[PATCH v8 19/21] KVM: nVMX: Add FRED-related VMCS field checks

Xin Li (Intel)
2025-10-14T01:11:13Z

As with real hardware, nested VMX validates various VMCS fields, including
control and guest/host state fields. This patch adds checks for FRED-related
VMCS fields to support nested FRED functionality.

Signed-off-by: Xin Li <xin3.li@intel.com>
Signed-off-by: Xin Li (Intel) <xin@zytor.com>
Tested-by: Shan Kang <shan.kang@intel.com>
Tested-by: Xuelian Guo <xuelian.guo@intel.com>
---

Change in v5:
* Add TB from Xuelian Guo.
---
arch/x86/kvm/vmx/nested.c | 117 +++++++++++++++++++++++++++++++++-----
1 file changed, 104 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index aba2800b4012..bffd10b6fe25 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3031,6 +3031,8 @@ static int nested_check_vm_entry_controls(struct kvm_vcpu *vcpu,
struct vmcs12 *vmcs12)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
+ bool fred_enabled = (vmcs12->vm_entry_controls & VM_ENTRY_IA32E_MODE) &&
+ (vmcs12->guest_cr4 & X86_CR4_FRED);

if (CC(!vmx_control_verify(vmcs12->vm_entry_controls,
vmx->nested.msrs.entry_ctls_low,
@@ -3048,22 +3050,11 @@ static int nested_check_vm_entry_controls(struct kvm_vcpu *vcpu,
u8 vector = intr_info & INTR_INFO_VECTOR_MASK;
u32 intr_type = intr_info & INTR_INFO_INTR_TYPE_MASK;
bool has_error_code = intr_info & INTR_INFO_DELIVER_CODE_MASK;
+ bool has_nested_exception = vmx->nested.msrs.basic & VMX_BASIC_NESTED_EXCEPTION;
bool urg = nested_cpu_has2(vmcs12,
SECONDARY_EXEC_UNRESTRICTED_GUEST);
bool prot_mode = !urg || vmcs12->guest_cr0 & X86_CR0_PE;

- /* VM-entry interruption-info field: interruption type */
- if (CC(intr_type == INTR_TYPE_RESERVED) ||
- CC(intr_type == INTR_TYPE_OTHER_EVENT &&
- !nested_cpu_supports_monitor_trap_flag(vcpu)))
- return -EINVAL;
-
- /* VM-entry interruption-info field: vector */
- if (CC(intr_type == INTR_TYPE_NMI_INTR && vector != NMI_VECTOR) ||
- CC(intr_type == INTR_TYPE_HARD_EXCEPTION && vector > 31) ||
- CC(intr_type == INTR_TYPE_OTHER_EVENT && vector != 0))
- return -EINVAL;
-
/*
* Cannot deliver error code in real mode or if the interrupt
* type is not hardware exception. For other cases, do the
@@ -3087,8 +3078,28 @@ static int nested_check_vm_entry_controls(struct kvm_vcpu *vcpu,
if (CC(intr_info & INTR_INFO_RESVD_BITS_MASK))
return -EINVAL;

- /* VM-entry instruction length */
+ /*
+ * When the CPU enumerates VMX nested-exception support, bit 13
+ * (set to indicate a nested exception) of the intr info field
+ * may have value 1. Otherwise bit 13 is reserved.
+ */
+ if (CC(!(has_nested_exception && intr_type == INTR_TYPE_HARD_EXCEPTION) &&
+ intr_info & INTR_INFO_NESTED_EXCEPTION_MASK))
+ return -EINVAL;
+
switch (intr_type) {
+ case INTR_TYPE_EXT_INTR:
+ break;
+ case INTR_TYPE_RESERVED:
+ return -EINVAL;
+ case INTR_TYPE_NMI_INTR:
+ if (CC(vector != NMI_VECTOR))
+ return -EINVAL;
+ break;
+ case INTR_TYPE_HARD_EXCEPTION:
+ if (CC(vector > 31))
+ return -EINVAL;
+ break;
case INTR_TYPE_SOFT_EXCEPTION:
case INTR_TYPE_SOFT_INTR:
case INTR_TYPE_PRIV_SW_EXCEPTION:
@@ -3096,6 +3107,24 @@ static int nested_check_vm_entry_controls(struct kvm_vcpu *vcpu,
CC(vmcs12->vm_entry_instruction_len == 0 &&
CC(!nested_cpu_has_zero_length_injection(vcpu))))
return -EINVAL;
+ break;
+ case INTR_TYPE_OTHER_EVENT:
+ switch (vector) {
+ case 0:
+ if (CC(!nested_cpu_supports_monitor_trap_flag(vcpu)))
+ return -EINVAL;
+ break;
+ case 1:
+ case 2:
+ if (CC(!fred_enabled))
+ return -EINVAL;
+ if (CC(vmcs12->vm_entry_instruction_len > X86_MAX_INSTRUCTION_LENGTH))
+ return -EINVAL;
+ break;
+ default:
+ return -EINVAL;
+ }
+ break;
}
}

@@ -3182,9 +3211,29 @@ static int nested_vmx_check_host_state(struct kvm_vcpu *vcpu,
if (ia32e) {
if (CC(!(vmcs12->host_cr4 & X86_CR4_PAE)))
return -EINVAL;
+ if (vmcs12->vm_exit_controls & VM_EXIT_ACTIVATE_SECONDARY_CONTROLS &&
+ vmcs12->secondary_vm_exit_controls & SECONDARY_VM_EXIT_LOAD_IA32_FRED) {
+ if (CC(vmcs12->host_ia32_fred_config &
+ (BIT_ULL(11) | GENMASK_ULL(5, 4) | BIT_ULL(2))) ||
+ CC(vmcs12->host_ia32_fred_rsp1 & GENMASK_ULL(5, 0)) ||
+ CC(vmcs12->host_ia32_fred_rsp2 & GENMASK_ULL(5, 0)) ||
+ CC(vmcs12->host_ia32_fred_rsp3 & GENMASK_ULL(5, 0)) ||
+ CC(vmcs12->host_ia32_fred_ssp1 & GENMASK_ULL(2, 0)) ||
+ CC(vmcs12->host_ia32_fred_ssp2 & GENMASK_ULL(2, 0)) ||
+ CC(vmcs12->host_ia32_fred_ssp3 & GENMASK_ULL(2, 0)) ||
+ CC(is_noncanonical_msr_address(vmcs12->host_ia32_fred_config & PAGE_MASK, vcpu)) ||
+ CC(is_noncanonical_msr_address(vmcs12->host_ia32_fred_rsp1, vcpu)) ||
+ CC(is_noncanonical_msr_address(vmcs12->host_ia32_fred_rsp2, vcpu)) ||
+ CC(is_noncanonical_msr_address(vmcs12->host_ia32_fred_rsp3, vcpu)) ||
+ CC(is_noncanonical_msr_address(vmcs12->host_ia32_fred_ssp1, vcpu)) ||
+ CC(is_noncanonical_msr_address(vmcs12->host_ia32_fred_ssp2, vcpu)) ||
+ CC(is_noncanonical_msr_address(vmcs12->host_ia32_fred_ssp3, vcpu)))
+ return -EINVAL;
+ }
} else {
if (CC(vmcs12->vm_entry_controls & VM_ENTRY_IA32E_MODE) ||
CC(vmcs12->host_cr4 & X86_CR4_PCIDE) ||
+ CC(vmcs12->host_cr4 & X86_CR4_FRED) ||
CC((vmcs12->host_rip) >> 32))
return -EINVAL;
}
@@ -3353,6 +3402,48 @@ static int nested_vmx_check_guest_state(struct kvm_vcpu *vcpu,
CC((vmcs12->guest_bndcfgs & MSR_IA32_BNDCFGS_RSVD))))
return -EINVAL;

+ if (ia32e) {
+ if (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_IA32_FRED) {
+ if (CC(vmcs12->guest_ia32_fred_config &
+ (BIT_ULL(11) | GENMASK_ULL(5, 4) | BIT_ULL(2))) ||
+ CC(vmcs12->guest_ia32_fred_rsp1 & GENMASK_ULL(5, 0)) ||
+ CC(vmcs12->guest_ia32_fred_rsp2 & GENMASK_ULL(5, 0)) ||
+ CC(vmcs12->guest_ia32_fred_rsp3 & GENMASK_ULL(5, 0)) ||
+ CC(vmcs12->guest_ia32_fred_ssp1 & GENMASK_ULL(2, 0)) ||
+ CC(vmcs12->guest_ia32_fred_ssp2 & GENMASK_ULL(2, 0)) ||
+ CC(vmcs12->guest_ia32_fred_ssp3 & GENMASK_ULL(2, 0)) ||
+ CC(is_noncanonical_msr_address(vmcs12->guest_ia32_fred_config & PAGE_MASK, vcpu)) ||
+ CC(is_noncanonical_msr_address(vmcs12->guest_ia32_fred_rsp1, vcpu)) ||
+ CC(is_noncanonical_msr_address(vmcs12->guest_ia32_fred_rsp2, vcpu)) ||
+ CC(is_noncanonical_msr_address(vmcs12->guest_ia32_fred_rsp3, vcpu)) ||
+ CC(is_noncanonical_msr_address(vmcs12->guest_ia32_fred_ssp1, vcpu)) ||
+ CC(is_noncanonical_msr_address(vmcs12->guest_ia32_fred_ssp2, vcpu)) ||
+ CC(is_noncanonical_msr_address(vmcs12->guest_ia32_fred_ssp3, vcpu)))
+ return -EINVAL;
+ }
+ if (vmcs12->guest_cr4 & X86_CR4_FRED) {
+ unsigned int ss_dpl = VMX_AR_DPL(vmcs12->guest_ss_ar_bytes);
+ switch (ss_dpl) {
+ case 0:
+ if (CC(!(vmcs12->guest_cs_ar_bytes & VMX_AR_L_MASK)))
+ return -EINVAL;
+ break;
+ case 1:
+ case 2:
+ return -EINVAL;
+ case 3:
+ if (CC(vmcs12->guest_rflags & X86_EFLAGS_IOPL))
+ return -EINVAL;
+ if (CC(vmcs12->guest_interruptibility_info & GUEST_INTR_STATE_STI))
+ return -EINVAL;
+ break;
+ }
+ }
+ } else {
+ if (CC(vmcs12->guest_cr4 & X86_CR4_FRED))
+ return -EINVAL;
+ }
+
if (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_CET_STATE) {
if (nested_vmx_check_cet_state_common(vcpu, vmcs12->guest_s_cet,
vmcs12->guest_ssp,
--
2.51.0