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
>
