[PATCH v2 1/6] Revert "KVM: x86: Skip EFER vs. guest CPUID checks for host-initiated writes"

[Sean Christopherson]

Revert the misguided-in-hindsight decision to allow userspace to violate
architectural consistency when setting EFER as it has since been solidified
that userspace is required to configure guest CPUID prior to setting MSRs,
and skipping the CR0.PG vs. EFER.LME check in allows userspace to load an
end state of EFER.LMA=1 && EFER.LME=0, which is supposed to be impossible
and trips a variety of KVM_BUG_ON()s in the MMU.

This reverts commit 11988499e62b310f3bf6f6d0a807a06d3f9ccc96.

Fixes: 11988499e62b ("KVM: x86: Skip EFER vs. guest CPUID checks for host-initiated writes")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kvm/msrs.c | 30 +++++++++---------------------
 1 file changed, 9 insertions(+), 21 deletions(-)

diff --git a/arch/x86/kvm/msrs.c b/arch/x86/kvm/msrs.c
index e91650af44c2..2df42276fd82 100644
--- a/arch/x86/kvm/msrs.c
+++ b/arch/x86/kvm/msrs.c
@@ -580,8 +580,11 @@ static int do_get_feature_msr(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
 				 kvm_get_feature_msr);
 }
 
-static bool __kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer)
+bool kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer)
 {
+	if (efer & ~kvm_caps.supported_efer_bits)
+		return false;
+
 	if (efer & EFER_AUTOIBRS && !guest_cpu_cap_has(vcpu, X86_FEATURE_AUTOIBRS))
 		return false;
 
@@ -610,33 +613,18 @@ static bool __kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer)
 
 	return true;
 }
-
-bool kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer)
-{
-	if (efer & ~kvm_caps.supported_efer_bits)
-		return false;
-
-	return __kvm_valid_efer(vcpu, efer);
-}
 EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_valid_efer);
 
-static int set_efer(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
+static int set_efer(struct kvm_vcpu *vcpu, u64 efer)
 {
 	u64 old_efer = vcpu->arch.efer;
-	u64 efer = msr_info->data;
 	int r;
 
-	if (efer & ~kvm_caps.supported_efer_bits)
+	if (!kvm_valid_efer(vcpu, efer))
 		return 1;
 
-	if (!msr_info->host_initiated) {
-		if (!__kvm_valid_efer(vcpu, efer))
-			return 1;
-
-		if (is_paging(vcpu) &&
-		    (vcpu->arch.efer & EFER_LME) != (efer & EFER_LME))
-			return 1;
-	}
+	if (is_paging(vcpu) && (vcpu->arch.efer & EFER_LME) != (efer & EFER_LME))
+		return 1;
 
 	efer &= ~EFER_LMA;
 	efer |= vcpu->arch.efer & EFER_LMA;
@@ -1547,7 +1535,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		wrmsrq(MSR_IA32_FLUSH_CMD, L1D_FLUSH);
 		break;
 	case MSR_EFER:
-		return set_efer(vcpu, msr_info);
+		return set_efer(vcpu, msr_info->data);
 	case MSR_K7_HWCR: {
 		/*
 		 * Allow McStatusWrEn and TscFreqSel. (Linux guests from v3.2
-- 
2.56.0.307.g5fe7bd680c-goog