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Subject[PATCH v9 4/7] KVM: VMX: Load CET states on vmentry/vmexit
Date
"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@linux.intel.com>
Signed-off-by: Zhang Yi Z <yi.z.zhang@linux.intel.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
---
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);
+}
+
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)
+{
+ 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));
+
+ if ((cr0 & X86_CR0_WP) && cet_allowed)
+ return true;
+
+ return false;
+}
+
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);
+
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
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