Re: [PATCH v3 02/15] arm64: kvm: Move __smccc_workaround_1_smc to .rodata

Marc Zyngier
2020-06-18T13:57:50Z

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@google.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@arm.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...