KVM: x86: fix information leak to userland

commit 97e69aa6 upstream.

Structures kvm_vcpu_events, kvm_debugregs, kvm_pit_state2 and
kvm_clock_data are copied to userland with some padding and reserved
fields unitialized.  It leads to leaking of contents of kernel stack
memory.  We have to initialize them to zero.

In patch v1 Jan Kiszka suggested to fill reserved fields with zeros
instead of memset'ting the whole struct.  It makes sense as these
fields are explicitly marked as padding.  No more fields need zeroing.
Signed-off-by: Vasiliy Kulikov <segooon@gmail.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

arch/x86/kvm/x86.c

@@ -2102,6 +2102,7 @@ static int kvm_vm_ioctl_get_pit2(struct kvm *kvm, struct kvm_pit_state2 *ps)
 		sizeof(ps->channels));
 	ps->flags = kvm->arch.vpit->pit_state.flags;
 	mutex_unlock(&kvm->arch.vpit->pit_state.lock);
+	memset(&ps->reserved, 0, sizeof(ps->reserved));
 	return r;
 }
 
@@ -2439,6 +2440,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
 		now_ns = timespec_to_ns(&now);
 		user_ns.clock = kvm->arch.kvmclock_offset + now_ns;
 		user_ns.flags = 0;
+		memset(&user_ns.pad, 0, sizeof(user_ns.pad));
 
 		r = -EFAULT;
 		if (copy_to_user(argp, &user_ns, sizeof(user_ns)))