KVM: Prevent overflow in KVM_GET_SUPPORTED_CPUID

The number of entries is multiplied by the entry size, which can
overflow on 32-bit hosts.  Bound the entry count instead.
Reported-by: David Wagner <daw@cs.berkeley.edu>
Cc: stable@kernel.org
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/x86.c

@@ -1591,6 +1591,8 @@ static int kvm_dev_ioctl_get_supported_cpuid(struct kvm_cpuid2 *cpuid,
 
 	if (cpuid->nent < 1)
 		goto out;
+	if (cpuid->nent > KVM_MAX_CPUID_ENTRIES)
+		cpuid->nent = KVM_MAX_CPUID_ENTRIES;
 	r = -ENOMEM;
 	cpuid_entries = vmalloc(sizeof(struct kvm_cpuid_entry2) * cpuid->nent);
 	if (!cpuid_entries)