[PATCH v4 1/5] KVM: x86: Introduce kvm_check_cpuid()

[Xiaoyao Li]

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...@intel.com>
---
 arch/x86/kvm/cpuid.c | 55 ++++++++++++++++++++++++++++----------------
 arch/x86/kvm/cpuid.h |  2 +-
 2 files changed, 36 insertions(+), 21 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index eebd66f86abe..1a053022a961 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/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;
 }
diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index 05434cd9342f..f136de1debad 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/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,
-- 
2.18.4