KVM: x86: Add a helper to retrieve userspace address from kvm_device_attr

Add a helper to handle converting the u64 userspace address embedded in
struct kvm_device_attr into a userspace pointer, it's all too easy to
forget the intermediate "unsigned long" cast as well as the truncation
check.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5481d22..76a5dcf 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4332,7 +4332,15 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
                break;
        }
        return r;
+}
+
+static inline void __user *kvm_get_attr_addr(struct kvm_device_attr *attr)
+{
+       void __user *uaddr = (void __user*)(unsigned long)attr->addr;
 
+       if ((u64)(unsigned long)uaddr != attr->addr)
+               return ERR_PTR(-EFAULT);
+       return uaddr;
 }
 
 long kvm_arch_dev_ioctl(struct file *filp,
@@ -5025,11 +5033,11 @@ static int kvm_arch_tsc_has_attr(struct kvm_vcpu *vcpu,
 static int kvm_arch_tsc_get_attr(struct kvm_vcpu *vcpu,
                                 struct kvm_device_attr *attr)
 {
-       u64 __user *uaddr = (u64 __user *)(unsigned long)attr->addr;
+       u64 __user *uaddr = kvm_get_attr_addr(attr);
        int r;
 
-       if ((u64)(unsigned long)uaddr != attr->addr)
-               return -EFAULT;
+       if (IS_ERR(uaddr))
+               return PTR_ERR(uaddr);
 
        switch (attr->attr) {
        case KVM_VCPU_TSC_OFFSET:
@@ -5048,12 +5056,12 @@ static int kvm_arch_tsc_get_attr(struct kvm_vcpu *vcpu,
 static int kvm_arch_tsc_set_attr(struct kvm_vcpu *vcpu,
                                 struct kvm_device_attr *attr)
 {
-       u64 __user *uaddr = (u64 __user *)(unsigned long)attr->addr;
+       u64 __user *uaddr = kvm_get_attr_addr(attr);
        struct kvm *kvm = vcpu->kvm;
        int r;
 
-       if ((u64)(unsigned long)uaddr != attr->addr)
-               return -EFAULT;
+       if (IS_ERR(uaddr))
+               return PTR_ERR(uaddr);
 
        switch (attr->attr) {
        case KVM_VCPU_TSC_OFFSET: {