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Date: Mon, 4 Sep 2017 12:08:25 -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 05/29] ARM: head-common.S: use PC-relative insn sequence
for idmap creation
On Sun, 3 Sep 2017, Ard Biesheuvel wrote:
> Replace the open coded PC relative offset calculations involving
> __turn_mmu_on and __turn_mmu_on_end with a pair of adr_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 | 12 ++----------
> 1 file changed, 2 insertions(+), 10 deletions(-)
>
> diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
> index 04286fd9e09c..0a98aec0e39d 100644
> --- a/arch/arm/kernel/head.S
> +++ b/arch/arm/kernel/head.S
> @@ -227,11 +227,8 @@ __create_page_tables:
> * Create identity mapping to cater for __enable_mmu.
> * This identity mapping will be removed by paging_init().
> */
> - adr r0, __turn_mmu_on_loc
> - ldmia r0, {r3, r5, r6}
> - sub r0, r0, r3 @ virt->phys offset
> - add r5, r5, r0 @ phys __turn_mmu_on
> - add r6, r6, r0 @ phys __turn_mmu_on_end
> + adr_l r5, __turn_mmu_on @ _pa(__turn_mmu_on)
> + adr_l r6, __turn_mmu_on_end @ _pa(__turn_mmu_on_end)
> mov r5, r5, lsr #SECTION_SHIFT
> mov r6, r6, lsr #SECTION_SHIFT
>
> @@ -354,11 +351,6 @@ __create_page_tables:
> ret lr
> ENDPROC(__create_page_tables)
> .ltorg
> - .align
> -__turn_mmu_on_loc:
> - .long .
> - .long __turn_mmu_on
> - .long __turn_mmu_on_end
>
> #if defined(CONFIG_SMP)
> .text
> --
> 2.11.0
>
>
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