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Date: Mon, 4 Sep 2017 12:57:23 -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 12/29] ARM: kvm: replace open coded VA->PA calculations
 with adr_l call

On Sun, 3 Sep 2017, Ard Biesheuvel wrote:

> Replace the open coded calculations of the actual physical address
> of the KVM stub vector table with a single adr_l invocation.
> 
> Cc: Marc Zyngier <marc.zyngier@....com>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>

Acked-by: Nicolas Pitre <nico@...aro.org>

> ---
>  arch/arm/boot/compressed/head.S | 15 ++-------
>  arch/arm/kernel/hyp-stub.S      | 33 +++++++-------------
>  arch/arm/kvm/init.S             |  8 +----
>  3 files changed, 15 insertions(+), 41 deletions(-)
> 
> diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
> index 8a756870c238..5884e8151376 100644
> --- a/arch/arm/boot/compressed/head.S
> +++ b/arch/arm/boot/compressed/head.S
> @@ -427,15 +427,10 @@ dtb_check_done:
>  
>  		/*
>  		 * Compute the address of the hyp vectors after relocation.
> -		 * This requires some arithmetic since we cannot directly
> -		 * reference __hyp_stub_vectors in a PC-relative way.
>  		 * Call __hyp_set_vectors with the new address so that we
>  		 * can HVC again after the copy.
>  		 */
> -0:		adr	r0, 0b
> -		movw	r1, #:lower16:__hyp_stub_vectors - 0b
> -		movt	r1, #:upper16:__hyp_stub_vectors - 0b
> -		add	r0, r0, r1
> +		adr_l	r0, __hyp_stub_vectors
>  		sub	r0, r0, r5
>  		add	r0, r0, r10
>  		bl	__hyp_set_vectors
> @@ -568,17 +563,11 @@ not_relocated:	mov	r0, #0
>  		cmp	r0, #HYP_MODE		@ if not booted in HYP mode...
>  		bne	__enter_kernel		@ boot kernel directly
>  
> -		adr	r12, .L__hyp_reentry_vectors_offset
> -		ldr	r0, [r12]
> -		add	r0, r0, r12
> -
> +		adr_l	r0, __hyp_reentry_vectors
>  		bl	__hyp_set_vectors
>  		__HVC(0)			@ otherwise bounce to hyp mode
>  
>  		b	.			@ should never be reached
> -
> -		.align	2
> -.L__hyp_reentry_vectors_offset:	.long	__hyp_reentry_vectors - .
>  #else
>  		b	__enter_kernel
>  #endif
> diff --git a/arch/arm/kernel/hyp-stub.S b/arch/arm/kernel/hyp-stub.S
> index ec7e7377d423..3c2d1738d3f4 100644
> --- a/arch/arm/kernel/hyp-stub.S
> +++ b/arch/arm/kernel/hyp-stub.S
> @@ -36,41 +36,38 @@ ENTRY(__boot_cpu_mode)
>  .text
>  
>  	/*
> -	 * Save the primary CPU boot mode. Requires 3 scratch registers.
> +	 * Save the primary CPU boot mode. Requires 2 scratch registers.
>  	 */
> -	.macro	store_primary_cpu_mode	reg1, reg2, reg3
> +	.macro	store_primary_cpu_mode	reg1, reg2
>  	mrs	\reg1, cpsr
>  	and	\reg1, \reg1, #MODE_MASK
> -	adr	\reg2, .L__boot_cpu_mode_offset
> -	ldr	\reg3, [\reg2]
> -	str	\reg1, [\reg2, \reg3]
> +	str_l	\reg1, __boot_cpu_mode, \reg2
>  	.endm
>  
>  	/*
>  	 * Compare the current mode with the one saved on the primary CPU.
>  	 * If they don't match, record that fact. The Z bit indicates
>  	 * if there's a match or not.
> -	 * Requires 3 additionnal scratch registers.
> +	 * Requires 2 additional scratch registers.
>  	 */
> -	.macro	compare_cpu_mode_with_primary mode, reg1, reg2, reg3
> -	adr	\reg2, .L__boot_cpu_mode_offset
> -	ldr	\reg3, [\reg2]
> -	ldr	\reg1, [\reg2, \reg3]
> +	.macro	compare_cpu_mode_with_primary mode, reg1, reg2
> +	adr_l	\reg2, __boot_cpu_mode
> +	ldr	\reg1, [\reg2]
>  	cmp	\mode, \reg1		@ matches primary CPU boot mode?
>  	orrne	\reg1, \reg1, #BOOT_CPU_MODE_MISMATCH
> -	strne	\reg1, [\reg2, \reg3]	@ record what happened and give up
> +	strne	\reg1, [\reg2]		@ record what happened and give up
>  	.endm
>  
>  #else	/* ZIMAGE */
>  
> -	.macro	store_primary_cpu_mode	reg1:req, reg2:req, reg3:req
> +	.macro	store_primary_cpu_mode	reg1:req, reg2:req
>  	.endm
>  
>  /*
>   * The zImage loader only runs on one CPU, so we don't bother with mult-CPU
>   * consistency checking:
>   */
> -	.macro	compare_cpu_mode_with_primary mode, reg1, reg2, reg3
> +	.macro	compare_cpu_mode_with_primary mode, reg1, reg2
>  	cmp	\mode, \mode
>  	.endm
>  
> @@ -85,7 +82,7 @@ ENTRY(__boot_cpu_mode)
>   */
>  @ Call this from the primary CPU
>  ENTRY(__hyp_stub_install)
> -	store_primary_cpu_mode	r4, r5, r6
> +	store_primary_cpu_mode	r4, r5
>  ENDPROC(__hyp_stub_install)
>  
>  	@ fall through...
> @@ -99,7 +96,7 @@ ENTRY(__hyp_stub_install_secondary)
>  	 * If the secondary has booted with a different mode, give up
>  	 * immediately.
>  	 */
> -	compare_cpu_mode_with_primary	r4, r5, r6, r7
> +	compare_cpu_mode_with_primary	r4, r5, r6
>  	retne	lr
>  
>  	/*
> @@ -264,12 +261,6 @@ ENTRY(__hyp_reset_vectors)
>  	ret	lr
>  ENDPROC(__hyp_reset_vectors)
>  
> -#ifndef ZIMAGE
> -.align 2
> -.L__boot_cpu_mode_offset:
> -	.long	__boot_cpu_mode - .
> -#endif
> -
>  .align 5
>  ENTRY(__hyp_stub_vectors)
>  __hyp_stub_reset:	W(b)	.
> diff --git a/arch/arm/kvm/init.S b/arch/arm/kvm/init.S
> index 5386528665b5..d777c6fbd869 100644
> --- a/arch/arm/kvm/init.S
> +++ b/arch/arm/kvm/init.S
> @@ -143,13 +143,7 @@ reset:
>  	bic	r1, r1, r0
>  	mcr	p15, 4, r1, c1, c0, 0	@ HSCTLR
>  
> -	/*
> -	 * Install stub vectors, using ardb's VA->PA trick.
> -	 */
> -0:	adr	r0, 0b					@ PA(0)
> -	movw	r1, #:lower16:__hyp_stub_vectors - 0b   @ VA(stub) - VA(0)
> -	movt	r1, #:upper16:__hyp_stub_vectors - 0b
> -	add	r1, r1, r0				@ PA(stub)
> +	adr_l	r1, __hyp_stub_vectors			@ PA(stub)
>  	mcr	p15, 4, r1, c12, c0, 0	@ HVBAR
>  	b	exit
>  
> -- 
> 2.11.0
> 
> 

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