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Date: Mon, 4 Sep 2017 12:09:55 -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 06/29] ARM: head.S: use PC-relative insn sequence for
secondary_data
On Sun, 3 Sep 2017, Ard Biesheuvel wrote:
> Replace the open coded PC relative offset calculations with adr_l
> and ldr_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 | 19 ++++---------------
> 1 file changed, 4 insertions(+), 15 deletions(-)
>
> diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
> index 0a98aec0e39d..6e9df3663a57 100644
> --- a/arch/arm/kernel/head.S
> +++ b/arch/arm/kernel/head.S
> @@ -386,10 +386,8 @@ ENTRY(secondary_startup)
> /*
> * Use the page tables supplied from __cpu_up.
> */
> - adr r4, __secondary_data
> - ldmia r4, {r5, r7, r12} @ address to jump to after
> - sub lr, r4, r5 @ mmu has been enabled
> - add r3, r7, lr
> + adr_l r3, secondary_data
> + mov_l r12, __secondary_switched
> ldrd r4, [r3, #0] @ get secondary_data.pgdir
> ARM_BE8(eor r4, r4, r5) @ Swap r5 and r4 in BE:
> ARM_BE8(eor r5, r4, r5) @ it can be done in 3 steps
> @@ -404,22 +402,13 @@ ARM_BE8(eor r4, r4, r5) @ without using a temp reg.
> ENDPROC(secondary_startup)
> ENDPROC(secondary_startup_arm)
>
> - /*
> - * r6 = &secondary_data
> - */
> ENTRY(__secondary_switched)
> - ldr sp, [r7, #12] @ get secondary_data.stack
> + ldr_l r7, secondary_data + 12 @ get secondary_data.stack
> + mov sp, r7
> mov fp, #0
> b secondary_start_kernel
> ENDPROC(__secondary_switched)
>
> - .align
> -
> - .type __secondary_data, %object
> -__secondary_data:
> - .long .
> - .long secondary_data
> - .long __secondary_switched
> #endif /* defined(CONFIG_SMP) */
>
>
> --
> 2.11.0
>
>
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