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Message-ID: <nycvar.YSQ.7.76.1709041246410.8603@knanqh.ubzr>
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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