linux-kernel - Re: [PATCH v3 02/15] arm64: kvm: Move __smccc_workaround_1

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Message-ID: <02322fdac903aa1786c334d0ddd7f38a@kernel.org>
Date:   Thu, 18 Jun 2020 14:57:45 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     David Brazdil <dbrazdil@...gle.com>
Cc:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, android-kvm@...gle.com,
        kernel-team@...roid.com
Subject: Re: [PATCH v3 02/15] arm64: kvm: Move __smccc_workaround_1_smc to
 .rodata

Hi David,

On 2020-06-18 13:25, David Brazdil wrote:
> This snippet of assembly is used by cpu_errata.c to overwrite parts of 
> KVM hyp
> vector. Move it to its own source file and change its ELF section to 
> .rodata.
> 
> Signed-off-by: David Brazdil <dbrazdil@...gle.com>
> ---
>  arch/arm64/kvm/hyp/Makefile    |  1 +
>  arch/arm64/kvm/hyp/hyp-entry.S | 16 ----------------
>  arch/arm64/kvm/hyp/smccc_wa.S  | 30 ++++++++++++++++++++++++++++++
>  3 files changed, 31 insertions(+), 16 deletions(-)
>  create mode 100644 arch/arm64/kvm/hyp/smccc_wa.S
> 
> diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
> index 8c9880783839..5d8357ddc234 100644
> --- a/arch/arm64/kvm/hyp/Makefile
> +++ b/arch/arm64/kvm/hyp/Makefile
> @@ -7,6 +7,7 @@ ccflags-y += -fno-stack-protector 
> -DDISABLE_BRANCH_PROFILING \
>  		$(DISABLE_STACKLEAK_PLUGIN)
> 
>  obj-$(CONFIG_KVM) += hyp.o
> +obj-$(CONFIG_KVM_INDIRECT_VECTORS) += smccc_wa.o
> 
>  hyp-y := vgic-v3-sr.o timer-sr.o aarch32.o vgic-v2-cpuif-proxy.o 
> sysreg-sr.o \
>  	 debug-sr.o entry.o switch.o fpsimd.o tlb.o hyp-entry.o
> diff --git a/arch/arm64/kvm/hyp/hyp-entry.S 
> b/arch/arm64/kvm/hyp/hyp-entry.S
> index 9c5cfb04170e..d362fad97cc8 100644
> --- a/arch/arm64/kvm/hyp/hyp-entry.S
> +++ b/arch/arm64/kvm/hyp/hyp-entry.S
> @@ -318,20 +318,4 @@ SYM_CODE_START(__bp_harden_hyp_vecs)
>  1:	.org __bp_harden_hyp_vecs + __BP_HARDEN_HYP_VECS_SZ
>  	.org 1b
>  SYM_CODE_END(__bp_harden_hyp_vecs)
> -
> -	.popsection

I'd be tempted to leave the .popsection in place, if only for symmetry  
with the initial .pushsection.

> -
> -SYM_CODE_START(__smccc_workaround_1_smc)
> -	esb
> -	sub	sp, sp, #(8 * 4)
> -	stp	x2, x3, [sp, #(8 * 0)]
> -	stp	x0, x1, [sp, #(8 * 2)]
> -	mov	w0, #ARM_SMCCC_ARCH_WORKAROUND_1
> -	smc	#0
> -	ldp	x2, x3, [sp, #(8 * 0)]
> -	ldp	x0, x1, [sp, #(8 * 2)]
> -	add	sp, sp, #(8 * 4)
> -1:	.org __smccc_workaround_1_smc + __SMCCC_WORKAROUND_1_SMC_SZ
> -	.org 1b
> -SYM_CODE_END(__smccc_workaround_1_smc)
>  #endif
> diff --git a/arch/arm64/kvm/hyp/smccc_wa.S 
> b/arch/arm64/kvm/hyp/smccc_wa.S
> new file mode 100644
> index 000000000000..aa25b5428e77
> --- /dev/null
> +++ b/arch/arm64/kvm/hyp/smccc_wa.S
> @@ -0,0 +1,30 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2015-2018 - ARM Ltd
> + * Author: Marc Zyngier <marc.zyngier@....com>
> + */
> +
> +#include <linux/arm-smccc.h>
> +
> +#include <asm/kvm_asm.h>
> +#include <asm/kvm_mmu.h>
> +
> +	/*
> +	 * This is not executed directly and is instead copied into the 
> vectors
> +	 * by install_bp_hardening_cb().
> +	 */
> +	.data
> +	.pushsection	.rodata
> +	.global		__smccc_workaround_1_smc
> +__smccc_workaround_1_smc:

You probably want to replace this with SYM_DATA_START (and SYM_DATA_END 
at the end).

> +	esb
> +	sub	sp, sp, #(8 * 4)
> +	stp	x2, x3, [sp, #(8 * 0)]
> +	stp	x0, x1, [sp, #(8 * 2)]
> +	mov	w0, #ARM_SMCCC_ARCH_WORKAROUND_1
> +	smc	#0
> +	ldp	x2, x3, [sp, #(8 * 0)]
> +	ldp	x0, x1, [sp, #(8 * 2)]
> +	add	sp, sp, #(8 * 4)
> +1:	.org __smccc_workaround_1_smc + __SMCCC_WORKAROUND_1_SMC_SZ
> +	.org 1b

Otherwise, looks good.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...