KVM: x86: Warn if guest virtual address space is not 48-bits

The KVM emulator code assumes that the guest virtual address space (in 64-bit)
is 48-bits wide.  Fail the KVM_SET_CPUID and KVM_SET_CPUID2 ioctl if
userspace tries to create a guest that does not obey this restriction.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

2 files changed, 15 insertions, 8 deletions

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index f4bad87ef256..e28d798f7277 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -53,14 +53,14 @@ u64 kvm_supported_xcr0(void)
         return xcr0;
 }
 
-void kvm_update_cpuid(struct kvm_vcpu *vcpu)
+int kvm_update_cpuid(struct kvm_vcpu *vcpu)
 {
         struct kvm_cpuid_entry2 *best;
         struct kvm_lapic *apic = vcpu->arch.apic;
 
         best = kvm_find_cpuid_entry(vcpu, 1, 0);
         if (!best)
-                return;
+                return 0;
 
         /* Update OSXSAVE bit */
         if (cpu_has_xsave && best->function == 0x1) {
@@ -88,7 +88,17 @@ void kvm_update_cpuid(struct kvm_vcpu *vcpu)
                         xstate_required_size(vcpu->arch.xcr0);
         }
 
+        /*
+         * The existing code assumes virtual address is 48-bit in the canonical
+         * address checks; exit if it is ever changed.
+         */
+        best = kvm_find_cpuid_entry(vcpu, 0x80000008, 0);
+        if (best && ((best->eax & 0xff00) >> 8) != 48 &&
+                ((best->eax & 0xff00) >> 8) != 0)
+                return -EINVAL;
+
         kvm_pmu_cpuid_update(vcpu);
+        return 0;
 }
 
 static int is_efer_nx(void)
@@ -151,10 +161,9 @@ int kvm_vcpu_ioctl_set_cpuid(struct kvm_vcpu *vcpu,
         }
         vcpu->arch.cpuid_nent = cpuid->nent;
         cpuid_fix_nx_cap(vcpu);
-        r = 0;
         kvm_apic_set_version(vcpu);
         kvm_x86_ops->cpuid_update(vcpu);
-        kvm_update_cpuid(vcpu);
+        r = kvm_update_cpuid(vcpu);
 
 out_free:
         vfree(cpuid_entries);
@@ -178,9 +187,7 @@ int kvm_vcpu_ioctl_set_cpuid2(struct kvm_vcpu *vcpu,
         vcpu->arch.cpuid_nent = cpuid->nent;
         kvm_apic_set_version(vcpu);
         kvm_x86_ops->cpuid_update(vcpu);
-        kvm_update_cpuid(vcpu);
-        return 0;
-
+        r = kvm_update_cpuid(vcpu);
 out:
         return r;
 }
diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index 43b33e301e68..4452eedfaedd 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -3,7 +3,7 @@
 
 #include "x86.h"
 
-void kvm_update_cpuid(struct kvm_vcpu *vcpu);
+int 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,