KVM: x86: Introduce kvm_check_cpuid()

Use kvm_check_cpuid() to validate if userspace provides legal cpuid
settings and call it before KVM take any action to update CPUID or
update vcpu states based on given CPUID settings.
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Message-Id: <20200709043426.92712-2-xiaoyao.li@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/cpuid.c

@@ -54,7 +54,26 @@ static u32 xstate_required_size(u64 xstate_bv, bool compacted)
 
 #define F feature_bit
 
-int kvm_update_cpuid(struct kvm_vcpu *vcpu)
+static int kvm_check_cpuid(struct kvm_vcpu *vcpu)
+{
+	struct kvm_cpuid_entry2 *best;
+
+	/*
+	 * The existing code assumes virtual address is 48-bit or 57-bit in the
+	 * canonical address checks; exit if it is ever changed.
+	 */
+	best = kvm_find_cpuid_entry(vcpu, 0x80000008, 0);
+	if (best) {
+		int vaddr_bits = (best->eax & 0xff00) >> 8;
+
+		if (vaddr_bits != 48 && vaddr_bits != 57 && vaddr_bits != 0)
+			return -EINVAL;
+	}
+
+	return 0;
+}
+
+void kvm_update_cpuid(struct kvm_vcpu *vcpu)
 {
 	struct kvm_cpuid_entry2 *best;
 	struct kvm_lapic *apic = vcpu->arch.apic;
@@ -98,18 +117,6 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
 		     cpuid_entry_has(best, X86_FEATURE_XSAVEC)))
 		best->ebx = xstate_required_size(vcpu->arch.xcr0, true);
 
-	/*
-	 * The existing code assumes virtual address is 48-bit or 57-bit in the
-	 * canonical address checks; exit if it is ever changed.
-	 */
-	best = kvm_find_cpuid_entry(vcpu, 0x80000008, 0);
-	if (best) {
-		int vaddr_bits = (best->eax & 0xff00) >> 8;
-
-		if (vaddr_bits != 48 && vaddr_bits != 57 && vaddr_bits != 0)
-			return -EINVAL;
-	}
-
 	best = kvm_find_cpuid_entry(vcpu, KVM_CPUID_FEATURES, 0);
 	if (kvm_hlt_in_guest(vcpu->kvm) && best &&
 		(best->eax & (1 << KVM_FEATURE_PV_UNHALT)))
@@ -131,7 +138,6 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
 	kvm_pmu_refresh(vcpu);
 	vcpu->arch.cr4_guest_rsvd_bits =
 	    __cr4_reserved_bits(guest_cpuid_has, vcpu);
-	return 0;
 }
 
 static int is_efer_nx(void)
@@ -206,11 +212,16 @@ int kvm_vcpu_ioctl_set_cpuid(struct kvm_vcpu *vcpu,
 		vcpu->arch.cpuid_entries[i].padding[2] = 0;
 	}
 	vcpu->arch.cpuid_nent = cpuid->nent;
+	r = kvm_check_cpuid(vcpu);
+	if (r) {
+		vcpu->arch.cpuid_nent = 0;
+		kvfree(cpuid_entries);
+		goto out;
+	}
+
 	cpuid_fix_nx_cap(vcpu);
 	kvm_x86_ops.cpuid_update(vcpu);
-	r = kvm_update_cpuid(vcpu);
-	if (r)
-		vcpu->arch.cpuid_nent = 0;
+	kvm_update_cpuid(vcpu);
 
 	kvfree(cpuid_entries);
 out:
@@ -231,10 +242,14 @@ int kvm_vcpu_ioctl_set_cpuid2(struct kvm_vcpu *vcpu,
 			   cpuid->nent * sizeof(struct kvm_cpuid_entry2)))
 		goto out;
 	vcpu->arch.cpuid_nent = cpuid->nent;
-	kvm_x86_ops.cpuid_update(vcpu);
-	r = kvm_update_cpuid(vcpu);
-	if (r)
+	r = kvm_check_cpuid(vcpu);
+	if (r) {
 		vcpu->arch.cpuid_nent = 0;
+		goto out;
+	}
+
+	kvm_x86_ops.cpuid_update(vcpu);
+	kvm_update_cpuid(vcpu);
 out:
 	return r;
 }

arch/x86/kvm/cpuid.h

@@ -9,7 +9,7 @@
 extern u32 kvm_cpu_caps[NCAPINTS] __read_mostly;
 void kvm_set_cpu_caps(void);
 
-int kvm_update_cpuid(struct kvm_vcpu *vcpu);
+void kvm_update_cpuid(struct kvm_vcpu *vcpu);
 struct kvm_cpuid_entry2 *kvm_find_cpuid_entry(struct kvm_vcpu *vcpu,
 					      u32 function, u32 index);
 int kvm_dev_ioctl_get_cpuid(struct kvm_cpuid2 *cpuid,