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Date: Mon, 4 Sep 2017 12:06:50 -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 04/29] ARM: head-common.S: use PC-relative insn sequence
for __proc_info
On Sun, 3 Sep 2017, Ard Biesheuvel wrote:
> Replace the open coded PC relative offset calculations 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-common.S | 22 ++++++--------------
> 1 file changed, 6 insertions(+), 16 deletions(-)
>
> diff --git a/arch/arm/kernel/head-common.S b/arch/arm/kernel/head-common.S
> index 8733012d231f..06035488130c 100644
> --- a/arch/arm/kernel/head-common.S
> +++ b/arch/arm/kernel/head-common.S
> @@ -150,11 +150,12 @@ ENDPROC(lookup_processor_type)
> * r9 = cpuid (preserved)
> */
> __lookup_processor_type:
> - adr r3, __lookup_processor_type_data
> - ldmia r3, {r4 - r6}
> - sub r3, r3, r4 @ get offset between virt&phys
> - add r5, r5, r3 @ convert virt addresses to
> - add r6, r6, r3 @ physical address space
> + /*
> + * Look in <asm/procinfo.h> for information about the __proc_info
> + * structure.
> + */
> + adr_l r5, __proc_info_begin
> + adr_l r6, __proc_info_end
> 1: ldmia r5, {r3, r4} @ value, mask
> and r4, r4, r9 @ mask wanted bits
> teq r3, r4
> @@ -166,17 +167,6 @@ __lookup_processor_type:
> 2: ret lr
> ENDPROC(__lookup_processor_type)
>
> -/*
> - * Look in <asm/procinfo.h> for information about the __proc_info structure.
> - */
> - .align 2
> - .type __lookup_processor_type_data, %object
> -__lookup_processor_type_data:
> - .long .
> - .long __proc_info_begin
> - .long __proc_info_end
> - .size __lookup_processor_type_data, . - __lookup_processor_type_data
> -
> __error_lpae:
> #ifdef CONFIG_DEBUG_LL
> adr r0, str_lpae
> --
> 2.11.0
>
>
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