[PATCHv4 4/7] arm64: Move some head.text functions to executable section

[Ard Biesheuvel]

On 27 October 2014 21:12, Laura Abbott <lauraa at codeaurora.org> wrote:
> The head.text section is intended to be run at early bootup
> before any of the regular kernel mappings have been setup.
> Parts of head.text may be freed back into the buddy allocator
> due to TEXT_OFFSET so for security requirements this memory
> must not be executable. The suspend/resume/hotplug code path
> requires some of these head.S functions to run however which
> means they need to be executable. Support these conflicting
> requirements by moving the few head.text functions that need
> to be executable to the text section which has the appropriate
> page table permissions.
>
> Signed-off-by: Laura Abbott <lauraa at codeaurora.org>
> ---
> v4: New apprach based on discussions with Mark
> ---
>  arch/arm64/kernel/head.S | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index 10f5cc0..dc362da 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -432,12 +432,14 @@ ENTRY(secondary_startup)
>         b       __enable_mmu
>  ENDPROC(secondary_startup)
>
> +       .pushsection    .text, "ax"
>  ENTRY(__secondary_switched)
>         ldr     x0, [x21]                       // get secondary_data.stack
>         mov     sp, x0
>         mov     x29, #0
>         b       secondary_start_kernel
>  ENDPROC(__secondary_switched)
> +       .popsection
>  #endif /* CONFIG_SMP */
>
>  /*
> @@ -471,11 +473,13 @@ ENDPROC(__enable_mmu)
>   * table to map the entire function.
>   */
>         .align  4
> +       .pushsection    .text, "ax"

There is a comment before this .align that explains why it is
separated from __enable_mmu, and I think jumping into another section
right after it kind of defeats the purpose.
Perhaps it is better to put the pushsection before __enable_mmu instead?

>  __turn_mmu_on:
>         msr     sctlr_el1, x0
>         isb
>         br      x27
>  ENDPROC(__turn_mmu_on)
> +       .popsection
>
>  /*
>   * Calculate the start of physical memory.
> --
> Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
>
>
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