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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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