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Message-ID: <nycvar.YSQ.7.76.1709041215010.8603@knanqh.ubzr>
Date: Mon, 4 Sep 2017 12:15:32 -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 07/29] ARM: kernel: use relative references for UP/SMP
alternatives
On Sun, 3 Sep 2017, Ard Biesheuvel wrote:
> To avoid absolute references that are subject to runtime relocation
> when running a kernel built with CONFIG_RELOCATABLE=y, use relative
> references in the smp.alt entries.
>
> 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/include/asm/assembler.h | 4 ++--
> arch/arm/include/asm/processor.h | 2 +-
> arch/arm/kernel/head.S | 10 +++++-----
> 3 files changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
> index 341e4ed1ef84..a0906c1fc65d 100644
> --- a/arch/arm/include/asm/assembler.h
> +++ b/arch/arm/include/asm/assembler.h
> @@ -260,7 +260,7 @@
> */
> #define ALT_UP(instr...) \
> .pushsection ".alt.smp.init", "a" ;\
> - .long 9998b ;\
> + .long 9998b - . ;\
> 9997: instr ;\
> .if . - 9997b == 2 ;\
> nop ;\
> @@ -272,7 +272,7 @@
> #define ALT_UP_B(label) \
> .equ up_b_offset, label - 9998b ;\
> .pushsection ".alt.smp.init", "a" ;\
> - .long 9998b ;\
> + .long 9998b - . ;\
> W(b) . + up_b_offset ;\
> .popsection
> #else
> diff --git a/arch/arm/include/asm/processor.h b/arch/arm/include/asm/processor.h
> index c3d5fc124a05..3667b395bb17 100644
> --- a/arch/arm/include/asm/processor.h
> +++ b/arch/arm/include/asm/processor.h
> @@ -92,7 +92,7 @@ unsigned long get_wchan(struct task_struct *p);
> #define __ALT_SMP_ASM(smp, up) \
> "9998: " smp "\n" \
> " .pushsection \".alt.smp.init\", \"a\"\n" \
> - " .long 9998b\n" \
> + " .long 9998b - .\n" \
> " " up "\n" \
> " .popsection\n"
> #else
> diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
> index 6e9df3663a57..ec22f42fd8bb 100644
> --- a/arch/arm/kernel/head.S
> +++ b/arch/arm/kernel/head.S
> @@ -548,14 +548,15 @@ smp_on_up:
> __do_fixup_smp_on_up:
> cmp r4, r5
> reths lr
> - ldmia r4!, {r0, r6}
> - ARM( str r6, [r0, r3] )
> - THUMB( add r0, r0, r3 )
> + ldmia r4, {r0, r6}
> + ARM( str r6, [r0, r4] )
> + THUMB( add r0, r0, r4 )
> + add r4, r4, #8
> #ifdef __ARMEB__
> THUMB( mov r6, r6, ror #16 ) @ Convert word order for big-endian.
> #endif
> THUMB( strh r6, [r0], #2 ) @ For Thumb-2, store as two halfwords
> - THUMB( mov r6, r6, lsr #16 ) @ to be robust against misaligned r3.
> + THUMB( mov r6, r6, lsr #16 ) @ to be robust against misaligned r0.
> THUMB( strh r6, [r0] )
> b __do_fixup_smp_on_up
> ENDPROC(__do_fixup_smp_on_up)
> @@ -564,7 +565,6 @@ ENTRY(fixup_smp)
> stmfd sp!, {r4 - r6, lr}
> mov r4, r0
> add r5, r0, r1
> - mov r3, #0
> bl __do_fixup_smp_on_up
> ldmfd sp!, {r4 - r6, pc}
> ENDPROC(fixup_smp)
> --
> 2.11.0
>
>
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