Re: KVM vulnerability report about cpuid instruction

[Wanpeng Li <kernellwp@xxxxxxxxx>]

2017-06-07 15:09 GMT+08:00 Moguofang (Dennis mo) <moguofang@xxxxxxxxxx>:
> Hello!
>         A new vulnerability discover by me.

Could you test something like this?

--------------------------->8-------------------------------------------------------------

Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index a181ae7..b927a42 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -779,19 +779,20 @@ int kvm_dev_ioctl_get_cpuid(struct kvm_cpuid2 *cpuid,

 static int move_to_next_stateful_cpuid_entry(struct kvm_vcpu *vcpu, int i)
 {
+    int j = i, nent = vcpu->arch.cpuid_nent;
     struct kvm_cpuid_entry2 *e = &vcpu->arch.cpuid_entries[i];
-    int j, nent = vcpu->arch.cpuid_nent;
+    struct kvm_cpuid_entry2 *ej;

     e->flags &= ~KVM_CPUID_FLAG_STATE_READ_NEXT;
     /* when no next entry is found, the current entry[i] is reselected */
-    for (j = i + 1; ; j = (j + 1) % nent) {
-        struct kvm_cpuid_entry2 *ej = &vcpu->arch.cpuid_entries[j];
-        if (ej->function == e->function) {
-            ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;
-            return j;
-        }
-    }
-    return 0; /* silence gcc, even though control never reaches here */
+    do {
+        j = (j + 1) % nent;
+        ej = &vcpu->arch.cpuid_entries[j];
+    } while(ej->function != e->function);
+
+    ej->flags |= KVM_CPUID_FLAG_STATE_READ_NEXT;
+
+    return j;
 }

 /* find an entry with matching function, matching index (if needed), and that