP_TEXT4,  /* one extra slot for the data page */
> +#endif
>         FIX_ENTRY_TRAMP_TEXT3,
>         FIX_ENTRY_TRAMP_TEXT2,
>         FIX_ENTRY_TRAMP_TEXT1,
> -       FIX_ENTRY_TRAMP_DATA,
>  #define TRAMP_VALIAS           (__fix_to_virt(FIX_ENTRY_TRAMP_TEXT1))
>  #endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
>         __end_of_permanent_fixed_addresses,
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index ede028dee81b..aed2b41e05aa 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -636,18 +636,20 @@ alternative_else_nop_endif
>          */
>         .endm
>
> -       .macro tramp_data_page  dst
> -       adr_l   \dst, .entry.tramp.text
> -       sub     \dst, \dst, PAGE_SIZE
> -       .endm
> -
> -       .macro tramp_data_read_var      dst, var
> -#ifdef CONFIG_RANDOMIZE_BASE
> -       tramp_data_page         \dst
> -       add     \dst, \dst, #:lo12:__entry_tramp_data_\var
> -       ldr     \dst, [\dst]
> +       .macro          tramp_data_read_var     dst, var
> +#ifdef CONFIG_RELOCATABLE
> +       ldr             \dst, .L__tramp_data_\var
> +       .ifndef         .L__tramp_data_\var
> +       .pushsection    ".entry.tramp.rodata", "a", %progbits
> +       .align          3
> +.L__tramp_data_\var:
> +       .quad           \var
> +       .popsection
> +       .endif
>  #else
> -       ldr     \dst, =\var
> +       movz            \dst, :abs_g2_s:\var
> +       movk            \dst, :abs_g1_nc:\var
> +       movk            \dst, :abs_g0_nc:\var
>  #endif
>         .endm
>
> @@ -695,7 +697,7 @@ alternative_else_nop_endif
>         msr     vbar_el1, x30
>         isb
>         .else
> -       ldr     x30, =vectors
> +       adr_l   x30, vectors
>         .endif // \kpti == 1
>
>         .if     \bhb == BHB_MITIGATION_FW
> @@ -764,24 +766,7 @@ SYM_CODE_END(tramp_exit_native)
>  SYM_CODE_START(tramp_exit_compat)
>         tramp_exit      32
>  SYM_CODE_END(tramp_exit_compat)
> -
> -       .ltorg
>         .popsection                             // .entry.tramp.text
> -#ifdef CONFIG_RANDOMIZE_BASE
> -       .pushsection ".rodata", "a"
> -       .align PAGE_SHIFT
> -SYM_DATA_START(__entry_tramp_data_start)
> -__entry_tramp_data_vectors:
> -       .quad   vectors
> -#ifdef CONFIG_ARM_SDE_INTERFACE
> -__entry_tramp_data___sdei_asm_handler:
> -       .quad   __sdei_asm_handler
> -#endif /* CONFIG_ARM_SDE_INTERFACE */
> -__entry_tramp_data_this_cpu_vector:
> -       .quad   this_cpu_vector
> -SYM_DATA_END(__entry_tramp_data_start)
> -       .popsection                             // .rodata
> -#endif /* CONFIG_RANDOMIZE_BASE */
>  #endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
>
>  /*
> @@ -932,7 +917,6 @@ NOKPROBE(call_on_irq_stack)
>   * This clobbers x4, __sdei_handler() will restore this from firmware's
>   * copy.
>   */
> -.ltorg
>  .pushsection ".entry.tramp.text", "ax"
>  SYM_CODE_START(__sdei_asm_entry_trampoline)
>         mrs     x4, ttbr1_el1
> @@ -967,7 +951,6 @@ SYM_CODE_START(__sdei_asm_exit_trampoline)
>  1:     sdei_handler_exit exit_mode=x2
>  SYM_CODE_END(__sdei_asm_exit_trampoline)
>  NOKPROBE(__sdei_asm_exit_trampoline)
> -       .ltorg
>  .popsection            // .entry.tramp.text
>  #endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */
>
> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> index edaf0faf766f..17e554be9198 100644
> --- a/arch/arm64/kernel/vmlinux.lds.S
> +++ b/arch/arm64/kernel/vmlinux.lds.S
> @@ -117,7 +117,8 @@ jiffies = jiffies_64;
>         __entry_tramp_text_start = .;                   \
>         *(.entry.tramp.text)                            \
>         . = ALIGN(PAGE_SIZE);                           \
> -       __entry_tramp_text_end = .;
> +       __entry_tramp_text_end = .;                     \
> +       *(.entry.tramp.rodata)
>  #else
>  #define TRAMP_TEXT
>  #endif
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 626ec32873c6..be4d6c3f5692 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -665,13 +665,9 @@ static int __init map_entry_trampoline(void)
>                 __set_fixmap(FIX_ENTRY_TRAMP_TEXT1 - i,
>                              pa_start + i * PAGE_SIZE, prot);
>
> -       if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
> -               extern char __entry_tramp_data_start[];
> -
> -               __set_fixmap(FIX_ENTRY_TRAMP_DATA,
> -                            __pa_symbol(__entry_tramp_data_start),
> -                            PAGE_KERNEL_RO);
> -       }
> +       if (IS_ENABLED(CONFIG_RELOCATABLE))
> +               __set_fixmap(FIX_ENTRY_TRAMP_TEXT1 - i,
> +                            pa_start + i * PAGE_SIZE, PAGE_KERNEL_RO);
>
>         return 0;
>  }
> --
> 2.30.2
>

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel