Re: [PATCH v9 4/7] KVM: VMX: Load CET states on vmentry/vmexit

[Sean Christopherson]

On Fri, Dec 27, 2019 at 10:11:30AM +0800, Yang Weijiang wrote:
> "Load {guest,host} CET state" bit controls whether guest/host
> CET states will be loaded at VM entry/exit. Before doing that,
> KVM needs to check if CET can be enabled both on host and guest.
> 
> Note:
> 1)The processor does not allow CR4.CET to be set if CR0.WP = 0,
>   similarly, it does not allow CR0.WP to be cleared while CR4.CET = 1.
>   In either case, KVM would inject #GP to guest.
> 
> 2)SHSTK and IBT features share one control MSR:
>   MSR_IA32_{U,S}_CET, which means it's difficult to hide
>   one feature from another in the case of SHSTK != IBT,
>   after discussed in community, it's agreed to allow Guest
>   control two features independently as it won't introduce
>   security hole.
> 
> Co-developed-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
> Signed-off-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
> Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
> ---
>  arch/x86/kvm/vmx/capabilities.h | 10 ++++++
>  arch/x86/kvm/vmx/vmx.c          | 56 +++++++++++++++++++++++++++++++--
>  arch/x86/kvm/x86.c              |  3 ++
>  3 files changed, 67 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/capabilities.h b/arch/x86/kvm/vmx/capabilities.h
> index 7aa69716d516..4a67d35a42a2 100644
> --- a/arch/x86/kvm/vmx/capabilities.h
> +++ b/arch/x86/kvm/vmx/capabilities.h
> @@ -106,6 +106,16 @@ static inline bool vmx_mpx_supported(void)
>  		(vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_BNDCFGS);
>  }
>  
> +static inline bool cpu_has_load_guest_cet_states_ctrl(void)
> +{
> +	return ((vmcs_config.vmentry_ctrl) & VM_ENTRY_LOAD_GUEST_CET_STATE);
> +}
> +
> +static inline bool cpu_has_load_host_cet_states_ctrl(void)
> +{
> +	return ((vmcs_config.vmexit_ctrl) & VM_EXIT_LOAD_HOST_CET_STATE);

No need for parantheses around vmcs_config.vmexit_ctrl.

> +}
> +
>  static inline bool cpu_has_vmx_tpr_shadow(void)
>  {
>  	return vmcs_config.cpu_based_exec_ctrl & CPU_BASED_TPR_SHADOW;
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 61fc846c7ef3..95063cc7da89 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -44,6 +44,7 @@
>  #include <asm/spec-ctrl.h>
>  #include <asm/virtext.h>
>  #include <asm/vmx.h>
> +#include <asm/cet.h>
>  
>  #include "capabilities.h"
>  #include "cpuid.h"
> @@ -2445,7 +2446,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>  	      VM_EXIT_LOAD_IA32_EFER |
>  	      VM_EXIT_CLEAR_BNDCFGS |
>  	      VM_EXIT_PT_CONCEAL_PIP |
> -	      VM_EXIT_CLEAR_IA32_RTIT_CTL;
> +	      VM_EXIT_CLEAR_IA32_RTIT_CTL |
> +	      VM_EXIT_LOAD_HOST_CET_STATE;
>  	if (adjust_vmx_controls(min, opt, MSR_IA32_VMX_EXIT_CTLS,
>  				&_vmexit_control) < 0)
>  		return -EIO;
> @@ -2469,7 +2471,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
>  	      VM_ENTRY_LOAD_IA32_EFER |
>  	      VM_ENTRY_LOAD_BNDCFGS |
>  	      VM_ENTRY_PT_CONCEAL_PIP |
> -	      VM_ENTRY_LOAD_IA32_RTIT_CTL;
> +	      VM_ENTRY_LOAD_IA32_RTIT_CTL |
> +	      VM_ENTRY_LOAD_GUEST_CET_STATE;
>  	if (adjust_vmx_controls(min, opt, MSR_IA32_VMX_ENTRY_CTLS,
>  				&_vmentry_control) < 0)
>  		return -EIO;
> @@ -3027,6 +3030,25 @@ void vmx_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
>  	vmcs_writel(GUEST_CR3, guest_cr3);
>  }
>  
> +bool is_cet_bit_allowed(struct kvm_vcpu *vcpu)

This should be static.  I'd also include cr4 in the name, e.g.

  static bool is_cr4_set_allowed(...)


> +{
> +	u64 kvm_xss = kvm_supported_xss();
> +	unsigned long cr0;
> +	bool cet_allowed;
> +
> +	cr0 = kvm_read_cr0(vcpu);
> +
> +	/* Right now, only user-mode CET is supported.*/
> +	cet_allowed = (kvm_xss & XFEATURE_MASK_CET_USER) &&
> +		      (guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) ||
> +		      guest_cpuid_has(vcpu, X86_FEATURE_IBT));

Probably makes sense to add a "is_cet_supported()" helper.  That'd reduce
the amount of copy+paste and would probably add clarity to most flows.

> +
> +	if ((cr0 & X86_CR0_WP) && cet_allowed)
> +		return true;
> +
> +	return false;

	return (cr0 & X86_CR0_WP) && cet_allowed;

Even better, especially if you add is_cet_supported(), to avoid VMREAD of
CR0 when CET isn't supported.

	return is_cet_supported() && (kvm_read_cr0(vcpu) & X86_CR0_WP);

At that point, you can probably even forgo the helper, e.g.

	if ((cr4 & X86_CR4_CET) &&
	    (!is_cet_supported() || !(kvm_read_cr0(vcpu) & X86_CR0_WP)))
		return 1;

> +}
> +
>  int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
>  {
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
> @@ -3067,6 +3089,9 @@ int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
>  			return 1;
>  	}
>  
> +	if ((cr4 & X86_CR4_CET) && !is_cet_bit_allowed(vcpu))
> +		return 1;
> +
>  	if (vmx->nested.vmxon && !nested_cr4_valid(vcpu, cr4))
>  		return 1;
>  
> @@ -3930,6 +3955,12 @@ void vmx_set_constant_host_state(struct vcpu_vmx *vmx)
>  
>  	if (cpu_has_load_ia32_efer())
>  		vmcs_write64(HOST_IA32_EFER, host_efer);
> +
> +	if (cpu_has_load_host_cet_states_ctrl()) {
> +		vmcs_writel(HOST_S_CET, 0);
> +		vmcs_writel(HOST_INTR_SSP_TABLE, 0);
> +		vmcs_writel(HOST_SSP, 0);
> +	}
>  }
>  
>  void set_cr4_guest_host_mask(struct vcpu_vmx *vmx)
> @@ -6499,7 +6530,9 @@ bool __vmx_vcpu_run(struct vcpu_vmx *vmx, unsigned long *regs, bool launched);
>  static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
>  {
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
> +	u64 kvm_xss = kvm_supported_xss();
>  	unsigned long cr3, cr4;
> +	bool cet_allowed;
>  
>  	/* Record the guest's net vcpu time for enforced NMI injections. */
>  	if (unlikely(!enable_vnmi &&
> @@ -6530,6 +6563,25 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
>  		vmx->loaded_vmcs->host_state.cr3 = cr3;
>  	}
>  
> +	/* Right now, only user-mode CET is supported.*/
> +	cet_allowed = (kvm_xss & XFEATURE_MASK_CET_USER) &&
> +		      (guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) ||
> +		      guest_cpuid_has(vcpu, X86_FEATURE_IBT));
> +
> +	if (cpu_has_load_guest_cet_states_ctrl() && cet_allowed)
> +		vmcs_set_bits(VM_ENTRY_CONTROLS,
> +			      VM_ENTRY_LOAD_GUEST_CET_STATE);
> +	else
> +		vmcs_clear_bits(VM_ENTRY_CONTROLS,
> +				VM_ENTRY_LOAD_GUEST_CET_STATE);
> +
> +	if (cpu_has_load_host_cet_states_ctrl() && cet_allowed)
> +		vmcs_set_bits(VM_EXIT_CONTROLS,
> +			      VM_EXIT_LOAD_HOST_CET_STATE);
> +	else
> +		vmcs_clear_bits(VM_EXIT_CONTROLS,
> +				VM_EXIT_LOAD_HOST_CET_STATE);

Why are you clearing VMCS bits in vmx_vcpu_run()?  Unless I'm missing
something, these can go in vmx_cpuid_update().

> +
>  	cr4 = cr4_read_shadow();
>  	if (unlikely(cr4 != vmx->loaded_vmcs->host_state.cr4)) {
>  		vmcs_writel(HOST_CR4, cr4);
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index a9b1140d0508..b27d97eaec24 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -788,6 +788,9 @@ int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
>  	if (!(cr0 & X86_CR0_PG) && kvm_read_cr4_bits(vcpu, X86_CR4_PCIDE))
>  		return 1;
>  
> +	if (!(cr0 & X86_CR0_WP) && kvm_read_cr4_bits(vcpu, X86_CR4_CET))
> +		return 1;
> +
>  	kvm_x86_ops->set_cr0(vcpu, cr0);
>  
>  	if ((cr0 ^ old_cr0) & X86_CR0_PG) {
> -- 
> 2.17.2
>