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Date: Mon, 4 Sep 2017 14:30:13 -0400 (EDT)
From: Nicolas Pitre <nicolas.pitre@...aro.org>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>
cc: linux-arm-kernel@...ts.infradead.org, kernel-hardening@...ts.openwall.com, 
    Arnd Bergmann <arnd@...db.de>, Russell King <linux@...linux.org.uk>, 
    Kees Cook <keescook@...omium.org>, Thomas Garnier <thgarnie@...gle.com>, 
    Marc Zyngier <marc.zyngier@....com>, Mark Rutland <mark.rutland@....com>, 
    Tony Lindgren <tony@...mide.com>, Matt Fleming <matt@...eblueprint.co.uk>, 
    Dave Martin <dave.martin@....com>
Subject: Re: [PATCH v2 23/29] ARM: kernel: refer to swapper_pg_dir via its
 symbol

On Sun, 3 Sep 2017, Ard Biesheuvel wrote:

> The location of swapper_pg_dir is relative to the kernel, not to
> PAGE_OFFSET or PHYS_OFFSET. So define the symbol relative to the
> start of the kernel image, and refer to it via its name.

Could it cause a section access mismatch if defined in the __HEAD 
section?

Otherwise

Acked-by: Nicolas Pitre <nico@...aro.org>

> 
> Cc: Russell King <linux@...linux.org.uk>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> ---
>  arch/arm/kernel/head.S | 13 ++++---------
>  1 file changed, 4 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
> index 5d685e86148c..71bc0d037bc9 100644
> --- a/arch/arm/kernel/head.S
> +++ b/arch/arm/kernel/head.S
> @@ -48,14 +48,6 @@
>  #define PMD_ORDER	2
>  #endif
>  
> -	.globl	swapper_pg_dir
> -	.equ	swapper_pg_dir, KERNEL_RAM_VADDR - PG_DIR_SIZE
> -
> -	.macro	pgtbl, rd, phys
> -	add	\rd, \phys, #TEXT_OFFSET
> -	sub	\rd, \rd, #PG_DIR_SIZE
> -	.endm
> -
>  /*
>   * Kernel startup entry point.
>   * ---------------------------
> @@ -77,6 +69,9 @@
>  	.arm
>  
>  	__HEAD
> +	.globl	swapper_pg_dir
> +	.equ	swapper_pg_dir, . - PG_DIR_SIZE
> +
>  ENTRY(stext)
>   ARM_BE8(setend	be )			@ ensure we are in BE8 mode
>  
> @@ -172,7 +167,7 @@ ENDPROC(stext)
>   *  r4 = physical page table address
>   */
>  __create_page_tables:
> -	pgtbl	r4, r8				@ page table address
> +	adr_l	r4, swapper_pg_dir		@ page table address
>  
>  	/*
>  	 * Clear the swapper page table
> -- 
> 2.11.0
> 
> 

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