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KVM: VMX: Allow userspace to set all supported FEATURE_CONTROL bits

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Allow userspace to set all supported bits in MSR IA32_FEATURE_CONTROL
irrespective of the guest CPUID model, e.g. via KVM_SET_MSRS.  KVM's ABI
is that userspace is allowed to set MSRs before CPUID, i.e. can set MSRs
to values that would fault according to the guest CPUID model.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220607232353.3375324-2-seanjc@google.com
This commit is contained in:
Sean Christopherson
2022-06-07 23:23:51 +00:00
parent 0b5e7a16a0
commit d2a00af206
1 changed files with 32 additions and 6 deletions
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38
arch/x86/kvm/vmx/vmx.c
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@@ -1836,12 +1836,38 @@ bool nested_vmx_allowed(struct kvm_vcpu *vcpu)
return nested && guest_cpuid_has(vcpu, X86_FEATURE_VMX);
}
static inline bool vmx_feature_control_msr_valid(struct kvm_vcpu *vcpu,
uint64_t val)
{
uint64_t valid_bits = to_vmx(vcpu)->msr_ia32_feature_control_valid_bits;
/*
* Userspace is allowed to set any supported IA32_FEATURE_CONTROL regardless of
* guest CPUID. Note, KVM allows userspace to set "VMX in SMX" to maintain
* backwards compatibility even though KVM doesn't support emulating SMX. And
* because userspace set "VMX in SMX", the guest must also be allowed to set it,
* e.g. if the MSR is left unlocked and the guest does a RMW operation.
*/
#define KVM_SUPPORTED_FEATURE_CONTROL (FEAT_CTL_LOCKED | \
FEAT_CTL_VMX_ENABLED_INSIDE_SMX | \
FEAT_CTL_VMX_ENABLED_OUTSIDE_SMX | \
FEAT_CTL_SGX_LC_ENABLED | \
FEAT_CTL_SGX_ENABLED | \
FEAT_CTL_LMCE_ENABLED)
return !(val & ~valid_bits);
static inline bool vmx_feature_control_msr_valid(struct vcpu_vmx *vmx,
struct msr_data *msr)
{
uint64_t valid_bits;
/*
* Ensure KVM_SUPPORTED_FEATURE_CONTROL is updated when new bits are
* exposed to the guest.
*/
WARN_ON_ONCE(vmx->msr_ia32_feature_control_valid_bits &
~KVM_SUPPORTED_FEATURE_CONTROL);
if (msr->host_initiated)
valid_bits = KVM_SUPPORTED_FEATURE_CONTROL;
else
valid_bits = vmx->msr_ia32_feature_control_valid_bits;
return !(msr->data & ~valid_bits);
}
static int vmx_get_msr_feature(struct kvm_msr_entry *msr)
@@ -2240,7 +2266,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
vcpu->arch.mcg_ext_ctl = data;
break;
case MSR_IA32_FEAT_CTL:
if (!vmx_feature_control_msr_valid(vcpu, data) ||
if (!vmx_feature_control_msr_valid(vmx, msr_info) ||
(to_vmx(vcpu)->msr_ia32_feature_control &
FEAT_CTL_LOCKED && !msr_info->host_initiated))
return 1;