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Date: Mon, 4 Sep 2017 12:47:16 -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 10/29] ARM: head.S: use PC-relative insn sequences
 for __fixup_pv_table

On Sun, 3 Sep 2017, Ard Biesheuvel wrote:

> Replace the open coded PC relative offset calculations with adr_l
> and mov_l invocations. This ensures these quantities are invariant
> under runtime relocation.
> 
> Cc: Russell King <linux@...linux.org.uk>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>

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


> ---
>  arch/arm/kernel/head.S | 27 ++++++--------------
>  1 file changed, 8 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
> index db6b823f20a4..f607e290ef4b 100644
> --- a/arch/arm/kernel/head.S
> +++ b/arch/arm/kernel/head.S
> @@ -578,14 +578,11 @@ ENDPROC(fixup_smp)
>   */
>  	__HEAD
>  __fixup_pv_table:
> -	adr	r0, 1f
> -	ldmia	r0, {r3-r7}
> +	adr_l	r6, __pv_phys_pfn_offset
> +	adr_l	r7, __pv_offset			@ __pa(__pv_offset)
> +	mov_l	r3, __pv_offset			@ __va(__pv_offset)
>  	mvn	ip, #0
> -	subs	r3, r0, r3	@ PHYS_OFFSET - PAGE_OFFSET
> -	add	r4, r4, r3	@ adjust table start address
> -	add	r5, r5, r3	@ adjust table end address
> -	add	r6, r6, r3	@ adjust __pv_phys_pfn_offset address
> -	add	r7, r7, r3	@ adjust __pv_offset address
> +	subs	r3, r7, r3	@ PHYS_OFFSET - PAGE_OFFSET
>  	mov	r0, r8, lsr #PAGE_SHIFT	@ convert to PFN
>  	str	r0, [r6]	@ save computed PHYS_OFFSET to __pv_phys_pfn_offset
>  	strcc	ip, [r7, #HIGH_OFFSET]	@ save to __pv_offset high bits
> @@ -594,20 +591,15 @@ __fixup_pv_table:
>  THUMB(	it	ne		@ cross section branch )
>  	bne	__error
>  	str	r3, [r7, #LOW_OFFSET]	@ save to __pv_offset low bits
> +	adr_l	r4, __pv_table_begin
> +	adr_l	r5, __pv_table_end
>  	b	__fixup_a_pv_table
>  ENDPROC(__fixup_pv_table)
> -
> -	.align
> -1:	.long	.
> -	.long	__pv_table_begin
> -	.long	__pv_table_end
> -2:	.long	__pv_phys_pfn_offset
> -	.long	__pv_offset
> +	.ltorg
>  
>  	.text
>  __fixup_a_pv_table:
> -	adr	r0, 3f
> -	ldr	r6, [r0]
> +	mov_l	r6, __pv_offset
>  	add	r6, r6, r3
>  	ldr	r0, [r6, #HIGH_OFFSET]	@ pv_offset high word
>  	ldr	r6, [r6, #LOW_OFFSET]	@ pv_offset low word
> @@ -676,9 +668,6 @@ ARM_BE8(rev16	ip, ip)
>  #endif
>  ENDPROC(__fixup_a_pv_table)
>  
> -	.align
> -3:	.long __pv_offset
> -
>  ENTRY(fixup_pv_table)
>  	stmfd	sp!, {r4 - r7, lr}
>  	mov	r3, #0			@ no offset
> -- 
> 2.11.0
> 
> 

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