Subject: Re: [PATCH v2 5/5] KVM: arm64: Disable privileged hypercalls after pKVM finalisation

From: Marc Zyngier <[email-masked]>
Date: Thu, 07 Oct 2021 13:56:47 +0100

On Tue, 05 Oct 2021 12:37:21 +0100,
Will Deacon <[email-masked]> 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 <[email-masked]>
> Cc: Quentin Perret <[email-masked]>
> Signed-off-by: Will Deacon <[email-masked]>
> ---
>  arch/arm64/include/asm/kvm_asm.h   | 43 ++++++++++++++++--------------
>  arch/arm64/kvm/hyp/nvhe/hyp-main.c | 37 +++++++++++++++++--------
>  2 files changed, 49 insertions(+), 31 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> index e86045ac43ba..68630fd382c5 100644
> --- a/arch/arm64/include/asm/kvm_asm.h
> +++ b/arch/arm64/include/asm/kvm_asm.h
> @@ -43,27 +43,30 @@
>  
>  #define KVM_HOST_SMCCC_FUNC(name) KVM_HOST_SMCCC_ID(__KVM_HOST_SMCCC_FUNC_##name)
>  
> +/* Hypercalls available only prior to pKVM finalisation */
>  #define __KVM_HOST_SMCCC_FUNC___kvm_hyp_init			0
> -#define __KVM_HOST_SMCCC_FUNC___kvm_vcpu_run			1
> -#define __KVM_HOST_SMCCC_FUNC___kvm_flush_vm_context		2
> -#define __KVM_HOST_SMCCC_FUNC___kvm_tlb_flush_vmid_ipa		3
> -#define __KVM_HOST_SMCCC_FUNC___kvm_tlb_flush_vmid		4
> -#define __KVM_HOST_SMCCC_FUNC___kvm_flush_cpu_context		5
> -#define __KVM_HOST_SMCCC_FUNC___kvm_timer_set_cntvoff		6
> -#define __KVM_HOST_SMCCC_FUNC___kvm_enable_ssbs			7
> -#define __KVM_HOST_SMCCC_FUNC___vgic_v3_get_gic_config		8
> -#define __KVM_HOST_SMCCC_FUNC___vgic_v3_read_vmcr		9
> -#define __KVM_HOST_SMCCC_FUNC___vgic_v3_write_vmcr		10
> -#define __KVM_HOST_SMCCC_FUNC___vgic_v3_init_lrs		11
> -#define __KVM_HOST_SMCCC_FUNC___kvm_get_mdcr_el2		12
> -#define __KVM_HOST_SMCCC_FUNC___vgic_v3_save_aprs		13
> -#define __KVM_HOST_SMCCC_FUNC___vgic_v3_restore_aprs		14
> -#define __KVM_HOST_SMCCC_FUNC___pkvm_init			15
> -#define __KVM_HOST_SMCCC_FUNC___pkvm_host_share_hyp		16
> -#define __KVM_HOST_SMCCC_FUNC___pkvm_create_private_mapping	17
> -#define __KVM_HOST_SMCCC_FUNC___pkvm_cpu_set_vector		18
> -#define __KVM_HOST_SMCCC_FUNC___pkvm_prot_finalize		19
> -#define __KVM_HOST_SMCCC_FUNC___kvm_adjust_pc			20
> +#define __KVM_HOST_SMCCC_FUNC___kvm_get_mdcr_el2		1
> +#define __KVM_HOST_SMCCC_FUNC___pkvm_init			2
> +#define __KVM_HOST_SMCCC_FUNC___pkvm_create_private_mapping	3
> +#define __KVM_HOST_SMCCC_FUNC___pkvm_cpu_set_vector		4
> +#define __KVM_HOST_SMCCC_FUNC___kvm_enable_ssbs			5
> +#define __KVM_HOST_SMCCC_FUNC___vgic_v3_init_lrs		6
> +#define __KVM_HOST_SMCCC_FUNC___vgic_v3_get_gic_config		7
> +#define __KVM_HOST_SMCCC_FUNC___pkvm_prot_finalize		8
> +
> +/* Hypercalls available after pKVM finalisation */
> +#define __KVM_HOST_SMCCC_FUNC___pkvm_host_share_hyp		9
> +#define __KVM_HOST_SMCCC_FUNC___kvm_adjust_pc			10
> +#define __KVM_HOST_SMCCC_FUNC___kvm_vcpu_run			11
> +#define __KVM_HOST_SMCCC_FUNC___kvm_flush_vm_context		12
> +#define __KVM_HOST_SMCCC_FUNC___kvm_tlb_flush_vmid_ipa		13
> +#define __KVM_HOST_SMCCC_FUNC___kvm_tlb_flush_vmid		14
> +#define __KVM_HOST_SMCCC_FUNC___kvm_flush_cpu_context		15
> +#define __KVM_HOST_SMCCC_FUNC___kvm_timer_set_cntvoff		16
> +#define __KVM_HOST_SMCCC_FUNC___vgic_v3_read_vmcr		17
> +#define __KVM_HOST_SMCCC_FUNC___vgic_v3_write_vmcr		18
> +#define __KVM_HOST_SMCCC_FUNC___vgic_v3_save_aprs		19
> +#define __KVM_HOST_SMCCC_FUNC___vgic_v3_restore_aprs		20

This is no helping with the above, but can we *please* try to get rid
of this #define insanity before moving things around? I came up with
the following, which seems to build.

Thoughts?

	M.

>From 8a50c98489220d2ebaf02d4ffdbef3cf0d6634ee Mon Sep 17 00:00:00 2001
From: Marc Zyngier <[email-masked]>
Date: Thu, 7 Oct 2021 13:18:29 +0100
Subject: [PATCH] KVM: arm64: Turn __KVM_HOST_SMCCC_FUNC_* into an enum
 (mostly)

__KVM_HOST_SMCCC_FUNC_* is a royal pain, as there is a fair amount
of churn around these #defines, and we avoid making it an enum
only for the sake of the early init, low level code that requires
__KVM_HOST_SMCCC_FUNC___kvm_hyp_init to be usable from assembly.

Let's be brave and turn everything but this symbol into an enum,
using a bit of arithmetic to avoid any overlap.

Signed-off-by: Marc Zyngier <[email-masked]>
---
 arch/arm64/include/asm/kvm_asm.h | 44 +++++++++++++++++---------------
 1 file changed, 24 insertions(+), 20 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index e86045ac43ba..43b5e213ae43 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -44,31 +44,35 @@
 #define KVM_HOST_SMCCC_FUNC(name) KVM_HOST_SMCCC_ID(__KVM_HOST_SMCCC_FUNC_##name)
 
 #define __KVM_HOST_SMCCC_FUNC___kvm_hyp_init			0
-#define __KVM_HOST_SMCCC_FUNC___kvm_vcpu_run			1
-#define __KVM_HOST_SMCCC_FUNC___kvm_flush_vm_context		2
-#define __KVM_HOST_SMCCC_FUNC___kvm_tlb_flush_vmid_ipa		3
-#define __KVM_HOST_SMCCC_FUNC___kvm_tlb_flush_vmid		4
-#define __KVM_HOST_SMCCC_FUNC___kvm_flush_cpu_context		5
-#define __KVM_HOST_SMCCC_FUNC___kvm_timer_set_cntvoff		6
-#define __KVM_HOST_SMCCC_FUNC___kvm_enable_ssbs			7
-#define __KVM_HOST_SMCCC_FUNC___vgic_v3_get_gic_config		8
-#define __KVM_HOST_SMCCC_FUNC___vgic_v3_read_vmcr		9
-#define __KVM_HOST_SMCCC_FUNC___vgic_v3_write_vmcr		10
-#define __KVM_HOST_SMCCC_FUNC___vgic_v3_init_lrs		11
-#define __KVM_HOST_SMCCC_FUNC___kvm_get_mdcr_el2		12
-#define __KVM_HOST_SMCCC_FUNC___vgic_v3_save_aprs		13
-#define __KVM_HOST_SMCCC_FUNC___vgic_v3_restore_aprs		14
-#define __KVM_HOST_SMCCC_FUNC___pkvm_init			15
-#define __KVM_HOST_SMCCC_FUNC___pkvm_host_share_hyp		16
-#define __KVM_HOST_SMCCC_FUNC___pkvm_create_private_mapping	17
-#define __KVM_HOST_SMCCC_FUNC___pkvm_cpu_set_vector		18
-#define __KVM_HOST_SMCCC_FUNC___pkvm_prot_finalize		19
-#define __KVM_HOST_SMCCC_FUNC___kvm_adjust_pc			20
 
 #ifndef __ASSEMBLY__
 
 #include <linux/mm.h>
 
+enum __kvm_host_smccc_func {
+	/* __KVM_HOST_SMCCC_FUNC___kvm_hyp_init */
+	__KVM_HOST_SMCCC_FUNC___kvm_vcpu_run = __KVM_HOST_SMCCC_FUNC___kvm_hyp_init + 1,
+	__KVM_HOST_SMCCC_FUNC___kvm_flush_vm_context,
+	__KVM_HOST_SMCCC_FUNC___kvm_tlb_flush_vmid_ipa,
+	__KVM_HOST_SMCCC_FUNC___kvm_tlb_flush_vmid,
+	__KVM_HOST_SMCCC_FUNC___kvm_flush_cpu_context,
+	__KVM_HOST_SMCCC_FUNC___kvm_timer_set_cntvoff,
+	__KVM_HOST_SMCCC_FUNC___kvm_enable_ssbs,
+	__KVM_HOST_SMCCC_FUNC___vgic_v3_get_gic_config,
+	__KVM_HOST_SMCCC_FUNC___vgic_v3_read_vmcr,
+	__KVM_HOST_SMCCC_FUNC___vgic_v3_write_vmcr,
+	__KVM_HOST_SMCCC_FUNC___vgic_v3_init_lrs,
+	__KVM_HOST_SMCCC_FUNC___kvm_get_mdcr_el2,
+	__KVM_HOST_SMCCC_FUNC___vgic_v3_save_aprs,
+	__KVM_HOST_SMCCC_FUNC___vgic_v3_restore_aprs,
+	__KVM_HOST_SMCCC_FUNC___pkvm_init,
+	__KVM_HOST_SMCCC_FUNC___pkvm_host_share_hyp,
+	__KVM_HOST_SMCCC_FUNC___pkvm_create_private_mapping,
+	__KVM_HOST_SMCCC_FUNC___pkvm_cpu_set_vector,
+	__KVM_HOST_SMCCC_FUNC___pkvm_prot_finalize,
+	__KVM_HOST_SMCCC_FUNC___kvm_adjust_pc,
+};
+
 #define DECLARE_KVM_VHE_SYM(sym)	extern char sym[]
 #define DECLARE_KVM_NVHE_SYM(sym)	extern char kvm_nvhe_sym(sym)[]
 
-- 
2.30.2

-- 
Without deviation from the norm, progress is not possible.

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