Re: [PATCH v4 1/2] KVM: arm/arm64: Add save/restore support for firmware workaround state

[Auger Eric <eric.auger@redhat.com>]

Hi Andre,

On 3/21/19 6:35 PM, Andre Przywara wrote:
> On Thu, 21 Mar 2019 13:54:07 +0100
> Auger Eric <eric.auger@redhat.com> wrote:
> 
> Hi Eric,
> 
> many thanks for looking at this!
> I was about to prepare a new revision.
> 
>> Hi Andre,
>>
>> On 3/1/19 12:43 AM, Andre Przywara wrote:
>>> KVM implements the firmware interface for mitigating cache speculation
>>> vulnerabilities. Guests may use this interface to ensure mitigation is
>>> active.
>>> If we want to migrate such a guest to a host with a different support
>>> level for those workarounds, migration might need to fail, to ensure that
>>> critical guests don't loose their protection.
>>>
>>> Introduce a way for userland to save and restore the workarounds state.
>>> On restoring we do checks that make sure we don't downgrade our
>>> mitigation level.
>>>
>>> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
>>> ---
>>>  arch/arm/include/asm/kvm_emulate.h   |  10 +++
>>>  arch/arm/include/uapi/asm/kvm.h      |  10 +++
>>>  arch/arm64/include/asm/kvm_emulate.h |  14 +++
>>>  arch/arm64/include/uapi/asm/kvm.h    |   9 ++
>>>  virt/kvm/arm/psci.c                  | 128 +++++++++++++++++++++++----
>>>  5 files changed, 155 insertions(+), 16 deletions(-)
>>>
>>> diff --git a/arch/arm/include/asm/kvm_emulate.h b/arch/arm/include/asm/kvm_emulate.h
>>> index 8927cae7c966..663a02d7e6f4 100644
>>> --- a/arch/arm/include/asm/kvm_emulate.h
>>> +++ b/arch/arm/include/asm/kvm_emulate.h
>>> @@ -283,6 +283,16 @@ static inline unsigned long kvm_vcpu_get_mpidr_aff(struct kvm_vcpu *vcpu)
>>>  	return vcpu_cp15(vcpu, c0_MPIDR) & MPIDR_HWID_BITMASK;
>>>  }
>>>  
>>> +static inline bool kvm_arm_get_vcpu_workaround_2_flag(struct kvm_vcpu *vcpu)
>>> +{
>>> +	return false;
>>> +}
>>> +
>>> +static inline void kvm_arm_set_vcpu_workaround_2_flag(struct kvm_vcpu *vcpu,
>>> +						      bool flag)
>>> +{
>>> +}
>>> +
>>>  static inline void kvm_vcpu_set_be(struct kvm_vcpu *vcpu)
>>>  {
>>>  	*vcpu_cpsr(vcpu) |= PSR_E_BIT;
>>> diff --git a/arch/arm/include/uapi/asm/kvm.h b/arch/arm/include/uapi/asm/kvm.h
>>> index 4602464ebdfb..ba4d2afe65e3 100644
>>> --- a/arch/arm/include/uapi/asm/kvm.h
>>> +++ b/arch/arm/include/uapi/asm/kvm.h
>>> @@ -214,6 +214,16 @@ struct kvm_vcpu_events {
>>>  #define KVM_REG_ARM_FW_REG(r)		(KVM_REG_ARM | KVM_REG_SIZE_U64 | \
>>>  					 KVM_REG_ARM_FW | ((r) & 0xffff))
>>>  #define KVM_REG_ARM_PSCI_VERSION	KVM_REG_ARM_FW_REG(0)
>>> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1	KVM_REG_ARM_FW_REG(1)
>>> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_AVAIL	0
>>> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_AVAIL	1
>>> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_UNAFFECTED	2
>>> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2	KVM_REG_ARM_FW_REG(2)
>>> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL	0
>>> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_UNKNOWN	1  
>> Would be worth adding a comment saying that values are chosen so that
>> higher values mean better protection. Otherwise it looks strange
>> NOT_AVAIL/AVAIL/UNAFFECTED values are not the same for both workarounds.	
>>> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_AVAIL	2
>>> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_UNAFFECTED	3
>>> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED	(1U << 4)  
>>
>>>  
>>>  /* Device Control API: ARM VGIC */
>>>  #define KVM_DEV_ARM_VGIC_GRP_ADDR	0
>>> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
>>> index d3842791e1c4..c00c17c9adb6 100644
>>> --- a/arch/arm64/include/asm/kvm_emulate.h
>>> +++ b/arch/arm64/include/asm/kvm_emulate.h
>>> @@ -348,6 +348,20 @@ static inline unsigned long kvm_vcpu_get_mpidr_aff(struct kvm_vcpu *vcpu)
>>>  	return vcpu_read_sys_reg(vcpu, MPIDR_EL1) & MPIDR_HWID_BITMASK;
>>>  }
>>>  
>>> +static inline bool kvm_arm_get_vcpu_workaround_2_flag(struct kvm_vcpu *vcpu)
>>> +{
>>> +	return vcpu->arch.workaround_flags & VCPU_WORKAROUND_2_FLAG;
>>> +}
>>> +
>>> +static inline void kvm_arm_set_vcpu_workaround_2_flag(struct kvm_vcpu *vcpu,
>>> +						      bool flag)
>>> +{
>>> +	if (flag)
>>> +		vcpu->arch.workaround_flags |= VCPU_WORKAROUND_2_FLAG;
>>> +	else
>>> +		vcpu->arch.workaround_flags &= ~VCPU_WORKAROUND_2_FLAG;
>>> +}
>>> +
>>>  static inline void kvm_vcpu_set_be(struct kvm_vcpu *vcpu)
>>>  {
>>>  	if (vcpu_mode_is_32bit(vcpu)) {
>>> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
>>> index 97c3478ee6e7..367e96fe654e 100644
>>> --- a/arch/arm64/include/uapi/asm/kvm.h
>>> +++ b/arch/arm64/include/uapi/asm/kvm.h
>>> @@ -225,6 +225,15 @@ struct kvm_vcpu_events {
>>>  #define KVM_REG_ARM_FW_REG(r)		(KVM_REG_ARM64 | KVM_REG_SIZE_U64 | \
>>>  					 KVM_REG_ARM_FW | ((r) & 0xffff))
>>>  #define KVM_REG_ARM_PSCI_VERSION	KVM_REG_ARM_FW_REG(0)
>>> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1	KVM_REG_ARM_FW_REG(1)
>>> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_AVAIL	0
>>> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_AVAIL	1
>>> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2	KVM_REG_ARM_FW_REG(2)
>>> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL	0
>>> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_UNKNOWN	1
>>> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_AVAIL	2
>>> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_UNAFFECTED	3
>>> +#define KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED     (1U << 4)
>>>  
>>>  /* Device Control API: ARM VGIC */
>>>  #define KVM_DEV_ARM_VGIC_GRP_ADDR	0
>>> diff --git a/virt/kvm/arm/psci.c b/virt/kvm/arm/psci.c
>>> index 9b73d3ad918a..e65664c09b12 100644
>>> --- a/virt/kvm/arm/psci.c
>>> +++ b/virt/kvm/arm/psci.c
>>> @@ -445,42 +445,97 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
>>>  
>>>  int kvm_arm_get_fw_num_regs(struct kvm_vcpu *vcpu)
>>>  {
>>> -	return 1;		/* PSCI version */
>>> +	return 3;		/* PSCI version and two workaround registers */
>>>  }
>>>  
>>>  int kvm_arm_copy_fw_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices)
>>>  {
>>> -	if (put_user(KVM_REG_ARM_PSCI_VERSION, uindices))
>>> +	if (put_user(KVM_REG_ARM_PSCI_VERSION, uindices++))
>>> +		return -EFAULT;
>>> +
>>> +	if (put_user(KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1, uindices++))
>>> +		return -EFAULT;
>>> +
>>> +	if (put_user(KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2, uindices++))
>>>  		return -EFAULT;  
>> Wouldn't it make sense to have a const array somewhere listing the FW
>> regs and putting KVM_REG_ARM_FW_REG[i]? Also kvm_arm_get_fw_num_regs
>> could return the ARRAY_SIZE.
> 
> Yeah, makes sense. I was cowardly pushing this off to the one adding the next firmware register ;-)

;-)
> 
>> vcpu arg is never used actually (not related to this patch).
>>>  
>>>  	return 0;
>>>  }
>>>  
>>> +#define KVM_REG_FEATURE_LEVEL_WIDTH	4
>>> +#define KVM_REG_FEATURE_LEVEL_MASK	(BIT(KVM_REG_FEATURE_LEVEL_WIDTH) - 1)
>>> +
>>> +/*
>>> + * Convert the workaround level into an easy-to-compare number, where higher
>>> + * values mean better protection.
>>> + */
>>> +static int get_kernel_wa_level(u64 regid)
>>> +{
>>> +	switch (regid) {
>>> +	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1:
>>> +		if (kvm_arm_harden_branch_predictor())
>>> +			return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_AVAIL;
>>> +		else
>>> +			return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_AVAIL;
>>> +	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2:
>>> +		switch (kvm_arm_have_ssbd()) {
>>> +		case KVM_SSBD_FORCE_DISABLE:
>>> +			return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL;
>>> +		case KVM_SSBD_KERNEL:
>>> +			return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_AVAIL;
>>> +		case KVM_SSBD_FORCE_ENABLE:
>>> +		case KVM_SSBD_MITIGATED:
>>> +			return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_UNAFFECTED;
>>> +		case KVM_SSBD_UNKNOWN:
>>> +		default:
>>> +			return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_UNKNOWN;
>>> +		}
>>> +	}
>>> +
>>> +	return 0;  
>> I would rather return -EINVAL although the function is not called for
>> any invalid reg.
>>> +}
>>> +
>>>  int kvm_arm_get_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>>>  {
>>> -	if (reg->id == KVM_REG_ARM_PSCI_VERSION) {
>>> -		void __user *uaddr = (void __user *)(long)reg->addr;
>>> -		u64 val;
>>> +	void __user *uaddr = (void __user *)(long)reg->addr;
>>> +	u64 val;
>>>  
>>> +	switch (reg->id) {
>>> +	case KVM_REG_ARM_PSCI_VERSION:
>>>  		val = kvm_psci_version(vcpu, vcpu->kvm);
>>> -		if (copy_to_user(uaddr, &val, KVM_REG_SIZE(reg->id)))
>>> -			return -EFAULT;
>>> -
>>> -		return 0;
>>> +		break;
>>> +	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1:
>>> +		val = get_kernel_wa_level(reg->id) & KVM_REG_FEATURE_LEVEL_MASK;  
>> Can get_kernel_wa_level return something outside of
>> KVM_REG_FEATURE_LEVEL_MASK?
>>> +		break;
>>> +	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2:
>>> +		val = get_kernel_wa_level(reg->id) & KVM_REG_FEATURE_LEVEL_MASK;  
>> same here
>>> +		if (kvm_arm_have_ssbd() == KVM_SSBD_KERNEL &&> +		    kvm_arm_get_vcpu_workaround_2_flag(vcpu))  
>> nit: if (val == KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_AVAIL &&
>> kvm_arm_get_vcpu_workaround_2_flag(vcpu)).
> 
> Yeah, might be better, since we operate in the KVM_REG_ARM_ namespace here.
> 
>>> +			val |= KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED;
>>> +		break;
>>> +	default:
>>> +		return -ENOENT;
>>>  	}
>>>  
>>> -	return -EINVAL;
>>> +	if (copy_to_user(uaddr, &val, KVM_REG_SIZE(reg->id)))
>>> +		return -EFAULT;
>>> +
>>> +	return 0;
>>>  }
>>>  
>>>  int kvm_arm_set_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>>>  {
>>> -	if (reg->id == KVM_REG_ARM_PSCI_VERSION) {
>>> -		void __user *uaddr = (void __user *)(long)reg->addr;
>>> -		bool wants_02;
>>> -		u64 val;
>>> +	void __user *uaddr = (void __user *)(long)reg->addr;
>>> +	u64 val;
>>> +	int wa_level;
>>> +
>>> +	if (copy_from_user(&val, uaddr, KVM_REG_SIZE(reg->id)))
>>> +		return -EFAULT;
>>>  
>>> -		if (copy_from_user(&val, uaddr, KVM_REG_SIZE(reg->id)))
>>> -			return -EFAULT;
>>> +	switch (reg->id) {
>>> +	case KVM_REG_ARM_PSCI_VERSION:
>>> +	{
>>> +		bool wants_02;
>>>  
>>>  		wants_02 = test_bit(KVM_ARM_VCPU_PSCI_0_2, vcpu->arch.features);
>>>  
>>> @@ -497,6 +552,47 @@ int kvm_arm_set_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>>>  			vcpu->kvm->arch.psci_version = val;
>>>  			return 0;
>>>  		}
>>> +		break;
>>> +	}
>>> +
>>> +	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1:
>>> +		if (val & ~KVM_REG_FEATURE_LEVEL_MASK)
>>> +			return -EINVAL;
>>> +
>>> +		wa_level = val & KVM_REG_FEATURE_LEVEL_MASK;  
>> not needed
> 
> Yeah, I kept it in for symmetry reasons. I was also afraid that someone
> changes the check above in the future.
> 
>>> +
>>> +		/* For now we only accept the very same workaround level. */
>>> +		if (get_kernel_wa_level(reg->id) != wa_level)
>>> +			return -EINVAL;
>>> +
>>> +		return 0;
>>> +
>>> +	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2:
>>> +		if (val & ~(KVM_REG_FEATURE_LEVEL_MASK |
>>> +			    KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED))> +			return -EINVAL;
>>> +
>>> +		wa_level = val & KVM_REG_FEATURE_LEVEL_MASK;
>>> +
>>> +		if (get_kernel_wa_level(reg->id) < wa_level)
>>> +			return -EINVAL;
>>> +  
>> worth a comment?
> 
> True.
> 
>>> +		if (kvm_arm_have_ssbd() != KVM_SSBD_KERNEL)
>>> +			return 0;
>>> +
>>> +		switch (wa_level) {
>>> +		case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_AVAIL:
>>> +			kvm_arm_set_vcpu_workaround_2_flag(vcpu,
>>> +			    val & KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_ENABLED);
>>> +			break;
>>> +		case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_UNAFFECTED:
>>> +			kvm_arm_set_vcpu_workaround_2_flag(vcpu, true);  
>> Looks strange to me we enable the flag when unaffected.
> 
> UNAFFECTED is the *requested* level here, so the original kernel had it.
> It means "always active or not needed". We get here if the local kernel
> has a *switchable* workaround, so we have to make sure it's enabled, to
> match the original workaround level.
> Will add a comment before the switch.

Yes that's clear now. I had hard time with the terminology to be honest.

Thanks

Eric
> 
> Cheers,
> Andre.
> 
> 
>>
>>> +			break;
>>> +		}
>>> +
>>> +		return 0;
>>> +	default:
>>> +		return -ENOENT;
>>>  	}
>>>  
>>>  	return -EINVAL;
>>>   
>>
>> Thanks
>>
>> Eric
> 
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