Re: [PATCH 5/5] KVM: arm64: Disable privileged hypercalls after pKVM finalisation

From: Will Deacon <will@kernel.org>
To: linux-arm-kernel@lists.infradead.org
Cc: Marc Zyngier <maz@kernel.org>,
	Quentin Perret <qperret@google.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH 5/5] KVM: arm64: Disable privileged hypercalls after pKVM finalisation
Date: Thu, 23 Sep 2021 13:58:34 +0100	[thread overview]
Message-ID: <20210923125834.GA15934@willie-the-truck> (raw)
In-Reply-To: <20210923112256.15767-6-will@kernel.org>

On Thu, Sep 23, 2021 at 12:22:56PM +0100, Will Deacon wrote:
> After pKVM has been 'finalised' using the __pkvm_prot_finalize hypercall,
> the calling CPU will have a Stage-2 translation enabled to prevent access
> to memory pages owned by EL2.
> 
> Although this forms a significant part of the process to deprivilege the
> host kernel, we also need to ensure that the hypercall interface is
> reduced so that the EL2 code cannot, for example, be re-initialised using
> a new set of vectors.
> 
> Re-order the hypercalls so that only a suffix remains available after
> finalisation of pKVM.
> 
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Quentin Perret <qperret@google.com>
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
>  arch/arm64/include/asm/kvm_asm.h   | 43 ++++++++++++++++--------------
>  arch/arm64/kvm/hyp/nvhe/hyp-main.c | 26 +++++++++++-------
>  2 files changed, 39 insertions(+), 30 deletions(-)

[...]

> diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> index 2da6aa8da868..4120e34288e1 100644
> --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
> @@ -165,36 +165,42 @@ typedef void (*hcall_t)(struct kvm_cpu_context *);
>  #define HANDLE_FUNC(x)	[__KVM_HOST_SMCCC_FUNC_##x] = (hcall_t)handle_##x
>  
>  static const hcall_t host_hcall[] = {
> -	HANDLE_FUNC(__kvm_vcpu_run),
> +	/* ___kvm_hyp_init */
> +	HANDLE_FUNC(__kvm_get_mdcr_el2),
> +	HANDLE_FUNC(__pkvm_init),
> +	HANDLE_FUNC(__pkvm_create_private_mapping),
> +	HANDLE_FUNC(__pkvm_cpu_set_vector),
> +	HANDLE_FUNC(__kvm_enable_ssbs),
> +	HANDLE_FUNC(__vgic_v3_init_lrs),
> +	HANDLE_FUNC(__pkvm_prot_finalize),
> +
> +	HANDLE_FUNC(__pkvm_host_share_hyp),
>  	HANDLE_FUNC(__kvm_adjust_pc),
> +	HANDLE_FUNC(__kvm_vcpu_run),
>  	HANDLE_FUNC(__kvm_flush_vm_context),
>  	HANDLE_FUNC(__kvm_tlb_flush_vmid_ipa),
>  	HANDLE_FUNC(__kvm_tlb_flush_vmid),
>  	HANDLE_FUNC(__kvm_flush_cpu_context),
>  	HANDLE_FUNC(__kvm_timer_set_cntvoff),
> -	HANDLE_FUNC(__kvm_enable_ssbs),
>  	HANDLE_FUNC(__vgic_v3_get_gic_config),
>  	HANDLE_FUNC(__vgic_v3_read_vmcr),
>  	HANDLE_FUNC(__vgic_v3_write_vmcr),
> -	HANDLE_FUNC(__vgic_v3_init_lrs),
> -	HANDLE_FUNC(__kvm_get_mdcr_el2),
>  	HANDLE_FUNC(__vgic_v3_save_aprs),
>  	HANDLE_FUNC(__vgic_v3_restore_aprs),
> -	HANDLE_FUNC(__pkvm_init),
> -	HANDLE_FUNC(__pkvm_cpu_set_vector),
> -	HANDLE_FUNC(__pkvm_host_share_hyp),
> -	HANDLE_FUNC(__pkvm_create_private_mapping),
> -	HANDLE_FUNC(__pkvm_prot_finalize),

Not that it makes any functional difference, but I was trying to keep this
in numerical order and evidently didn't manage it after renumbering
__vgic_v3_get_gic_config. Will fix for v2.

Will

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