Re: [PATCH 5.4] KVM: x86: Fix pkru save/restore when guest CR4.PKE=0, move it to x86.c

[Paolo Bonzini]

On 22/05/20 18:32, Babu Moger wrote:
> [Backported upstream commit 37486135d3a7b03acc7755b63627a130437f066a]
> 
> Though rdpkru and wrpkru are contingent upon CR4.PKE, the PKRU
> resource isn't. It can be read with XSAVE and written with XRSTOR.
> So, if we don't set the guest PKRU value here(kvm_load_guest_xsave_state),
> the guest can read the host value.
> 
> In case of kvm_load_host_xsave_state, guest with CR4.PKE clear could
> potentially use XRSTOR to change the host PKRU value.
> 
> While at it, move pkru state save/restore to common code and the
> host_pkru field to kvm_vcpu_arch.  This will let SVM support protection keys.
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: Jim Mattson <jmattson@xxxxxxxxxx>
> Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
>  arch/x86/include/asm/kvm_host.h |    1 +
>  arch/x86/kvm/vmx/vmx.c          |   18 ------------------
>  arch/x86/kvm/x86.c              |   17 +++++++++++++++++
>  3 files changed, 18 insertions(+), 18 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 4fc61483919a..e204c43ed4b0 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -550,6 +550,7 @@ struct kvm_vcpu_arch {
>  	unsigned long cr4;
>  	unsigned long cr4_guest_owned_bits;
>  	unsigned long cr8;
> +	u32 host_pkru;
>  	u32 pkru;
>  	u32 hflags;
>  	u64 efer;
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 04a8212704c1..728758880cb6 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1384,7 +1384,6 @@ void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>  
>  	vmx_vcpu_pi_load(vcpu, cpu);
>  
> -	vmx->host_pkru = read_pkru();
>  	vmx->host_debugctlmsr = get_debugctlmsr();
>  }
>  
> @@ -6541,11 +6540,6 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
>  
>  	kvm_load_guest_xcr0(vcpu);
>  
> -	if (static_cpu_has(X86_FEATURE_PKU) &&
> -	    kvm_read_cr4_bits(vcpu, X86_CR4_PKE) &&
> -	    vcpu->arch.pkru != vmx->host_pkru)
> -		__write_pkru(vcpu->arch.pkru);
> -
>  	pt_guest_enter(vmx);
>  
>  	atomic_switch_perf_msrs(vmx);
> @@ -6634,18 +6628,6 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
>  
>  	pt_guest_exit(vmx);
>  
> -	/*
> -	 * eager fpu is enabled if PKEY is supported and CR4 is switched
> -	 * back on host, so it is safe to read guest PKRU from current
> -	 * XSAVE.
> -	 */
> -	if (static_cpu_has(X86_FEATURE_PKU) &&
> -	    kvm_read_cr4_bits(vcpu, X86_CR4_PKE)) {
> -		vcpu->arch.pkru = rdpkru();
> -		if (vcpu->arch.pkru != vmx->host_pkru)
> -			__write_pkru(vmx->host_pkru);
> -	}
> -
>  	kvm_put_guest_xcr0(vcpu);
>  
>  	vmx->nested.nested_run_pending = 0;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 5d530521f11d..502a23313e7b 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -821,11 +821,25 @@ void kvm_load_guest_xcr0(struct kvm_vcpu *vcpu)
>  			xsetbv(XCR_XFEATURE_ENABLED_MASK, vcpu->arch.xcr0);
>  		vcpu->guest_xcr0_loaded = 1;
>  	}
> +
> +	if (static_cpu_has(X86_FEATURE_PKU) &&
> +	    (kvm_read_cr4_bits(vcpu, X86_CR4_PKE) ||
> +	     (vcpu->arch.xcr0 & XFEATURE_MASK_PKRU)) &&
> +	    vcpu->arch.pkru != vcpu->arch.host_pkru)
> +		__write_pkru(vcpu->arch.pkru);
>  }
>  EXPORT_SYMBOL_GPL(kvm_load_guest_xcr0);
>  
>  void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu)
>  {
> +	if (static_cpu_has(X86_FEATURE_PKU) &&
> +	    (kvm_read_cr4_bits(vcpu, X86_CR4_PKE) ||
> +	     (vcpu->arch.xcr0 & XFEATURE_MASK_PKRU))) {
> +		vcpu->arch.pkru = rdpkru();
> +		if (vcpu->arch.pkru != vcpu->arch.host_pkru)
> +			__write_pkru(vcpu->arch.host_pkru);
> +	}
> +
>  	if (vcpu->guest_xcr0_loaded) {
>  		if (vcpu->arch.xcr0 != host_xcr0)
>  			xsetbv(XCR_XFEATURE_ENABLED_MASK, host_xcr0);
> @@ -3437,6 +3451,9 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>  
>  	kvm_x86_ops->vcpu_load(vcpu, cpu);
>  
> +	/* Save host pkru register if supported */
> +	vcpu->arch.host_pkru = read_pkru();
> +
>  	fpregs_assert_state_consistent();
>  	if (test_thread_flag(TIF_NEED_FPU_LOAD))
>  		switch_fpu_return();
> 

Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>